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US FluView - Weekly Surveillance Flu report 2022/2023 season - for trend analysis

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  • #16
    Weekly U.S. Influenza Surveillance Report

    Print
    Updated February 3, 2023

    Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

    Key Updates for Week 4, ending January 28, 2023

    Seasonal influenza activity continues to decline across the country.
    Viruses


    Clinical Lab2.1%

    (Trend )


    positive for influenza
    this week


    Public Health Lab
    The most frequently reported viruses this week were influenza A(H3N2).

    Virus Characterization
    Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
    Illness


    Outpatient Respiratory Illness2.6%

    (Trend )


    of visits to a health care provider this week were for respiratory illness
    (above baseline).


    Outpatient Respiratory Illness: Activity Map
    This week 5 jurisdictions experienced moderate activity, 3 jurisdictions experienced high activity, and 1 experienced very high activity.

    Long-term Care Facilities1.1%

    (Trend )


    of facilities reported
    ≥ 1 influenza-positive test
    among residents this week.


    FluSurv-NET58.6 per 100,000


    cumulative hospitalization rate

    HHS Protect Hospitalizations2,671

    (Trend )


    patients admitted to hospitals with influenza
    this week.


    NCHS Mortality11.1%

    (Trend )


    of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

    Pediatric Deaths6


    deaths were reported this week for a total of
    97 so far this season


    All data are preliminary and may change as more reports are received.

    Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

    A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

    Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

    Key Points
    • Seasonal influenza activity continues to decline across the country.
    • Seven of 10 HHS regions were below their outpatient respiratory illness baselines.
    • The number and weekly rate of flu hospital admissions decreased compared to week 3.
      • Hospitals reported 2,671 influenza hospitalizations to HHS Protect during week 4 compared to 4,028 reported during week 3.
      • The weekly rate of flu hospital admissions in the FluSurv-NET declined again during week 4. However, the season’s cumulative hospitalization rate was 1.1 times higher than the highest cumulative in-season hospitalization rate observed for week 3 during previous seasons going back to 2010-2011. This in-season rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons going back to 2010-2011.
    • Of influenza A viruses detected and subtyped during week 4, 62% were influenza A(H3N2) and 38% were influenza A(H1N1).
    • Six influenza-associated pediatric deaths that occurred during the 2022-23 season were reported this week, for a total of 97 pediatric flu deaths reported so far this season.
    • CDC estimates that, so far this season, there have been at least 25 million illnesses, 280,000 hospitalizations, and 17,000 deaths from flu.
    • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
    • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (99.9%) have been susceptible to the influenza antiviral oseltamivir.
    • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
    U.S. Virologic Surveillance


    The percentage of specimens testing positive for influenza in clinical laboratories declined ≥ 0.5 percentage points compared to the previous week in all regions except regions 3 and 6, which remained stable. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
    Clinical Laboratories


    The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

    No. of specimens tested 69,223 2,119,678
    No. of positive specimens (%) 1,483 (2.1%) 323,036 (15.2%)
    Positive specimens by type
    Influenza A 1,396 (94.1%) 320,603 (99.2%)
    Influenza B 87 (5.9%) 2,433 (0.8%)


    View Chart Data | View Full Screen
    Public Health Laboratories


    The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
    No. of specimens tested 5,495 155,842
    No. of positive specimens 166 25,576
    Positive specimens by type/subtype
    Influenza A 165 (99.4%) 25,454 (99.5%)
    (H1N1)pdm09 44 (37.6%) 5,103 (24.3%)
    H3N2 73 (62.4%) 15,858 (75.7%)
    H3N2v 0 1 (<0.1%)
    Subtyping not performed 48 4,492
    Influenza B 1 (0.6%) 122 (0.5%)
    Yamagata lineage 0 0
    Victoria lineage 0 85 (100%)
    Lineage not performed 1 37


    View Chart Data | View Full Screen

    Additional virologic surveillance information for current and past seasons:
    Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
    Influenza Virus Characterization


    CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

    CDC genetically characterized 1,693 influenza viruses collected since October 2, 2022.
    A/H1 591
    6B.1A 591 (100%) 5a.1 1 (0.2%)
    5a.2 590 (99.8%)
    A/H3 1,073
    3C.2a1b 1,073 (100%) 1a 0
    1b 0
    2a 0
    2a.1 0
    2a.2 1,073 (100%)
    3C.3a 0 3a 0
    B/Victoria 29
    V1A 29 (100%) V1A 0
    V1A.1 0
    V1A.3 4 (13.8%)
    V1A.3a 0
    V1A.3a.1 0
    V1A.3a.2 25 (86.2%)
    B/Yamagata 0
    Y3 0
    CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria, and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell- or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

    Influenza A Viruses
    • A (H1N1)pdm09: Seventy-nine A(H1N1)pdm09 viruses were antigenically characterized by HI, and 78 (98.7%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
    • A (H3N2): One hundred and fifty-eight A(H3N2) viruses were antigenically characterized by HINT, and 147 (93.0%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

    Influenza B Viruses
    • B/Victoria: Twelve influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
    • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

    Assessment of Virus Susceptibility to Antiviral Medications

    CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

    Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
    Neuraminidase
    Inhibitors
    Oseltamivir Viruses
    Tested
    1,691 591 1,071 29 0
    Reduced
    Inhibition
    1 (0.1%) 1 (0.2%) 0 (0%) 0 (0%) 0 (0%)
    Highly
    Reduced
    Inhibition
    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Peramivir Viruses
    Tested
    1,691 591 1,071 29 0
    Reduced
    Inhibition
    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Highly
    Reduced
    Inhibition
    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Zanamivir Viruses
    Tested
    1,691 591 1,071 29 0
    Reduced
    Inhibition
    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Highly
    Reduced
    Inhibition
    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
    Tested
    1,647 568 1,050 29 0
    Reduced
    Susceptibility
    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
    Outpatient Respiratory Illness Surveillance


    The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
    Outpatient Respiratory Illness Visits


    Nationwide during week 4, 2.6% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable compared to what was reported in week 3 and remains above the national baseline of 2.5%. Seven of the 10 HHS regions are below their respective baselines, and regions 2, 3, and 9 are above their respective baselines. The percent of patient visits for respiratory illness remained stable for seven regions during week 4 compared to week 3, declined in regions 1 and 2, and increased in region 6. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



    * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

    View Chart Data (current season only) | View Full Screen
    Outpatient Respiratory Illness Visits by Age Group


    More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

    The percentage of visits for respiratory illness reported in ILINet decreased in the 50-64 years and 65+ years age groups and remained stable (change of ≤ 0.1 percentage point) in the 0-4 years, 5-24 years, and 25-49 years age groups in week 4 compared to week 3.



    View Chart Data | View Full Screen
    Outpatient Respiratory Illness Activity Map


    Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
    Week 4
    (Week ending
    Jan. 28, 2023)
    Week 3
    (Week ending
    Jan. 21, 2022)
    Week 4
    (Week ending
    Jan. 28, 2023)
    Week 3
    (Week ending
    Jan. 21, 2022)
    Very High 1 0 3 3
    High 3 4 23 26
    Moderate 5 6 46 49
    Low 15 14 128 126
    Minimal 31 30 483 485
    Insufficient Data 0 1 246 240



    *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

    Additional information about medically attended visits for ILI for current and past seasons:
    Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
    Long-term Care Facility (LTCF) Surveillance


    LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 4, 164 (1.1%) of 14,384 reporting facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 3.


    View Chart Data | View Full Screen

    Additional information about long-term care facility surveillance:
    Surveillance Methods | Additional Data
    Hospitalization Surveillance

    FluSurv-NET


    The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 13 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

    A total of 17,149 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and January 28, 2023. The weekly hospitalization rate observed in week 4 was 0.3 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-18 season which peaked during week 1 (week ending January 6, 2018) and the 2014-15 season which peaked during week 52 (week ending December 27, 2014).

    The overall cumulative hospitalization rate was 58.6 per 100,000 population. This cumulative hospitalization rate is 1.1 times higher than the highest cumulative in-season hospitalization rate observed in week 4 during previous seasons going back to 2010-2011 (prior season rates ranged from 0.5 per 100,000 to 51.4 per 100,000). However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons (2015-16, 2013-14, 2011-12, 2010-11 seasons).

    When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (173.2). Among adults aged 65 and older, rates were highest among adults aged 85 and older (316.3). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (78), followed by adults aged 50-64 years (62.5). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (83.5), followed by non-Hispanic American Indian or Alaska Native persons (71.8), non-Hispanic White persons (49.0), Hispanic/Latino persons (44.3), and non-Hispanic Asian/Pacific Islander persons (24.6).

    Among 17,149 hospitalizations, 16,667 (97.2%) were associated with influenza A virus, 312 (1.8%) with influenza B virus, 24 (0.1%) with influenza A virus and influenza B virus co-infection, and 146 (0.9%) with influenza virus for which the type was not determined. Among 3,626 hospitalizations with influenza A subtype information, 2,769 (76.4%) were A(H3N2), and 857 (23.6%) were A(H1N1)pdm09. Based on preliminary data, of the 3,181 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.4% (95% CI: 2.8%-4.1%) also tested positive for SARS-CoV-2.

    Among 2,256 hospitalized adults with information on underlying medical conditions, 96.7% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 754 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 40.8% were pregnant. Among 764 hospitalized children with information on underlying medical conditions, 66.8% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity, and neurologic disease.



    View Full Screen



    View Full Screen

    Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
    Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
    HHS Protect Hospitalization Surveillance


    Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 4, 2,671 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 3.


    View Chart Data | View Full Screen

    Additional HHS Protect hospitalization surveillance information:
    Surveillance Methods | Additional Data
    Mortality Surveillance

    National Center for Health Statistics (NCHS) Mortality Surveillance


    Based on NCHS mortality surveillance data available on February 2, 2023, 11.1% of the deaths that occurred during the week ending January 28, 2023 (week 4), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage decreased (> 0.3 percentage point change) compared to week 3 and is above the epidemic threshold of 7.2% for this week. Among the 2,690 PIC deaths reported for this week, 1,246 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 129 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December and has been decreasing for the past six weeks. The data presented are preliminary and may change as more data are received and processed.

    View Chart Data | View Full Screen

    Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
    Surveillance Methods | FluView Interactive
    Influenza-Associated Pediatric Mortality


    Six influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 4. The deaths occurred during week 47 of 2022 (the week ending November 26, 2022) and during weeks 1, 2, and 3 of 2023 (the weeks ending January 7, 2023, January 14, 2023, and January 21, 2023, respectively). All six deaths were associated with influenza A viruses. Four of the influenza A viruses had subtyping performed; two were A(H1N1) viruses and two were A(H3) viruses.

    A total of 97 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

    View Full Screen

    Additional pediatric mortality surveillance information for current and past seasons:
    Surveillance Methods | FluView Interactive
    Trend Indicators


    Increasing:
    Decreasing:
    Stable:
    Indicators Status by System


    Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
    Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
    Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
    HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
    NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

    Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

    Comment


    • #17
      Weekly U.S. Influenza Surveillance Report

      Print
      Updated February 10, 2023

      Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

      Key Updates for Week 5, ending February 4, 2023

      Seasonal influenza activity is low nationally.
      Viruses


      Clinical Lab1.7%

      (Trend )


      positive for influenza
      this week


      Public Health Lab
      The most frequently reported viruses this week were influenza A(H3N2).

      Virus Characterization
      Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
      Illness


      Outpatient Respiratory Illness2.6%

      (Trend )


      of visits to a health care provider this week were for respiratory illness
      (above baseline).


      Outpatient Respiratory Illness: Activity Map
      This week 6 jurisdictions experienced moderate activity and 3 jurisdictions experienced high activity.

      Long-term Care Facilities0.9%

      (Trend )


      of facilities reported
      ≥ 1 influenza-positive test
      among residents this week.


      FluSurv-NET59.2 per 100,000


      cumulative hospitalization rate

      HHS Protect Hospitalizations2,137

      (Trend )


      patients admitted to hospitals with influenza
      this week.


      NCHS Mortality10.4%

      (Trend )


      of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

      Pediatric Deaths9


      deaths were reported this week for a total of
      106 so far this season


      All data are preliminary and may change as more reports are received.

      Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

      A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

      Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

      Key Points
      • Seasonal influenza activity is low nationally.
      • Seven of 10 HHS regions were below their outpatient respiratory illness baselines.
      • The number and weekly rate of flu hospital admissions decreased compared to week 4.
        • Hospitals reported 2,137 influenza hospitalizations to HHS Protect during week 5 compared to 2,678 reported during week 4.
        • The weekly rate of flu hospital admissions in the FluSurv-NET declined again during week 5.
      • Of influenza A viruses detected and subtyped during week 5, 54.2% were influenza A(H3N2) and 45.8% were influenza A(H1N1).
      • Nine influenza-associated pediatric deaths that occurred during the 2022-23 season were reported this week, for a total of 106 pediatric flu deaths reported so far this season.
      • CDC estimates that, so far this season, there have been at least 25 million illnesses, 280,000 hospitalizations, and 18,000 deaths from flu.
      • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
      • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (99.9%) have been susceptible to the influenza antiviral oseltamivir.
      • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
      • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
      U.S. Virologic Surveillance


      Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
      Clinical Laboratories


      The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

      No. of specimens tested 65,550 2,212,459
      No. of positive specimens (%) 1,107 (1.7%) 324,722 (14.7%)
      Positive specimens by type
      Influenza A 998 (90.2%) 322,122 (99.2%)
      Influenza B 109 (9.8%) 2,599 (0.8%)


      View Chart Data | View Full Screen
      Public Health Laboratories


      The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
      No. of specimens tested 5,463 164,523
      No. of positive specimens 115 26,069
      Positive specimens by type/subtype
      Influenza A 109 (94.8%) 25,933 (99.5%)
      (H1N1)pdm09 38 (45.8%) 5,266 (24.6%)
      H3N2 45 (54.2%) 16,109 (75.4%)
      H3N2v 0 1 (<0.1%)
      Subtyping not performed 26 4,557
      Influenza B 6 (5.2%) 136 (0.5%)
      Yamagata lineage 0 0
      Victoria lineage 4 (100%) 97 (100%)
      Lineage not performed 2 39


      View Chart Data | View Full Screen

      Additional virologic surveillance information for current and past seasons:
      Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
      Influenza Virus Characterization


      CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

      CDC genetically characterized 1,903 influenza viruses collected since October 2, 2022.
      A/H1 671
      6B.1A 671 (100%) 5a.1 3 (0.4%)
      5a.2 668 (99.6%)
      A/H3 1,202
      3C.2a1b 1,202 (100%) 1a 0
      1b 0
      2a 0
      2a.1 0
      2a.2 1,202 (100%)
      3C.3a 0 3a 0
      B/Victoria 30
      V1A 30 (100%) V1A 0
      V1A.1 0
      V1A.3 4 (13.3%)
      V1A.3a 0
      V1A.3a.1 0
      V1A.3a.2 26 (86.7%)
      B/Yamagata 0
      Y3 0
      CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria, and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell- or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

      Influenza A Viruses
      • A (H1N1)pdm09: Eighty-five A(H1N1)pdm09 viruses were antigenically characterized by HI, and 84 (98.8%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
      • A (H3N2): One hundred and seventy-four A(H3N2) viruses were antigenically characterized by HINT, and 163 (93.7%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

      Influenza B Viruses
      • B/Victoria: Twelve influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
      • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

      Assessment of Virus Susceptibility to Antiviral Medications

      CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

      Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
      Neuraminidase
      Inhibitors
      Oseltamivir Viruses
      Tested
      1,903 672 1,201 30 0
      Reduced
      Inhibition
      1 (0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
      Highly
      Reduced
      Inhibition
      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
      Peramivir Viruses
      Tested
      1,903 672 1,201 30 0
      Reduced
      Inhibition
      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
      Highly
      Reduced
      Inhibition
      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
      Zanamivir Viruses
      Tested
      1,903 672 1,201 30 0
      Reduced
      Inhibition
      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
      Highly
      Reduced
      Inhibition
      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
      PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
      Tested
      1,844 639 1,175 30 0
      Reduced
      Susceptibility
      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
      One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
      Outpatient Respiratory Illness Surveillance


      The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
      Outpatient Respiratory Illness Visits


      Nationwide during week 5, 2.6% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable (change of ≤ 0.1 percentage point) compared to what was reported in week 4 and remains above the national baseline of 2.5%. Seven of the 10 HHS regions are below their respective baselines, and regions 2, 3, and 9 are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



      * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

      View Chart Data (current season only) | View Full Screen
      Outpatient Respiratory Illness Visits by Age Group


      More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

      The percentage of visits for respiratory illness reported in ILINet increased in the 0-4 years and 5-24 years age groups, while the 25-49, 50-64, and 65+ years age groups remained stable (change of ≤ 0.1 percentage point) in week 5 compared to week 4.



      View Chart Data | View Full Screen
      Outpatient Respiratory Illness Activity Map


      Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
      Week 5
      (Week ending
      Feb. 4, 2023)
      Week 4
      (Week ending
      Jan. 28, 2023)
      Week 5
      (Week ending
      Feb. 4, 2023)
      Week 4
      (Week ending
      Jan. 28, 2023)
      Very High 0 1 1 4
      High 3 3 26 23
      Moderate 6 6 42 49
      Low 11 16 131 126
      Minimal 35 29 482 489
      Insufficient Data 0 0 247 238



      *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

      Additional information about medically attended visits for ILI for current and past seasons:
      Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
      Long-term Care Facility (LTCF) Surveillance


      LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 5, 132 (0.9%) of 14,344 reporting facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 4.


      View Chart Data | View Full Screen

      Additional information about long-term care facility surveillance:
      Surveillance Methods | Additional Data
      Hospitalization Surveillance

      FluSurv-NET


      The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 13 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

      A total of 17,330 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and February 4, 2023. The weekly hospitalization rate observed in week 5 was 0.3 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-18 season, which peaked during week 1 (week ending January 6, 2018), and the 2014-15 season, which peaked during week 52 (week ending December 27, 2014).

      The overall cumulative hospitalization rate was 59.2 per 100,000 population. This cumulative hospitalization rate is the second highest cumulative in-season hospitalization rate observed in week 5 during previous seasons going back to 2010-2011, following the 2017-18 season. However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons (2015-16, 2013-14, 2011-12, 2010-11 seasons).

      When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (175.2). Among adults aged 65 and older, rates were highest among adults aged 85 and older (320.6). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (78.6), followed by adults aged 50-64 years (63.4). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (84.2), followed by non-Hispanic American Indian or Alaska Native persons (72.8), non-Hispanic White persons (49.5), Hispanic/Latino persons (44.8), and non-Hispanic Asian/Pacific Islander persons (24.8).

      Among 17,330 hospitalizations,16,831 (97.1%) were associated with influenza A virus, 325 (1.9%) with influenza B virus, 24 (0.1%) with influenza A virus and influenza B virus co-infection, and 150 (0.9%) with influenza virus for which the type was not determined. Among 3,734 hospitalizations with influenza A subtype information, 2,828 (75.7%) were A(H3N2), and 906 (24.3%) were A(H1N1)pdm09. Based on preliminary data, of the 3,728 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.5% (95% CI: 3.0%-4.2%) also tested positive for SARS-CoV-2.

      Among 2,663 hospitalized adults with information on underlying medical conditions, 96.5% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 854 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 39.7% were pregnant. Among 881 hospitalized children with information on underlying medical conditions, 65.6% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity and neurologic disease.



      View Full Screen



      View Full Screen

      Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
      Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
      HHS Protect Hospitalization Surveillance


      Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 5, 2,137 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 4.


      View Chart Data | View Full Screen

      Additional HHS Protect hospitalization surveillance information:
      Surveillance Methods | Additional Data
      Mortality Surveillance

      National Center for Health Statistics (NCHS) Mortality Surveillance


      Based on NCHS mortality surveillance data available on February 9, 2023, 10.4% of the deaths that occurred during the week ending February 4, 2023 (week 5), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage decreased (> 0.3 percentage point change) compared to week 4 and is above the epidemic threshold of 7.2% for this week. Among the 2,501 PIC deaths reported for this week, 1,167 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 44 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December and has been decreasing for the past seven weeks. The data presented are preliminary and may change as more data are received and processed.

      View Chart Data | View Full Screen

      Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
      Surveillance Methods | FluView Interactive
      Influenza-Associated Pediatric Mortality


      Nine influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 5. The deaths occurred between week 45 of 2022 (the week ending November 12, 2022) and week 5 of 2023 (the week ending February 4, 2023). Eight of the deaths were associated with influenza A viruses and one death was associated with an influenza B virus with no lineage determined. Five of the influenza A viruses had subtyping performed; all five were A(H3) viruses.

      A total of 106 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

      View Full Screen

      Additional pediatric mortality surveillance information for current and past seasons:
      Surveillance Methods | FluView Interactive
      Trend Indicators


      Increasing:
      Decreasing:
      Stable:
      Indicators Status by System


      Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
      Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
      Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
      HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
      NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

      Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

      Comment


      • #18
        Weekly U.S. Influenza Surveillance Report

        Print
        Updated February 17, 2023

        Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

        Key Updates for Week 6, ending February 11, 2023

        Seasonal influenza activity is low nationally.
        Viruses


        Clinical Lab1.4%

        (Trend )


        positive for influenza
        this week


        Public Health Lab
        The most frequently reported viruses this week were influenza A(H1N1).

        Virus Characterization
        Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
        Illness


        Outpatient Respiratory Illness2.6%

        (Trend )


        of visits to a health care provider this week were for respiratory illness
        (above baseline).


        Outpatient Respiratory Illness: Activity Map
        This week 7 jurisdictions experienced moderate activity and 3 jurisdictions experienced high activity.

        Long-term Care Facilities0.7%

        (Trend )


        of facilities reported
        ≥ 1 influenza-positive test
        among residents this week.


        FluSurv-NET59.5 per 100,000


        cumulative hospitalization rate

        HHS Protect Hospitalizations1,992

        (Trend )


        patients admitted to hospitals with influenza
        this week.


        NCHS Mortality9.4%

        (Trend )


        of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

        Pediatric Deaths5


        deaths were reported this week for a total of
        111 so far this season


        All data are preliminary and may change as more reports are received.

        Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

        A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

        Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

        Key Points
        • Seasonal influenza activity is low nationally.
        • Seven of 10 HHS regions were below their outpatient respiratory illness baselines.
        • The number and weekly rate of flu hospital admissions decreased compared to week 5.
          • Hospitals reported 1,992 influenza hospitalizations to HHS Protect during week 6 compared to 2,183 reported during week 5.
          • The weekly rate of flu hospital admissions in the FluSurv-NET declined again during week 6.
        • Of the 84 influenza A viruses detected and subtyped during week 6, 44.0% were influenza A(H3N2) and 56.0% were influenza A(H1N1).
        • Five influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 111 pediatric flu deaths reported so far this season.
        • CDC estimates that, so far this season, there have been at least 25 million illnesses, 280,000 hospitalizations, and 18,000 deaths from flu.
        • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
        • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (99.9%) have been susceptible to the influenza antiviral oseltamivir.
        • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
        • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
        U.S. Virologic Surveillance


        Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
        Clinical Laboratories


        The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

        No. of specimens tested 84,389 2,394,476
        No. of positive specimens (%) 1,155 (1.4%) 336,953 (14.1%)
        Positive specimens by type
        Influenza A 951 (82.3%) 334,039 (99.1%)
        Influenza B 204 (17.7%) 2,914 (0.9%)


        View Chart Data | View Full Screen
        Public Health Laboratories


        The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
        No. of specimens tested 6,251 172,814
        No. of positive specimens 135 27,073
        Positive specimens by type/subtype
        Influenza A 121 (89.6%) 26,916 (99.4%)
        (H1N1)pdm09 47 (56.0%) 5,545 (24.9%)
        H3N2 37 (44.0%) 16,728 (75.1%)
        H3N2v 0 1 (<0.1%)
        Subtyping not performed 37 4,642
        Influenza B 14 (10.4%) 157 (0.6%)
        Yamagata lineage 0 0
        Victoria lineage 7 (100%) 111 (100%)
        Lineage not performed 7 46


        View Chart Data | View Full Screen

        Additional virologic surveillance information for current and past seasons:
        Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
        Influenza Virus Characterization


        CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

        CDC genetically characterized 1,963 influenza viruses collected since October 2, 2022.
        A/H1 704
        6B.1A 704 (100%) 5a.1 5 (0.7%)
        5a.2 699 (99.3%)
        A/H3 1,220
        3C.2a1b 1,220 (100%) 1a 0
        1b 0
        2a 0
        2a.1 0
        2a.2 1,220 (100%)
        3C.3a 0 3a 0
        B/Victoria 39
        V1A 39 (100%) V1A 0
        V1A.1 0
        V1A.3 4 (10.3%)
        V1A.3a 0
        V1A.3a.1 0
        V1A.3a.2 35 (89.7%)
        B/Yamagata 0
        Y3 0

        CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria, and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell- or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

        Influenza A Viruses
        • A (H1N1)pdm09: Eighty-five A(H1N1)pdm09 viruses were antigenically characterized by HI, and 84 (98.8%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
        • A (H3N2): One hundred and seventy-nine A(H3N2) viruses were antigenically characterized by HINT, and 167 (93.3%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

        Influenza B Viruses
        • B/Victoria: Twelve influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
        • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

        Assessment of Virus Susceptibility to Antiviral Medications

        CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

        Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
        Neuraminidase
        Inhibitors
        Oseltamivir Viruses
        Tested
        1,962 705 1,218 39 0
        Reduced
        Inhibition
        1 (0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
        Highly
        Reduced
        Inhibition
        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
        Peramivir Viruses
        Tested
        1,962 705 1,218 39 0
        Reduced
        Inhibition
        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
        Highly
        Reduced
        Inhibition
        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
        Zanamivir Viruses
        Tested
        1,962 705 1,218 39 0
        Reduced
        Inhibition
        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
        Highly
        Reduced
        Inhibition
        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
        PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
        Tested
        1,901 670 1,192 39 0
        Reduced
        Susceptibility
        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
        One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
        Outpatient Respiratory Illness Surveillance


        The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
        Outpatient Respiratory Illness Visits


        Nationwide during week 6, 2.6% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable (change of ≤ 0.1 percentage point) for the last 4 weeks and remains above the national baseline of 2.5%. Seven of the 10 HHS regions are below their respective baselines, and regions 2, 3, and 9 are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



        * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

        View Chart Data (current season only) | View Full Screen
        Outpatient Respiratory Illness Visits by Age Group


        More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

        The percentage of visits for respiratory illness reported in ILINet remained stable (change of ≤ 0.1 percentage points) for all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, 65+ years) in week 6 compared to week 5.



        View Chart Data | View Full Screen
        Outpatient Respiratory Illness Activity Map


        Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
        Week 6
        (Week ending
        Feb. 11, 2023)
        Week 5
        (Week ending
        Feb. 4, 2023)
        Week 6
        (Week ending
        Feb. 11, 2023)
        Week 5
        (Week ending
        Feb. 4, 2023)
        Very High 0 0 5 3
        High 3 5 28 27
        Moderate 7 5 41 42
        Low 10 11 119 130
        Minimal 35 34 497 484
        Insufficient Data 0 0 239 243



        *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

        Additional information about medically attended visits for ILI for current and past seasons:
        Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
        Long-term Care Facility (LTCF) Surveillance


        LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 6, 98 (0.7%) of 14,358 reporting facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 5.


        View Chart Data | View Full Screen

        Additional information about long-term care facility surveillance:
        Surveillance Methods | Additional Data
        Hospitalization Surveillance

        FluSurv-NET


        The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 13 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

        A total of 17,403 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and February 11, 2023. The weekly hospitalization rate observed in week 6 was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season, which peaked during week 1 (week ending January 6, 2018), and the 2014-2015 season, which peaked during week 52 (week ending December 27, 2014).

        The overall cumulative hospitalization rate was 59.5 per 100,000 population. This cumulative hospitalization rate is the second highest cumulative in-season hospitalization rate observed in week 6 during previous seasons going back to 2010-2011, following the 2017-2018 season. However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for 5 seasons (2014-2015, 2016-2017, 2017-2018, 2018-2019, and 2019-2020 seasons) going back to 2010-2011.

        When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (176.2). Among adults aged 65 and older, rates were highest among adults aged 85 and older (323.3). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (78.4), followed by adults aged 50-64 years (63.9). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (84.4), followed by non-Hispanic American Indian or Alaska Native persons (73.3), non-Hispanic White persons (49.8), Hispanic/Latino persons (45.3), and non-Hispanic Asian/Pacific Islander persons (25).

        Among 17,403 hospitalizations,16,895 (97.1%) were associated with influenza A virus, 335 (1.9%) with influenza B virus, 24 (0.1%) with influenza A virus and influenza B virus co-infection, and 149 (0.9%) with influenza virus for which the type was not determined. Among 3,793 hospitalizations with influenza A subtype information, 2,863 (75.5%) were A(H3N2), and 930 (24.5%) were A(H1N1)pdm09. Based on preliminary data, of the 4,307 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.8% (95% CI: 3.2%-4.4%) also tested positive for SARS-CoV-2.

        Among 3,087 hospitalized adults with information on underlying medical conditions, 2,980 (96.5%) had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 895 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 360 (40.2%) were pregnant. Among 982 hospitalized children with information on underlying medical conditions, 641 (65.3%) had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity, and neurologic disease.



        View Full Screen



        View Full Screen

        Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
        Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
        HHS Protect Hospitalization Surveillance


        Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 6, 1,992 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 5.


        View Chart Data | View Full Screen

        Additional HHS Protect hospitalization surveillance information:
        Surveillance Methods | Additional Data
        Mortality Surveillance

        National Center for Health Statistics (NCHS) Mortality Surveillance


        Based on NCHS mortality surveillance data available on February 16, 2023, 9.4% of the deaths that occurred during the week ending February 11, 2023 (week 6), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage decreased (> 0.3 percentage point change) compared to week 5 and is above the epidemic threshold of 7.3% for this week. Among the 2,398 PIC deaths reported for this week, 998 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 50 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December and has been declining over the past eight weeks. The data presented are preliminary and may change as more data are received and processed.

        View Chart Data | View Full Screen

        Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
        Surveillance Methods | FluView Interactive
        Influenza-Associated Pediatric Mortality


        Five influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 6. The deaths occurred during weeks 44 and 50 of 2022 (the weeks ending November 5, 2022, and December 17, 2022) and during week 2 of 2023 (the week ending January 14, 2023). All five deaths were associated with influenza A viruses. One of the influenza A viruses had subtyping performed; it was an A(H3) virus.

        A total of 111 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

        View Full Screen

        Additional pediatric mortality surveillance information for current and past seasons:
        Surveillance Methods | FluView Interactive
        Trend Indicators


        Increasing:
        Decreasing:
        Stable:
        Indicators Status by System


        Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
        Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
        Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
        HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
        NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

        Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

        Comment


        • #19

          Weekly U.S. Influenza Surveillance Report

          Print
          Updated February 24, 2023

          Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

          Key Updates for Week 7, ending February 18, 2023

          Seasonal influenza activity is low nationally.
          Viruses


          Clinical Lab1.0%

          (Trend )


          positive for influenza
          this week


          Public Health Lab
          The most frequently reported viruses this week were influenza A(H3N2).

          Virus Characterization
          Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
          Illness


          Outpatient Respiratory Illness2.6%

          (Trend )


          of visits to a health care provider this week were for respiratory illness
          (above baseline).


          Outpatient Respiratory Illness: Activity Map
          This week 4 jurisdictions experienced moderate activity and 4 jurisdictions experienced high activity.

          Long-term Care Facilities0.6%

          (Trend )


          of facilities reported
          ≥ 1 influenza-positive test
          among residents this week.


          FluSurv-NET59.7 per 100,000


          cumulative hospitalization rate

          HHS Protect Hospitalizations1,778

          (Trend )


          patients admitted to hospitals with influenza
          this week.


          NCHS Mortality9.0%

          (Trend )


          of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

          Pediatric Deaths4


          deaths were reported this week for a total of
          115 so far this season


          All data are preliminary and may change as more reports are received.

          Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

          A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

          Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

          Key Points
          • Seasonal influenza activity is low nationally.
          • Six of 10 HHS regions were below their outpatient respiratory illness baselines.
          • The number and weekly rate of flu hospital admissions decreased compared to week 6.
            • Hospitals reported 1,778 influenza hospitalizations to HHS Protect during week 7 compared to 2,091 reported during week 6.
            • The weekly rate of flu hospital admissions in the FluSurv-NET declined again during week 7.
          • Of the 53 influenza A viruses detected and subtyped during week 7, 54.7% were influenza A(H3N2) and 45.3% were influenza A(H1N1).
          • Four influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 115 pediatric flu deaths reported so far this season.
          • CDC estimates that, so far this season, there have been at least 25 million illnesses, 280,000 hospitalizations, and 18,000 deaths from flu.
          • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
          • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
          • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
          • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
          U.S. Virologic Surveillance


          Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
          Clinical Laboratories


          The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

          No. of specimens tested 80,331 2,441,426
          No. of positive specimens (%) 833 (1.0%) 333,511 (13.7%)
          Positive specimens by type
          Influenza A 618 (74.2%) 330,235 (99.0%)
          Influenza B 215 (25.8%) 3,276 (1.0%)


          View Chart Data | View Full Screen
          Public Health Laboratories


          The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
          No. of specimens tested 6,020 179,489
          No. of positive specimens 83 27,439
          Positive specimens by type/subtype
          Influenza A 72 (86.7%) 27,255 (99.3%)
          (H1N1)pdm09 24 (45.3%) 5,697 (25.2%)
          H3N2 29 (54.7%) 16,899 (74.8%)
          H3N2v 0 1 (<0.1%)
          Subtyping not performed 19 4,658
          Influenza B 11 (13.3%) 184 (0.7%)
          Yamagata lineage 0 0
          Victoria lineage 6 (100%) 137 (100%)
          Lineage not performed 5 47


          View Chart Data | View Full Screen

          Additional virologic surveillance information for current and past seasons:
          Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
          Influenza Virus Characterization


          CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

          CDC genetically characterized 2,001 influenza viruses collected since October 2, 2022.
          A/H1 704
          6B.1A 704 (100%) 5a.1 5 (0.7%)
          5a.2 699 (99.3%)
          A/H3 1,258
          3C.2a1b 1,258 (100%) 1a 0
          1b 0
          2a 0
          2a.1 0
          2a.2 1,258 (100%)
          3C.3a 0 3a 0
          B/Victoria 39
          V1A 39 (100%) V1A 0
          V1A.1 0
          V1A.3 4 (10.3%)
          V1A.3a 0
          V1A.3a.1 0
          V1A.3a.2 35 (89.7%)
          B/Yamagata 0
          Y3 0

          CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria, and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell- or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

          Influenza A Viruses
          • A (H1N1)pdm09: Eighty-five A(H1N1)pdm09 viruses were antigenically characterized by HI, and 84 (98.8%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
          • A (H3N2): One hundred and seventy-nine A(H3N2) viruses were antigenically characterized by HINT, and 167 (93.3%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

          Influenza B Viruses
          • B/Victoria: Twelve influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
          • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

          Assessment of Virus Susceptibility to Antiviral Medications

          CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

          Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
          Neuraminidase
          Inhibitors
          Oseltamivir Viruses
          Tested
          2,125 756 1,323 46 0
          Reduced
          Inhibition
          1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
          Highly
          Reduced
          Inhibition
          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
          Peramivir Viruses
          Tested
          2,125 756 1,323 46 0
          Reduced
          Inhibition
          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
          Highly
          Reduced
          Inhibition
          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
          Zanamivir Viruses
          Tested
          2,125 756 1,323 46 0
          Reduced
          Inhibition
          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
          Highly
          Reduced
          Inhibition
          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
          PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
          Tested
          2,060 721 1,292 47 0
          Reduced
          Susceptibility
          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
          One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
          Outpatient Respiratory Illness Surveillance


          The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
          Outpatient Respiratory Illness Visits


          Nationwide during week 7, 2.6% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable (change of ≤ 0.1 percentage point) for the last 5 weeks and remains above the national baseline of 2.5%. Six of the 10 HHS regions are below their respective baselines, and regions 2, 3, 7, and 9 are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



          * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

          View Chart Data (current season only) | View Full Screen
          Outpatient Respiratory Illness Visits by Age Group


          More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

          The percentage of visits for respiratory illness reported in ILINet remained stable (change of ≤ 0.1 percentage points) for all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, 65+ years) in week 7 compared to week 6.



          View Chart Data | View Full Screen
          Outpatient Respiratory Illness Activity Map


          Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
          Week 7
          (Week ending
          Feb. 18, 2023)
          Week 6
          (Week ending
          Feb. 11, 2023)
          Week 7
          (Week ending
          Feb. 18, 2023)
          Week 6
          (Week ending
          Feb. 11, 2023)
          Very High 0 0 2 5
          High 4 3 28 28
          Moderate 4 7 43 43
          Low 14 10 111 121
          Minimal 33 35 482 498
          Insufficient Data 0 0 263 234



          *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

          Additional information about medically attended visits for ILI for current and past seasons:
          Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
          Long-term Care Facility (LTCF) Surveillance


          LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 7, 91 (0.6%) of 14,291 reporting facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 6.


          View Chart Data | View Full Screen

          Additional information about long-term care facility surveillance:
          Surveillance Methods | Additional Data
          Hospitalization Surveillance

          FluSurv-NET


          The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 13 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

          A total of 17,466 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and February 18, 2023. The weekly hospitalization rate observed in week 7 was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season, which peaked during week 1 (week ending January 6, 2018), and the 2014-2015 season, which peaked during week 52 (week ending December 27, 2014).

          The overall cumulative hospitalization rate was 59.7 per 100,000 population. This cumulative hospitalization rate is the second highest cumulative in-season hospitalization rate observed in week 7 during previous seasons going back to 2010-2011, following the 2017-2018 season. However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for 5 seasons (2014-2015, 2016-2017, 2017-2018, 2018-2019, and 2019-2020 seasons) going back to 2010-2011.

          When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (177.4). Among adults aged 65 and older, rates were highest among adults aged 85 and older (324.7). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (78.2), followed by adults aged 50-64 years (64.1). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (84.5), followed by non-Hispanic American Indian or Alaska Native persons (73.8), non-Hispanic White persons (50.1), Hispanic/Latino persons (45.5), and non-Hispanic Asian/Pacific Islander persons (25.3).

          Among 17,466 hospitalizations,16,941 (97.0%) were associated with influenza A virus, 351 (2.0%) with influenza B virus, 25 (0.1%) with influenza A virus and influenza B virus co-infection, and 149 (0.9%) with influenza virus for which the type was not determined. Among 3932 hospitalizations with influenza A subtype information, 2,971 (75.6%) were A(H3N2), and 961 (24.4%) were A(H1N1)pdm09. Based on preliminary data, of the11,019 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.9% (95% CI: 3.1%-4.6%) also tested positive for SARS-CoV-2.

          Among 2,485 hospitalized adults with information on underlying medical conditions, 96.7% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 947 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 35.1% were pregnant. Among 1,019 hospitalized children with information on underlying medical conditions, 65.6% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease and obesity.



          View Full Screen



          View Full Screen

          Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
          Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
          HHS Protect Hospitalization Surveillance


          Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 7, 1,778 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 6.


          View Chart Data | View Full Screen

          Additional HHS Protect hospitalization surveillance information:
          Surveillance Methods | Additional Data
          Mortality Surveillance

          National Center for Health Statistics (NCHS) Mortality Surveillance


          Based on NCHS mortality surveillance data available on February 23, 2023, 9.0% of the deaths that occurred during the week ending February 18, 2023 (week 7), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage decreased (> 0.3 percentage point change) compared to week 6 and is above the epidemic threshold of 7.3% for this week. Among the 2,020 PIC deaths reported for this week, 816 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 43 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December, decreased for seven weeks, and has been stable for the past three weeks. The data presented are preliminary and may change as more data are received and processed.

          View Chart Data | View Full Screen

          Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
          Surveillance Methods | FluView Interactive
          Influenza-Associated Pediatric Mortality


          Four influenza-associated pediatric deaths occurring during the 2022-2023 season were reported during week 7. The deaths occurred during weeks 50 and 52 of 2022 (the weeks ending December 17, 2022, and December 31, 2022) and during weeks 2 and 5 of 2023 (the weeks ending January 14, 2023, and February 4, 2023). All four deaths were associated with influenza A viruses. One of the influenza A viruses had subtyping performed; it was an A(H1N1) virus.

          A total of 115 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

          View Full Screen

          Additional pediatric mortality surveillance information for current and past seasons:
          Surveillance Methods | FluView Interactive
          Trend Indicators


          Increasing:
          Decreasing:
          Stable:
          Indicators Status by System


          Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
          Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
          Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
          HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
          NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.


          Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

          Comment


          • #20
            Weekly U.S. Influenza Surveillance Report

            Print
            Updated March 3, 2023

            Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

            Key Updates for Week 8, ending February 25, 2023

            Seasonal influenza activity remains low nationally.
            Viruses


            Clinical Lab1.0%

            (Trend )


            positive for influenza
            this week


            Public Health Lab
            The most frequently reported viruses this week were influenza A(H3N2).

            Virus Characterization
            Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
            Illness


            Outpatient Respiratory Illness2.6%

            (Trend )


            of visits to a health care provider this week were for respiratory illness
            (above baseline).


            Outpatient Respiratory Illness: Activity Map
            This week 1 jurisdiction experienced moderate activity and 5 jurisdictions experienced high activity.

            Long-term Care Facilities0.5%

            (Trend )


            of facilities reported
            ≥ 1 influenza-positive test
            among residents this week.


            FluSurv-NET59.9 per 100,000


            cumulative hospitalization rate

            HHS Protect Hospitalizations1,520

            (Trend )


            patients admitted to hospitals with influenza
            this week.


            NCHS Mortality9.2%

            (Trend )


            of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

            Pediatric Deaths2


            deaths were reported this week for a total of
            117 so far this season


            All data are preliminary and may change as more reports are received.

            Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

            A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

            Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

            Key Points
            • Seasonal influenza activity remains low nationally.
            • Six of 10 HHS regions were below their outpatient respiratory illness baselines.
            • The number and weekly rate of flu hospital admissions decreased compared to week 7.
              • Hospitals reported 1,520 influenza hospitalizations to HHS Protect during week 8 compared to 1,817 reported during week 7.
              • The weekly rate of flu hospital admissions in the FluSurv-NET declined again during week 8.
            • Of the 49 influenza A viruses detected and subtyped during week 8, 63.3% were influenza A(H3N2) and 36.7% were influenza A(H1N1).
            • Two influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 117 pediatric flu deaths reported so far this season.
            • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 18,000 deaths from flu.
            • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
            • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
            • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
            • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
            U.S. Virologic Surveillance


            Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
            Clinical Laboratories


            The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

            No. of specimens tested 70,339 2,524,252
            No. of positive specimens (%) 682 (1.0%) 334,295 (13.2%)
            Positive specimens by type
            Influenza A 538 (78.9%) 330,861 (99.0%)
            Influenza B 144 (21.1%) 3,434 (1.0%)


            View Chart Data | View Full Screen
            Public Health Laboratories


            The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
            No. of specimens tested 5,944 188,098
            No. of positive specimens 73 27,667
            Positive specimens by type/subtype
            Influenza A 67 (91.8%) 27,461 (99.3%)
            (H1N1)pdm09 18 (36.7%) 5,788 (25.4%)
            H3N2 31 (63.3%) 17,002 (74.6%)
            H3N2v 0 1 (<0.1%)
            Subtyping not performed 18 4,670
            Influenza B 6 (8.2%) 206 (0.7%)
            Yamagata lineage 0 0
            Victoria lineage 3 (100%) 159 (100%)
            Lineage not performed 3 47


            View Chart Data | View Full Screen

            Additional virologic surveillance information for current and past seasons:
            Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
            Influenza Virus Characterization


            CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

            CDC genetically characterized 2,289 influenza viruses collected since October 2, 2022.
            A/H1 818
            6B.1A 818 (100%) 5a.1 5 (0.6%)
            5a.2 813 (99.4%)
            A/H3 1,413
            3C.2a1b 1,413 (100%) 1a 0
            1b 0
            2a 0
            2a.1 0
            2a.2 1,413 (100%)
            3C.3a 0 3a 0
            B/Victoria 58
            V1A 58 (100%) V1A 0
            V1A.1 0
            V1A.3 4 (6.9%)
            V1A.3a 0
            V1A.3a.1 0
            V1A.3a.2 54 (93.1%)
            B/Yamagata 0
            Y3 0

            CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria, and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell- or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

            Influenza A Viruses
            • A (H1N1)pdm09: Eighty-five A(H1N1)pdm09 viruses were antigenically characterized by HI, and 84 (99.9%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
            • A (H3N2): One hundred and seventy-nine A(H3N2) viruses were antigenically characterized by HINT, and 167 (93%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

            Influenza B Viruses
            • B/Victoria: Thirteen influenza B/Victoria-lineage virus were antigenically characterized by HI, and thirteen (100%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
            • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

            Assessment of Virus Susceptibility to Antiviral Medications

            CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

            Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
            Neuraminidase
            Inhibitors
            Oseltamivir Viruses
            Tested
            2,312 829 1,425 58 0
            Reduced
            Inhibition
            1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
            Highly
            Reduced
            Inhibition
            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
            Peramivir Viruses
            Tested
            2,312 829 1,425 58 0
            Reduced
            Inhibition
            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
            Highly
            Reduced
            Inhibition
            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
            Zanamivir Viruses
            Tested
            2,312 829 1,425 58 0
            Reduced
            Inhibition
            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
            Highly
            Reduced
            Inhibition
            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
            PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
            Tested
            2,235 788 1,389 58 0
            Reduced
            Susceptibility
            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
            One A(H1N1)pdm09 virus (A/OREGON/63/2022 ) had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
            Outpatient Respiratory Illness Surveillance


            The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
            Outpatient Respiratory Illness Visits


            Nationwide during week 8, 2.6% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable (change of ≤ 0.1 percentage point) for the last 6 weeks and remains above the national baseline of 2.5%. Six of the 10 HHS regions are below their respective baselines, regions 2 and 9 are above their respective baselines, and regions 3 and 8 are at their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



            * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

            View Chart Data (current season only) | View Full Screen
            Outpatient Respiratory Illness Visits by Age Group


            More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

            The percentage of visits for respiratory illness reported in ILINet remained stable (change of ≤ 0.1 percentage points) for four age groups (5-24 years, 25-49 years, 50-64 years, 65+ years) and increased in the 0-4 years age group in week 8 compared to week 7.



            View Chart Data | View Full Screen
            Outpatient Respiratory Illness Activity Map


            Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
            Week 8
            (Week ending
            Feb. 25, 2023)
            Week 7
            (Week ending
            Feb. 18, 2023)
            Week 8
            (Week ending
            Feb. 25, 2023)
            Week 7
            (Week ending
            Feb. 18, 2023)
            Very High 0 0 3 3
            High 5 4 20 29
            Moderate 1 5 36 45
            Low 8 15 118 111
            Minimal 41 31 494 493
            Insufficient Data 0 0 258 248



            *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

            Additional information about medically attended visits for ILI for current and past seasons:
            Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
            Long-term Care Facility (LTCF) Surveillance


            LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 8, 67 (0.5%) of 14,313 reporting facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 7.


            View Chart Data | View Full Screen

            Additional information about long-term care facility surveillance:
            Surveillance Methods | Additional Data
            Hospitalization Surveillance

            FluSurv-NET


            The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

            A total of 17,526 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022 and February 25, 2023. The weekly hospitalization rate observed in week 8 was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

            The overall cumulative hospitalization rate was 59.9 per 100,000 population. This cumulative hospitalization rate is the second highest cumulative in-season hospitalization rate observed in week 8 during previous seasons going back to 2010-2011, following the 2017-2018 season. However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for 5 seasons (2014-2015, 2016-2017, 2017-2018, 2018-2019, and 2019-2020 seasons) going back to 2010-2011.

            When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (178.1). Among adults aged 65 and older, rates were highest among adults aged 85 and older (325.8). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (78.2) followed by adults aged 50-64 years (64.4). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (84.9), followed by non-Hispanic American Indian or Alaska Native persons (73.3), non-Hispanic White persons (50.4), Hispanic/Latino persons (45.8), and non-Hispanic Asian/Pacific Islander persons (25.6).

            Among 17,526 hospitalizations,16,985 (96.9%) were associated with influenza A virus, 368 (2.1%) with influenza B virus, 25 (0.1%) with influenza A virus and influenza B virus co-infection, and 148 (0.8%) with influenza virus for which the type was not determined. Among 4,035 hospitalizations with influenza A subtype information, 3,047 (75.5%) were A(H3N2), and 988 (24.5%) were A(H1N1)pdm09. Based on preliminary data, of the 11,939 laboratory-confirmed influenza-associated hospitalizations with more complete data, 4.0% (95% CI: 3.2%-4.8%) also tested positive for SARS-CoV-2.

            Among 2,743 hospitalized adults with information on underlying medical conditions, 96.7% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 988 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 35.1% were pregnant. Among 1,064 hospitalized children with information on underlying medical conditions, 65.6% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity, and neurologic disease.



            View Full Screen



            View Full Screen

            Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
            Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
            HHS Protect Hospitalization Surveillance


            Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 8, 1,520 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 7.


            View Chart Data | View Full Screen

            Additional HHS Protect hospitalization surveillance information:
            Surveillance Methods | Additional Data
            Mortality Surveillance

            National Center for Health Statistics (NCHS) Mortality Surveillance


            Based on NCHS mortality surveillance data available on March 2, 2023, 9.2% of the deaths that occurred during the week ending February 25, 2023 (week 8), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remains stable (< 0.3 percentage point change) compared to week 7 and is above the epidemic threshold of 7.3% for this week. Among the 2,202 PIC deaths reported for this week, 916 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 34 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December, decreased for seven weeks, and has been stable for the past four weeks. The data presented are preliminary and may change as more data are received and processed.

            View Chart Data | View Full Screen

            Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
            Surveillance Methods | FluView Interactive
            Influenza-Associated Pediatric Mortality


            Two influenza-associated pediatric deaths occurring during the 2022-2023 season were reported during week 8. The deaths occurred during weeks 48 and 49 of 2022 (the weeks ending December 3, 2022, and December 10, 2022). Both deaths were associated with influenza A viruses. One of the influenza A viruses had subtyping performed; it was an A(H3N2) virus.

            A total of 117 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

            View Full Screen

            Additional pediatric mortality surveillance information for current and past seasons:
            Surveillance Methods | FluView Interactive
            Trend Indicators


            Increasing:
            Decreasing:
            Stable:
            Indicators Status by System


            Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
            Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
            Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
            HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
            NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.


            Additional National and International Influenza Surveillance Information


            FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.

            National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.

            U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.

            Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

            Comment


            • #21
              Weekly U.S. Influenza Surveillance Report

              Print
              Updated March 10, 2023

              Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

              Key Updates for Week 9, ending March 4, 2023

              Seasonal influenza activity remains low nationally.
              Viruses


              Clinical Lab0.9%

              (Trend )


              positive for influenza
              this week


              Public Health Lab
              The most frequently reported viruses this week were influenza A(H3N2).

              Virus Characterization
              Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
              Illness


              Outpatient Respiratory Illness2.4%

              (Trend )


              of visits to a health care provider this week were for respiratory illness
              (below baseline).


              Outpatient Respiratory Illness: Activity Map
              This week 4 jurisdictions experienced moderate activity and 3 jurisdictions experienced high activity.

              Long-term Care Facilities0.5%

              (Trend )


              of facilities reported
              ≥ 1 influenza-positive test
              among residents this week.


              FluSurv-NET60.0 per 100,000


              cumulative hospitalization rate

              HHS Protect Hospitalizations1,418

              (Trend )


              patients admitted to hospitals with influenza
              this week.


              NCHS Mortality8.9%

              (Trend )


              of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

              Pediatric Deaths8


              deaths were reported this week for a total of
              125 so far this season


              All data are preliminary and may change as more reports are received.

              Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

              A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

              Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

              Key Points
              • Seasonal influenza activity remains low nationally.
              • Nationally, outpatient respiratory illness is now below baseline, and eight of 10 HHS regions are below their respective baselines.
              • The number and weekly rate of flu hospital admissions decreased compared to week 8.
                • Hospitals reported 1,418 influenza hospitalizations to HHS Protect during week 9 compared to 1,644 reported during week 8.
                • The weekly rate of flu hospital admissions in the FluSurv-NET declined again during week 9.
              • Of the 51 influenza A viruses detected and subtyped during week 9, 55% were influenza A(H3N2) and 45% were influenza A(H1N1).
              • Eight influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 125 pediatric flu deaths reported so far this season.
              • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 18,000 deaths from flu.
              • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
              • Recommendations for U.S. flu vaccine composition for the 2023-2024 season have been made and include an update to the influenza A(H1N1)pdm09 component.
              • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
              • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
              • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
              U.S. Virologic Surveillance


              Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
              Clinical Laboratories


              The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

              No. of specimens tested 64,083 2,609,725
              No. of positive specimens (%) 565 (0.9%) 335,167 (12.8%)
              Positive specimens by type
              Influenza A 396 (70.1%) 331,473 (98.9%)
              Influenza B 169 (29.9%) 3,694 (1.1%)


              View Chart Data | View Full Screen
              Public Health Laboratories


              The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
              No. of specimens tested 6,414 195,177
              No. of positive specimens 88 27,866
              Positive specimens by type/subtype
              Influenza A 72 (81.8%) 27,630 (99.2%)
              (H1N1)pdm09 23 (45.1%) 5,880 (25.6%)
              H3N2 28 (54.9%) 17,127 (74.4%)
              H3N2v 0 1 (<0.1%)
              Subtyping not performed 21 4,622
              Influenza B 16 (18.2%) 236 (0.8%)
              Yamagata lineage 0 0
              Victoria lineage 7 (100%) 178 (100%)
              Lineage not performed 9 58


              View Chart Data | View Full Screen

              Additional virologic surveillance information for current and past seasons:
              Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
              Influenza Virus Characterization


              CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

              CDC genetically characterized 2,320 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2 but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2 and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
              A/H1 829
              6B.1A.5a 829 (100%) 1 5 (0.6%)
              2a 129 (15.6%)
              2a.1 695 (83.8%)
              A/H3 1,427
              3C.2a1b.2a 1,427 (100%) 2a 25 (1.8%)
              2a.1 164 (11.5%)
              2a.1b 102 (7.1%)
              2a.2c 0 (0%)
              2a.3 41 (2.9%)
              2a.3a 3 (0.2%)
              2a.3a.1 43 (3.0%)
              2a.3b 8 (0.6%)
              2b 1,041 (73.0%)
              B/Victoria 64
              V1A 64 (100%) 3 4 (6.3%)
              3a.2 60 (93.8%)
              B/Yamagata 0
              Y3 0 Y3 0 (0%)

              CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

              Influenza A Viruses
              • A (H1N1)pdm09: Eighty-five A(H1N1)pdm09 viruses were antigenically characterized by HI, and 84 (99.9%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
              • A (H3N2): One hundred and seventy-nine A(H3N2) viruses were antigenically characterized by HINT, and 167 (93%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

              Influenza B Viruses
              • B/Victoria: Thirteen influenza B/Victoria-lineage virus were antigenically characterized by HI, and thirteen (100%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
              • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.



              2023-2024 Influenza Season – U.S. Influenza Vaccine Composition:

              The World Health Organization (WHO) has recommended the Northern Hemisphere 2023-2024 influenza vaccine composition, and the Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) subsequently made the influenza vaccine composition recommendation for the United States. Both agencies recommend that influenza vaccines contain the following:

              Egg-based vaccines
              • an A/Victoria/4897/2022 (H1N1)pdm09-like virus
              • an A/Darwin/9/2021 (H3N2)-like virus
              • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus
              • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus

              Cell- or recombinant-based vaccines
              • an A/Wisconsin/67/2022 (H1N1)pdm09-like virus
              • an A/Darwin/6/2021 (H3N2)-like virus
              • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus
              • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus

              The A(H1N1)pdm09 recommendation represents an update to the 2022-2023 Northern Hemisphere vaccines. These vaccine recommendations were based on several factors, including global influenza virologic and epidemiologic surveillance, genetic characterization, antigenic characterization, and the candidate vaccine viruses that are available for production.

              Assessment of Virus Susceptibility to Antiviral Medications

              CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

              Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
              Neuraminidase
              Inhibitors
              Oseltamivir Viruses
              Tested
              2,380 854 1,458 68 0
              Reduced
              Inhibition
              1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
              Highly
              Reduced
              Inhibition
              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
              Peramivir Viruses
              Tested
              2,380 854 1,458 68 0
              Reduced
              Inhibition
              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
              Highly
              Reduced
              Inhibition
              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
              Zanamivir Viruses
              Tested
              2,380 854 1,458 68 0
              Reduced
              Inhibition
              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
              Highly
              Reduced
              Inhibition
              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
              PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
              Tested
              2,303 811 1,424 68 0
              Reduced
              Susceptibility
              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
              One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
              Outpatient Respiratory Illness Surveillance


              The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
              Outpatient Respiratory Illness Visits


              Nationwide during week 9, 2.4% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has decreased compared to week 8 and is below the national baseline of 2.5%. Eight of the 10 HHS regions are below their respective baselines; regions 2 and 9 are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



              * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

              View Chart Data (current season only) | View Full Screen
              Outpatient Respiratory Illness Visits by Age Group


              More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

              The percentage of visits for respiratory illness reported in ILINet remained stable (change of ≤ 0.1 percentage points) for four age groups (5-24 years, 25-49 years, 50-64 years, 65+ years) and decreased in the 0-4 years age group in week 9 compared to week 8.



              View Chart Data | View Full Screen
              Outpatient Respiratory Illness Activity Map


              Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
              Week 9
              (Week ending
              Mar. 4, 2023)
              Week 8
              (Week ending
              Feb. 25, 2023)
              Week 9
              (Week ending
              Mar. 4, 2023)
              Week 8
              (Week ending
              Feb. 25, 2023)
              Very High 0 0 1 4
              High 3 5 21 20
              Moderate 4 1 34 36
              Low 10 9 101 119
              Minimal 38 40 534 513
              Insufficient Data 0 0 238 237



              *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

              Additional information about medically attended visits for ILI for current and past seasons:
              Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
              Long-term Care Facility (LTCF) Surveillance


              LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 9, 67 (0.5%) of 14,305 reporting facilities reported at least one influenza positive test among their residents. This percentage remains stable compared to week 8.


              View Chart Data | View Full Screen

              Additional information about long-term care facility surveillance:
              Surveillance Methods | Additional Data
              Hospitalization Surveillance

              FluSurv-NET


              The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

              A total of 17,565 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and March 4, 2023. The weekly hospitalization rate observed in week 9 was 0.1 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season, which peaked during week 1 (week ending January 6, 2018), and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

              The overall cumulative hospitalization rate was 60.0 per 100,000 population. This cumulative hospitalization rate is the second highest cumulative in-season hospitalization rate observed in week 9 during previous seasons going back to 2010-2011, following the 2017-2018 season. However, this in-season cumulative hospitalization rate is similar to the end-of-season hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the end-of-season hospitalization rate for the 2017-2018 season, going back to 2010-2011.

              When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (178.6). Among adults aged 65 and older, rates were highest among adults aged 85 and older (326.8). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (78.4), followed by adults aged 50-64 years (64.6). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (85.1), followed by non-Hispanic American Indian or Alaska Native persons (69.4), non-Hispanic White persons (50.6), Hispanic/Latino persons (46.1), and non-Hispanic Asian/Pacific Islander persons (25.8).

              Among 17,565 hospitalizations, 17,007 (96.8%) were associated with influenza A virus, 380 (2.2%) with influenza B virus, 26 (0.1%) with influenza A virus and influenza B virus co-infection, and 152 (0.9%) with influenza virus for which the type was not determined. Among 4,076 hospitalizations with influenza A subtype information, 3,081 (75.6%) were A(H3N2), and 995 (24.4%) were A(H1N1)pdm09. Based on preliminary data, of the 12,746 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.9% (95% CI: 3.1%-4.7%) also tested positive for SARS-CoV-2.

              Among 2,912 hospitalized adults with information on underlying medical conditions, 96.9% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 786 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 37.8% were pregnant. Among 1,034 hospitalized children with information on underlying medical conditions, 63.7% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity, and neurologic disease.



              View Full Screen



              View Full Screen

              Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
              Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
              HHS Protect Hospitalization Surveillance


              Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 9, 1,418 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 8.


              View Chart Data | View Full Screen

              Additional HHS Protect hospitalization surveillance information:
              Surveillance Methods | Additional Data
              Mortality Surveillance

              National Center for Health Statistics (NCHS) Mortality Surveillance


              Based on NCHS mortality surveillance data available on March 9, 2023, 8.9% of the deaths that occurred during the week ending March 4, 2023 (week 9), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remained stable (< 0.3 percentage point change) compared to week 8 and is above the epidemic threshold of 7.3% for this week. Among the 2,172 PIC deaths reported for this week, 876 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 22 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December, decreased for seven weeks, and has been stable at low levels for the past five weeks. The data presented are preliminary and may change as more data are received and processed.

              View Chart Data | View Full Screen

              Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
              Surveillance Methods | FluView Interactive
              Influenza-Associated Pediatric Mortality


              Eight influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 9. The deaths occurred between week 43 of 2022 (the week ending October 29, 2022) and week 8 of 2023 (the week ending February 25, 2023). All eight deaths were associated with influenza A viruses. Four of the influenza A viruses had subtyping performed; all four were A(H3) viruses.

              A total of 125 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

              View Full Screen

              Additional pediatric mortality surveillance information for current and past seasons:
              Surveillance Methods | FluView Interactive
              Trend Indicators


              Increasing:
              Decreasing:
              Stable:
              Indicators Status by System


              Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
              Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
              Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
              HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
              NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.


              Additional National and International Influenza Surveillance Information


              FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.

              National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.

              U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.

              Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

              Comment


              • #22
                Weekly U.S. Influenza Surveillance Report

                Print
                Updated March 17, 2023

                Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                Key Updates for Week 10, ending March 11, 2023

                Seasonal influenza activity remains low nationally.
                Viruses


                Clinical Lab1.0%

                (Trend )


                positive for influenza
                this week


                Public Health Lab
                The most frequently reported viruses this week were influenza A(H1N1).

                Virus Characterization
                Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
                Illness


                Outpatient Respiratory Illness2.4%

                (Trend )


                of visits to a health care provider this week were for respiratory illness
                (below baseline).


                Outpatient Respiratory Illness: Activity Map
                This week 4 jurisdictions experienced moderate activity and 2 jurisdictions experienced high activity.

                Long-term Care Facilities0.5%

                (Trend )


                of facilities reported
                ≥ 1 influenza-positive test
                among residents this week.


                FluSurv-NET60.4 per 100,000


                cumulative hospitalization rate

                HHS Protect Hospitalizations1,387

                (Trend )


                patients admitted to hospitals with influenza
                this week.


                NCHS Mortality8.6%

                (Trend )


                of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                Pediatric Deaths7


                deaths were reported this week for a total of
                132 so far this season


                All data are preliminary and may change as more reports are received.

                Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                Key Points
                • Seasonal influenza activity remains low nationally.
                • Nationally, outpatient respiratory illness is now below baseline, and six of 10 HHS regions are below their respective baselines.
                • The number and weekly rate of flu hospital admissions has remained stable compared to week 9.
                • Of the 35 influenza A viruses detected and subtyped during week, 34% were influenza A(H3N2) and 66% were influenza A(H1N1).
                • Seven influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 132 pediatric flu deaths reported so far this season.
                • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 18,000 deaths from flu.
                • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
                U.S. Virologic Surveillance


                Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
                Clinical Laboratories


                The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

                No. of specimens tested 66,138 2,695,361
                No. of positive specimens (%) 666 (1.0%) 336,008 (12.5%)
                Positive specimens by type
                Influenza A 441 (66.2%) 332,059 (98.8%)
                Influenza B 225 (33.8%) 3,949 (1.2%)


                View Chart Data | View Full Screen
                Public Health Laboratories


                The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                No. of specimens tested 6,258 201,965
                No. of positive specimens 79 28,045
                Positive specimens by type/subtype
                Influenza A 58 (73.4%) 27,763 (99.0%)
                (H1N1)pdm09 23 (65.7%) 5,984 (25.8%)
                H3N2 12 (34.3%) 17,209 (74.2%)
                H3N2v 0 1 (<0.1%)
                Subtyping not performed 23 4,569
                Influenza B 21 (26.6%) 282 (1.0%)
                Yamagata lineage 0 0
                Victoria lineage 9 (100%) 213(100%)
                Lineage not performed 12 69


                View Chart Data | View Full Screen

                Additional virologic surveillance information for current and past seasons:
                Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
                Influenza Virus Characterization


                CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                CDC genetically characterized 2,459 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2 but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2 and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                A/H1 885
                6B.1A.5a 885 (100%) 1 5 (0.6%)
                2a 137 (15.6%)
                2a.1 743 (84.0%)
                A/H3 1,500
                3C.2a1b.2a 1,500 (100%) 2a 25 (1.7%)
                2a.1 176 (11.5%)
                2a.1b 113 (7.5%)
                2a.2c 0 (0%)
                2a.3 45 (3.0%)
                2a.3a 3 (0.2%)
                2a.3a.1 46 (3.1%)
                2a.3b 9 (0.6%)
                2b 1,083 (72.2%)
                B/Victoria 74
                V1A 74 (100%) 3 4 (5.4%)
                3a.2 70 (94.6%)
                B/Yamagata 0
                Y3 0 Y3 0 (0%)

                CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                Influenza A Viruses
                • A (H1N1)pdm09: Ninety-eight A(H1N1)pdm09 viruses were antigenically characterized by HI, and 96 (98%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
                • A (H3N2): One hundred and seventy-nine A(H3N2) viruses were antigenically characterized by HINT, and 167 (93%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                Influenza B Viruses
                • B/Victoria: Thirteen influenza B/Victoria-lineage virus were antigenically characterized by HI, and thirteen (100%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                Assessment of Virus Susceptibility to Antiviral Medications

                CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                Neuraminidase
                Inhibitors
                Oseltamivir Viruses
                Tested
                2,456 887 1,495 74 0
                Reduced
                Inhibition
                1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                Highly
                Reduced
                Inhibition
                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                Peramivir Viruses
                Tested
                2,456 887 1,495 74 0
                Reduced
                Inhibition
                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                Highly
                Reduced
                Inhibition
                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                Zanamivir Viruses
                Tested
                2,456 887 1,495 74 0
                Reduced
                Inhibition
                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                Highly
                Reduced
                Inhibition
                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                Tested
                2,378 844 1,460 74 0
                Reduced
                Susceptibility
                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
                Outpatient Respiratory Illness Surveillance


                The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
                Outpatient Respiratory Illness Visits


                Nationwide during week 10, 2.4% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable compared to week 9 and is below the national baseline of 2.5%. Six of the 10 HHS regions are below their respective baselines; regions 2, 3, 7, and 9 are at or above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



                * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                View Chart Data (current season only) | View Full Screen
                Outpatient Respiratory Illness Visits by Age Group


                More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                The percentage of visits for respiratory illness reported in ILINet increased (change of > 0.1 percentage points) in the 0-4 years age group and remained stable (change of ≤ 0.1 percentage points) for four age groups (5-24 years, 25-49 years, 50-64 years, 65+ years) in week 10 compared to week 9.



                View Chart Data | View Full Screen
                Outpatient Respiratory Illness Activity Map


                Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                Week 10
                (Week ending
                Mar. 11, 2023)
                Week 9
                (Week ending
                Mar. 4, 2023)
                Week 10
                (Week ending
                Mar. 11, 2023)
                Week 9
                (Week ending
                Mar. 4, 2023)
                Very High 0 0 1 2
                High 2 3 18 22
                Moderate 4 4 31 33
                Low 6 8 98 104
                Minimal 43 40 530 534
                Insufficient Data 0 0 251 234



                *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                Additional information about medically attended visits for ILI for current and past seasons:
                Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
                Long-term Care Facility (LTCF) Surveillance


                LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 10, 73 (0.5%) of 14,389 reporting facilities reported at least one influenza positive test among their residents. This percentage remained stable compared to week 9.


                View Chart Data | View Full Screen

                Additional information about long-term care facility surveillance:
                Surveillance Methods | Additional Data
                Hospitalization Surveillance

                FluSurv-NET


                The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

                A total of 17,667 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and March 11, 2023. The weekly hospitalization rate observed in week 10 was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

                The overall cumulative hospitalization rate was 60.4 per 100,000 population. This cumulative hospitalization rate is the second highest cumulative in-season hospitalization rate observed in week 10 during previous seasons going back to 2010-2011, following the 2017-2018 season. However, this in-season cumulative hospitalization rate is similar to the end-of-season hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the end-of-season hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (179.5). Among adults aged 65 and older, rates were highest among adults aged 85 and older (329.4). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (78.7) followed by adults aged 50-64 years (65.2). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (85.3), followed by non-Hispanic American Indian or Alaska Native persons (72.8), non-Hispanic White persons (50.8), Hispanic/Latino persons (46.6), and non-Hispanic Asian/Pacific Islander persons (26.3).

                Among 17,667 hospitalizations,17,090 (96.7%) were associated with influenza A virus, 408 (2.3%) with influenza B virus, 26 (0.1%) with influenza A virus and influenza B virus co-infection, and 143 (0.8%) with influenza virus for which the type was not determined. Among 4,145 hospitalizations with influenza A subtype information, 3,125 (75.4%) were A(H3N2), and 1,020 (24.6%) were A(H1N1)pdm09. Based on preliminary data, of the 13,358 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.8% (95% CI: 3.0%-4.5%) also tested positive for SARS-CoV-2.

                Among 2,941 hospitalized adults with information on underlying medical conditions, 96.6% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 824 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 37.8% were pregnant. Among 1,062 hospitalized children with information on underlying medical conditions, 62.2% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease, and obesity.



                View Full Screen



                View Full Screen

                Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
                HHS Protect Hospitalization Surveillance


                Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 10, 1,387 patients with laboratory-confirmed influenza were admitted to a hospital. The number of patients admitted to a hospital with laboratory-confirmed influenza remained stable compared to week 9.


                View Chart Data | View Full Screen

                Additional HHS Protect hospitalization surveillance information:
                Surveillance Methods | Additional Data
                Mortality Surveillance

                National Center for Health Statistics (NCHS) Mortality Surveillance


                Based on NCHS mortality surveillance data available on March 16, 2023, 8.6% of the deaths that occurred during the week ending March 11, 2023 (week 10), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remained stable (< 0.3 percentage point change) compared to week 9 and is above the epidemic threshold of 7.2% for this week. Among the 2,077 PIC deaths reported for this week, 797 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 19 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December, decreased for seven weeks, and has been stable at low levels for the past six weeks. The data presented are preliminary and may change as more data are received and processed.

                View Chart Data | View Full Screen

                Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                Surveillance Methods | FluView Interactive
                Influenza-Associated Pediatric Mortality


                Seven influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 10. The deaths occurred between week 47 of 2022 (the week ending November 26, 2022) and week 9 of 2023 (the week ending March 4, 2023). All seven deaths were associated with influenza A viruses. Four of the influenza A viruses had subtyping performed; one was an A(H1N1) virus and three were A(H3) viruses.

                A total of 132 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

                View Full Screen

                Additional pediatric mortality surveillance information for current and past seasons:
                Surveillance Methods | FluView Interactive
                Trend Indicators


                Increasing:
                Decreasing:
                Stable:
                Indicators Status by System


                Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.


                Additional National and International Influenza Surveillance Information


                FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.

                National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.

                U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.

                Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                Comment


                • #23
                  Weekly U.S. Influenza Surveillance Report


                  Print
                  Updated March 31, 2023

                  Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                  Key Updates for Week 12, ending March 25, 2023

                  Seasonal influenza activity remains low nationally.
                  Viruses


                  Clinical Lab0.9%

                  (Trend )


                  positive for influenza
                  this week


                  Public Health Lab
                  The most frequently reported viruses this week were influenza A(H3N2).

                  Virus Characterization
                  Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
                  Illness


                  Outpatient Respiratory Illness2.3%

                  (Trend )


                  of visits to a health care provider this week were for respiratory illness
                  (below baseline).


                  Outpatient Respiratory Illness: Activity Map
                  This week 3 jurisdictions experienced moderate activity and 2 jurisdictions experienced high activity.

                  Long-term Care Facilities0.4%

                  (Trend )


                  of facilities reported
                  ≥ 1 influenza-positive test
                  among residents this week.


                  FluSurv-NET60.8 per 100,000


                  cumulative hospitalization rate

                  HHS Protect Hospitalizations1,222

                  (Trend )


                  patients admitted to hospitals with influenza
                  this week.


                  NCHS Mortality8.3%

                  (Trend )


                  of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                  Pediatric Deaths4


                  deaths were reported this week for a total of
                  138 so far this season


                  All data are preliminary and may change as more reports are received.

                  Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                  A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                  Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                  Key Points
                  • Seasonal influenza activity remains low nationally.
                  • Nationally, outpatient respiratory illness is below baseline, and eight of 10 HHS regions are below their respective baselines.
                  • The number and weekly rate of flu hospital admissions remain low.
                  • During week 12, 67.2% of viruses reported by public health laboratories were influenza A and 32.8% were influenza B. Of the 34 influenza A viruses detected and subtyped during week 12, 58.8% were influenza A(H3N2) and 41.2% were influenza A(H1N1).
                  • Four influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 138 pediatric flu deaths reported so far this season.
                  • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 18,000 deaths from flu.
                  • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                  • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                  • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                  • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
                  U.S. Virologic Surveillance


                  Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
                  Clinical Laboratories


                  The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

                  No. of specimens tested 66,542 2,864,095
                  No. of positive specimens (%) 626 (0.9%) 337,643 (11.8%)
                  Positive specimens by type
                  Influenza A 386 (61.7%) 333,076 (98.6%)
                  Influenza B 240 (38.3%) 4,567 (1.4%)


                  View Chart Data | View Full Screen
                  Public Health Laboratories


                  The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                  No. of specimens tested 5,686 214,894
                  No. of positive specimens 64 28,345
                  Positive specimens by type/subtype
                  Influenza A 43 (67.2%) 28,009 (98.8%)
                  (H1N1)pdm09 14 (41.2%) 6,153 (26.1%)
                  H3N2 20 (58.8%) 17,380 (73.9%)
                  H3N2v 0 1 (<0.1%)
                  Subtyping not performed 9 4,475
                  Influenza B 21 (32.8%) 336 (1.2%)
                  Yamagata lineage 0 0
                  Victoria lineage 6 (100%) 242 (100%)
                  Lineage not performed 15 94


                  View Chart Data | View Full Screen

                  Additional virologic surveillance information for current and past seasons:
                  Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
                  Influenza Virus Characterization


                  CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                  CDC genetically characterized 2,560 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2 but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2 and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                  A/H1 925
                  6B.1A.5a 925 (100%) 1 5 (0.6%)
                  2a 139 (15.0%)
                  2a.1 781 (84.4%)
                  A/H3 1,542
                  3C.2a1b.2a 1,542 (100%) 2a 25 (1.6%)
                  2a.1 179 (11.6%)
                  2a.1b 115 (7.5%)
                  2a.2c 0 (0%)
                  2a.3 46 (3.0%)
                  2a.3a 3 (0.2%)
                  2a.3a.1 47 (3.0%)
                  2a.3b 10 (0.6%)
                  2b 1,117 (72.4%)
                  B/Victoria 93
                  V1A 93 (100%) 3 4 (4.3%)
                  3a.2 89 (95.7%)
                  B/Yamagata 0
                  Y3 0 Y3 0 (0%)

                  CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                  Influenza A Viruses
                  • A (H1N1)pdm09: Ninety-eight A(H1N1)pdm09 viruses were antigenically characterized by HI, and 96 (98%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
                  • A (H3N2): One hundred and eighty A(H3N2) viruses were antigenically characterized by HINT, and 168 (93%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                  Influenza B Viruses
                  • B/Victoria: Thirteen influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                  • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                  Assessment of Virus Susceptibility to Antiviral Medications

                  CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                  Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                  Neuraminidase
                  Inhibitors
                  Oseltamivir Viruses
                  Tested
                  2,542 923 1,538 81 0
                  Reduced
                  Inhibition
                  1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                  Highly
                  Reduced
                  Inhibition
                  0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                  Peramivir Viruses
                  Tested
                  2,542 923 1,538 81 0
                  Reduced
                  Inhibition
                  0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                  Highly
                  Reduced
                  Inhibition
                  0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                  Zanamivir Viruses
                  Tested
                  2,542 923 1,538 81 0
                  Reduced
                  Inhibition
                  0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                  Highly
                  Reduced
                  Inhibition
                  0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                  PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                  Tested
                  2,476 883 1,502 91 0
                  Reduced
                  Susceptibility
                  0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                  One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
                  Outpatient Respiratory Illness Surveillance


                  The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
                  Outpatient Respiratory Illness Visits


                  Nationwide during week 12, 2.3% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable compared to week 11 and is below the national baseline of 2.5%. Eight of the 10 HHS regions are below their respective baselines; regions 2 and 9 are at or above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



                  * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                  View Chart Data (current season only) | View Full Screen
                  Outpatient Respiratory Illness Visits by Age Group


                  More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                  The percentage of visits for respiratory illness reported in ILINet decreased for one age group (0-4 years) and remained stable (change of ≤ 0.1 percentage points) for the remaining age groups (5-24 years, 25-49 years, 50-64 years, 65+ years) in week 12 compared to week 11.



                  View Chart Data | View Full Screen
                  Outpatient Respiratory Illness Activity Map


                  Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                  Week 12
                  (Week ending
                  Mar. 25, 2023)
                  Week 11
                  (Week ending
                  Mar. 18, 2023)
                  Week 12
                  (Week ending
                  Mar. 25, 2023)
                  Week 11
                  (Week ending
                  Mar. 18, 2023)
                  Very High 0 0 1 2
                  High 2 3 18 23
                  Moderate 3 3 30 29
                  Low 4 6 85 94
                  Minimal 45 43 535 548
                  Insufficient Data 1 0 260 233



                  *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                  Additional information about medically attended visits for ILI for current and past seasons:
                  Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
                  Long-term Care Facility (LTCF) Surveillance


                  LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 12, 58 (0.40%) of 14,345 reporting facilities reported at least one influenza positive test among their residents. This percentage remained stable compared to week 11.


                  View Chart Data | View Full Screen

                  Additional information about long-term care facility surveillance:
                  Surveillance Methods | Additional Data
                  Hospitalization Surveillance

                  FluSurv-NET


                  The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

                  A total of 17,788 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and March 25, 2023. The weekly hospitalization rate observed in week 12 was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

                  The overall cumulative hospitalization rate was 60.8 per 100,000 population. This cumulative hospitalization rate is the third highest cumulative in-season hospitalization rate observed in week 12 during previous seasons going back to 2010-2011, following the 2017-2018 season. However, this in-season cumulative hospitalization rate is similar to the end-of-season hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the end-of-season hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                  When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (180.7). Among adults aged 65 and older, rates were highest among adults aged 85 and older (332.1). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (79.6) followed by adults aged 50-64 years (65.6). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (85.9), followed by non-Hispanic American Indian or Alaska Native persons (76.8), Hispanic/Latino persons (52.1), non-Hispanic White persons (51.7), and non-Hispanic Asian/Pacific Islander persons (26.5).

                  Among 17,788 hospitalizations, 17,131 (96.3%) were associated with influenza A virus, 485 (2.7%) with influenza B virus, 29 (0.2%) with influenza A virus and influenza B virus co-infection, and 143 (0.8%) with influenza virus for which the type was not determined. Among 4,332 hospitalizations with influenza A subtype information, 3,258 (75.2%) were A(H3N2), and 1,074 (24.8%) were A(H1N1)pdm09. Based on preliminary data, of the 14,717 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.8% (95% CI: 3.1%-4.5%) also tested positive for SARS-CoV-2.

                  Among 3,481 hospitalized adults with information on underlying medical conditions, 97.0% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 1,210 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 36.7% were pregnant. Among 1,263 hospitalized children with information on underlying medical conditions, 65.8% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease, and obesity.



                  View Full Screen



                  View Full Screen

                  Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                  Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
                  HHS Protect Hospitalization Surveillance


                  Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 12, 1,222 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 11.


                  View Chart Data | View Full Screen

                  Additional HHS Protect hospitalization surveillance information:
                  Surveillance Methods | Additional Data
                  Mortality Surveillance

                  National Center for Health Statistics (NCHS) Mortality Surveillance


                  Based on NCHS mortality surveillance data available on March 30, 2023, 8.3% of the deaths that occurred during the week ending March 25, 2023 (week 12), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remained stable (< 0.3 percentage point change) compared to week 11 and is above the epidemic threshold of 7.1% for this week. Among the 2,004 PIC deaths reported for this week, 710 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 21 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December, decreased for eight weeks, and has been stable at low levels for the past seven weeks. The data presented are preliminary and may change as more data are received and processed.

                  View Chart Data | View Full Screen

                  Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                  Surveillance Methods | FluView Interactive
                  Influenza-Associated Pediatric Mortality


                  Four influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 12. The deaths occurred during weeks 42, 50, and 51 of 2022 (the weeks ending October 22, December 17, and December 24 of 2022), and during week 11 of 2023 (the week ending March 18, 2023). All four deaths were associated with influenza A viruses. Two of the influenza A viruses had subtyping performed; one was an A(H1) virus, and one was an A(H3) virus.

                  A total of 138 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

                  View Full Screen

                  Additional pediatric mortality surveillance information for current and past seasons:
                  Surveillance Methods | FluView Interactive
                  Trend Indicators


                  Increasing:
                  Decreasing:
                  Stable:
                  Indicators Status by System


                  Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                  Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                  Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                  HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                  NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

                  Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                  Comment


                  • #24
                    Weekly U.S. Influenza Surveillance Report


                    Print
                    Updated April 7, 2023

                    Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                    Key Updates for Week 13, ending April 1, 2023

                    Seasonal influenza activity remains low nationally.
                    Viruses


                    Clinical Lab0.9%

                    (Trend )


                    positive for influenza
                    this week


                    Public Health Lab
                    The most frequently reported viruses this week were influenza A(H1N1).

                    Virus Characterization
                    Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
                    Illness


                    Outpatient Respiratory Illness2.3%

                    (Trend )


                    of visits to a health care provider this week were for respiratory illness
                    (below baseline).


                    Outpatient Respiratory Illness: Activity Map
                    This week 3 jurisdictions experienced moderate activity and 2 jurisdictions experienced high activity.

                    Long-term Care Facilities0.4%

                    (Trend )


                    of facilities reported
                    ≥ 1 influenza-positive test
                    among residents this week.


                    FluSurv-NET61.1 per 100,000


                    cumulative hospitalization rate

                    HHS Protect Hospitalizations1,230

                    (Trend )


                    patients admitted to hospitals with influenza
                    this week.


                    NCHS Mortality7.9%

                    (Trend )


                    of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                    Pediatric Deaths1


                    deaths were reported this week for a total of
                    139 so far this season


                    All data are preliminary and may change as more reports are received.

                    Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                    A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                    Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                    Key Points
                    • Seasonal influenza activity remains low nationally.
                    • Nationally, outpatient respiratory illness is below baseline, and eight of 10 HHS regions are below their respective baselines.
                    • The number and weekly rate of flu hospital admissions remain low.
                    • During week 13, 59.1% of viruses reported by public health laboratories were influenza A and 40.9% were influenza B. Of the 16 influenza A viruses detected and subtyped during week 13, 37.5% were influenza A(H3N2) and 62.5% were influenza A(H1N1).
                    • One influenza-associated pediatric death that occurred during the 2022-2023 season was reported this week, for a total of 139 pediatric flu deaths reported so far this season.
                    • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 18,000 deaths from flu.
                    • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                    • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                    • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                    • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
                    U.S. Virologic Surveillance


                    Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
                    Clinical Laboratories


                    The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

                    No. of specimens tested 51,569 2,929,567
                    No. of positive specimens (%) 482 (0.9%) 338,253 (11.5%)
                    Positive specimens by type
                    Influenza A 240 (49.8%) 333,382 (98.6%)
                    Influenza B 242 (50.2%) 4,871 (1.4%)


                    View Chart Data | View Full Screen
                    Public Health Laboratories


                    The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                    No. of specimens tested 4,415 219,677
                    No. of positive specimens 44 28,450
                    Positive specimens by type/subtype
                    Influenza A 26 (59.1%) 28,072 (98.8%)
                    (H1N1)pdm09 10 (62.5%) 6,184 (26.2%)
                    H3N2 6 (37.5%) 17,397 (73.8%)
                    H3N2v 0 1 (<0.1%)
                    Subtyping not performed 10 4,490
                    Influenza B 18 (40.9%) 378 (1.3%)
                    Yamagata lineage 0 0
                    Victoria lineage 8 (100%) 272 (100%)
                    Lineage not performed 10 106


                    View Chart Data | View Full Screen

                    Additional virologic surveillance information for current and past seasons:
                    Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
                    Influenza Virus Characterization


                    CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                    CDC genetically characterized 2,631 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2 but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2 and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                    A/H1 955
                    6B.1A.5a 955 (100%) 1 6 (0.6%)
                    2a 144 (15.1%)
                    2a.1 805 (84.3%)
                    A/H3 1,571
                    3C.2a1b.2a 1,571 (100%) 2a 25 (1.6%)
                    2a.1 182 (11.6%)
                    2a.1b 123 (7.8%)
                    2a.2c 0 (0%)
                    2a.3 46 (2.9%)
                    2a.3a 3 (0.2%)
                    2a.3a.1 55 (3.5%)
                    2a.3b 10 (0.6%)
                    2b 1,127 (71.7%)
                    B/Victoria 105
                    V1A 105 (100%) 3 4 (3.8%)
                    3a.2 101 (96.2%)
                    B/Yamagata 0
                    Y3 0 Y3 0 (0%)

                    CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                    Influenza A Viruses
                    • A (H1N1)pdm09: One hundred and eight A(H1N1)pdm09 viruses were antigenically characterized by HI, and 106 (98%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
                    • A (H3N2): One hundred and eighty A(H3N2) viruses were antigenically characterized by HINT, and 168 (93%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                    Influenza B Viruses
                    • B/Victoria: Sixteen influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                    • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                    Assessment of Virus Susceptibility to Antiviral Medications

                    CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                    Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                    Neuraminidase
                    Inhibitors
                    Oseltamivir Viruses
                    Tested
                    2,600 953 1,566 81 0
                    Reduced
                    Inhibition
                    1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                    Highly
                    Reduced
                    Inhibition
                    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                    Peramivir Viruses
                    Tested
                    2,600 953 1,566 81 0
                    Reduced
                    Inhibition
                    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                    Highly
                    Reduced
                    Inhibition
                    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                    Zanamivir Viruses
                    Tested
                    2,600 953 1,566 81 0
                    Reduced
                    Inhibition
                    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                    Highly
                    Reduced
                    Inhibition
                    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                    PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                    Tested
                    2,546 913 1,530 103 0
                    Reduced
                    Susceptibility
                    0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                    One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
                    Outpatient Respiratory Illness Surveillance


                    The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
                    Outpatient Respiratory Illness Visits


                    Nationwide during week 13, 2.3% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable compared to week 12 and is below the national baseline of 2.5%. Eight of the 10 HHS regions are below their respective baselines; regions 2 and 9 are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



                    * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                    View Chart Data (current season only) | View Full Screen
                    Outpatient Respiratory Illness Visits by Age Group


                    More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                    The percentage of visits for respiratory illness reported in ILINet remained stable (change of ≤ 0.1 percentage points) for all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, 65+ years) in week 13 compared to week 12.



                    View Chart Data | View Full Screen
                    Outpatient Respiratory Illness Activity Map


                    Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                    Week 13
                    (Week ending
                    Apr. 1, 2023)
                    Week 12
                    (Week ending
                    Mar. 25, 2023)
                    Week 13
                    (Week ending
                    Apr. 1, 2023)
                    Week 12
                    (Week ending
                    Mar. 25, 2023)
                    Very High 0 0 0 1
                    High 2 2 14 17
                    Moderate 3 3 24 30
                    Low 4 6 87 91
                    Minimal 45 43 554 544
                    Insufficient Data 1 1 250 246



                    *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                    Additional information about medically attended visits for ILI for current and past seasons:
                    Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
                    Long-term Care Facility (LTCF) Surveillance


                    LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 13, 60 (0.4%) of 14,394 reporting facilities reported at least one influenza positive test among their residents. This percentage remained stable compared to week 12.


                    View Chart Data | View Full Screen

                    Additional information about long-term care facility surveillance:
                    Surveillance Methods | Additional Data
                    Hospitalization Surveillance

                    FluSurv-NET


                    The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

                    A total of 17,865 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and April 1, 2023. The weekly hospitalization rate observed in week 13 was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

                    The overall cumulative hospitalization rate was 61.1 per 100,000 population. This in-season cumulative hospitalization rate is similar to the end-of-season hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the end-of-season hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                    When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (181.6). Among adults aged 65 and older, rates were highest among adults aged 85 and older (333.1). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (79.7) followed by adults aged 50-64 years (66). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (86.1), followed by non-Hispanic American Indian or Alaska Native persons (78.2), Hispanic/Latino (53.3), non-Hispanic White persons (52.0), and non-Hispanic Asian/Pacific Islander persons (26.8).

                    Among 17,865 hospitalizations, 17,178 (96.1%) were associated with influenza A virus, 518 (2.9%) with influenza B virus, 29 (0.2%) with influenza A virus and influenza B virus co-infection, and 140 (0.8%) with influenza virus for which the type was not determined. Among 4,442 hospitalizations with influenza A subtype information, 3,345 (75.3%) were A(H3N2), and 1,097 (24.7%) were A(H1N1)pdm09. Based on preliminary data, of the 5,127 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.8% (95% CI: 3.2%-4.5%) also tested positive for SARS-CoV-2.

                    Among 3,583 hospitalized adults with information on underlying medical conditions, 97.0% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 1,229 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 36.8% were pregnant. Among 1,280 hospitalized children with information on underlying medical conditions, 65.5% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease, and obesity.



                    View Full Screen



                    View Full Screen

                    Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                    Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
                    HHS Protect Hospitalization Surveillance


                    Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 13, 1,230 patients with laboratory-confirmed influenza were admitted to a hospital. The number of patients admitted to a hospital with laboratory-confirmed influenza remained stable compared to week 12.


                    View Chart Data | View Full Screen

                    Additional HHS Protect hospitalization surveillance information:
                    Surveillance Methods | Additional Data
                    Mortality Surveillance

                    National Center for Health Statistics (NCHS) Mortality Surveillance


                    Based on NCHS mortality surveillance data available on April 6, 2023, 7.9% of the deaths that occurred during the week ending April 1, 2023 (week 13), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remained stable (< 0.3 percentage point change) compared to week 12 and is above the epidemic threshold of 7.1% for this week. Among the 1,750 PIC deaths reported for this week, 572 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 19 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December, decreased for eight weeks, and has been stable at low levels for the past eight weeks. The data presented are preliminary and may change as more data are received and processed.

                    View Chart Data | View Full Screen

                    Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                    Surveillance Methods | FluView Interactive
                    Influenza-Associated Pediatric Mortality


                    One influenza-associated pediatric death occurring during the 2022-2023 season was reported to CDC during week 13. The death was associated with an influenza A(H3) virus and occurred during week 47 of 2022 (the week ending November 26, 2022).

                    A total of 139 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

                    View Full Screen

                    Additional pediatric mortality surveillance information for current and past seasons:
                    Surveillance Methods | FluView Interactive
                    Trend Indicators


                    Increasing:
                    Decreasing:
                    Stable:
                    Indicators Status by System


                    Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                    Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                    Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                    HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                    NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

                    Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                    Comment


                    • #25
                      Weekly U.S. Influenza Surveillance Report


                      Print
                      Updated April 14, 2023

                      Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                      Key Updates for Week 14, ending April 8, 2023

                      Seasonal influenza activity remains low nationally.
                      Viruses


                      Clinical Lab1.0%

                      (Trend )


                      positive for influenza
                      this week


                      Public Health Lab
                      Influenza A(H1N1) and influenza B viruses were the most frequently reported this week.

                      Virus Characterization
                      Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
                      Illness


                      Outpatient Respiratory Illness2.1%

                      (Trend )


                      of visits to a health care provider this week were for respiratory illness
                      (below baseline).


                      Outpatient Respiratory Illness: Activity Map
                      This week 3 jurisdictions experienced moderate activity and 2 jurisdictions experienced high activity.

                      Long-term Care Facilities0.3%

                      (Trend )


                      of facilities reported
                      ≥ 1 influenza-positive test
                      among residents this week.


                      FluSurv-NET61.4 per 100,000


                      cumulative hospitalization rate

                      HHS Protect Hospitalizations1,199

                      (Trend )


                      patients admitted to hospitals with influenza
                      this week.


                      NCHS Mortality7.6%

                      (Trend )


                      of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                      Pediatric Deaths2


                      deaths were reported this week for a total of
                      141 so far this season


                      All data are preliminary and may change as more reports are received.

                      Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                      A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                      Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                      Key Points
                      • Seasonal influenza activity remains low nationally.
                      • Nationally, outpatient respiratory illness is below baseline, and eight of 10 HHS regions are below their respective baselines.
                      • The number and weekly rate of flu hospital admissions remain low.
                      • During week 14, 57.1% of viruses reported by public health laboratories were influenza A and 42.9% were influenza B. Of the 24 influenza A viruses detected and subtyped during week 14, 29.2% were influenza A(H3N2) and 70.8% were influenza A(H1N1).
                      • Two influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 141 pediatric flu deaths reported so far this season.
                      • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 19,000 deaths from flu.
                      • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                      • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                      • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                      • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
                      U.S. Virologic Surveillance


                      Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
                      Clinical Laboratories


                      The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

                      No. of specimens tested 52,742 3,082,654
                      No. of positive specimens (%) 515 (1.0%) 349,474 (11.3%)
                      Positive specimens by type
                      Influenza A 269 (52.2%) 344,275 (98.5%)
                      Influenza B 246 (47.8%) 5,199 (1.5%)


                      View Chart Data | View Full Screen
                      Public Health Laboratories


                      The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                      No. of specimens tested 4,531 224,844
                      No. of positive specimens 56 28,607
                      Positive specimens by type/subtype
                      Influenza A 32 (57.1%) 28,178 (98.5%)
                      (H1N1)pdm09 17 (70.8%) 6,256 (26.4%)
                      H3N2 7 (29.2%) 17,422 (73.6%)
                      H3N2v 0 1 (<0.1%)
                      Subtyping not performed 8 4,499
                      Influenza B 24 (42.9%) 429 (1.5%)
                      Yamagata lineage 0 0
                      Victoria lineage 15 (100%) 322 (100%)
                      Lineage not performed 9 107


                      View Chart Data | View Full Screen

                      Additional virologic surveillance information for current and past seasons:
                      Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
                      Influenza Virus Characterization


                      CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                      CDC genetically characterized 2,688 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2 but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2 and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                      A/H1 972
                      6B.1A.5a 955 (100%) 1 6 (0.6%)
                      2a 146 (15.0%)
                      2a.1 820 (84.4%)
                      A/H3 1,595
                      3C.2a1b.2a 1,595 (100%) 2a 25 (1.6%)
                      2a.1 183 (11.5%)
                      2a.1b 129 (8.1%)
                      2a.2c 0 (0%)
                      2a.3 46 (2.9%)
                      2a.3a 3 (0.2%)
                      2a.3a.1 63 (3.9%)
                      2a.3b 10 (0.6%)
                      2b 1,136 (71.2%)
                      B/Victoria 121
                      V1A 105 (100%) 3 4 (3.3%)
                      3a.2 117 (96.2%)
                      B/Yamagata 0
                      Y3 0 Y3 0 (0%)

                      CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                      Influenza A Viruses
                      • A (H1N1)pdm09: One hundred and eight A(H1N1)pdm09 viruses were antigenically characterized by HI, and 106 (98%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
                      • A (H3N2): One hundred and eighty-nine A(H3N2) viruses were antigenically characterized by HINT, and 177 (94%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                      Influenza B Viruses
                      • B/Victoria: Sixteen influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                      • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                      Assessment of Virus Susceptibility to Antiviral Medications

                      CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                      Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                      Neuraminidase
                      Inhibitors
                      Oseltamivir Viruses
                      Tested
                      2,642 971 1,590 81 0
                      Reduced
                      Inhibition
                      1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                      Highly
                      Reduced
                      Inhibition
                      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                      Peramivir Viruses
                      Tested
                      2,642 971 1,590 81 0
                      Reduced
                      Inhibition
                      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                      Highly
                      Reduced
                      Inhibition
                      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                      Zanamivir Viruses
                      Tested
                      2,642 971 1,590 81 0
                      Reduced
                      Inhibition
                      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                      Highly
                      Reduced
                      Inhibition
                      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                      PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                      Tested
                      2,602 930 1,554 118 0
                      Reduced
                      Susceptibility
                      0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                      One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
                      Outpatient Respiratory Illness Surveillance


                      The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
                      Outpatient Respiratory Illness Visits


                      Nationwide during week 14, 2.1% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has decreased compared to week 13 and is below the national baseline of 2.5%. Eight of 10 HHS regions are below their respective baselines; regions 2 and 9 are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



                      * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                      View Chart Data (current season only) | View Full Screen
                      Outpatient Respiratory Illness Visits by Age Group


                      More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                      The percentage of visits for respiratory illness reported in ILINet decreased for one age group (5-24 years) and remained stable (change of ≤ 0.1 percentage points) for the remaining four age groups (0-4 years, 25-49 years, 50-64 years, and 65+ years) in week 14 compared to week 13.



                      View Chart Data | View Full Screen
                      Outpatient Respiratory Illness Activity Map


                      Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                      Week 14
                      (Week ending
                      Apr. 8, 2023)
                      Week 13
                      (Week ending
                      Apr. 1, 2023)
                      Week 14
                      (Week ending
                      Apr. 8, 2023)
                      Week 13
                      (Week ending
                      Apr. 1, 2023)
                      Very High 0 0 1 1
                      High 2 2 14 17
                      Moderate 3 3 24 29
                      Low 4 6 89 92
                      Minimal 45 43 555 545
                      Insufficient Data 1 1 246 245



                      *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                      Additional information about medically attended visits for ILI for current and past seasons:
                      Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
                      Long-term Care Facility (LTCF) Surveillance


                      LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 14, 42 (0.3%) of 14,323 reporting facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 13.


                      View Chart Data | View Full Screen

                      Additional information about long-term care facility surveillance:
                      Surveillance Methods | Additional Data
                      Hospitalization Surveillance

                      FluSurv-NET


                      The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

                      A total of 17,969 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and April 8, 2023. The weekly hospitalization rate observed in week 14 was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

                      The overall cumulative hospitalization rate was 61.4 per 100,000 population. This in-season cumulative hospitalization rate is similar to the end-of-season hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the end-of-season hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                      When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (182.7). Among adults aged 65 and older, rates were highest among adults aged 85 and older (335.6). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (79.9) followed by adults aged 50-64 years (66.4). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (86.6), followed by non-Hispanic American Indian or Alaska Native persons (80.2), Hispanic/Latino persons (53.6), non-Hispanic White persons (52.3), and non-Hispanic Asian/Pacific Islander persons (26.9).

                      Among 17,969 hospitalizations, 17,251 (96%) were associated with influenza A virus, 545 (3%) with influenza B virus, 30 (0.2%) with influenza A virus and influenza B virus co-infection, and 143 (0.8%) with influenza virus for which the type was not determined. Among 4,451 hospitalizations with influenza A subtype information, 3,347 (75.2%) were A(H3N2), and 1,104 (24.8%) were A(H1N1)pdm09. Based on preliminary data, of the 5,206 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.8% (95% CI: 3.2%-4.5%) also tested positive for SARS-CoV-2.

                      Among 3,655 hospitalized adults with information on underlying medical conditions, 97.0% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 1,270 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 37.1% were pregnant. Among 1,297 hospitalized children with information on underlying medical conditions, 65.6% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease and obesity.



                      View Full Screen



                      View Full Screen

                      Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                      Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
                      HHS Protect Hospitalization Surveillance


                      Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 14, 1,199 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 13.


                      View Chart Data | View Full Screen

                      Additional HHS Protect hospitalization surveillance information:
                      Surveillance Methods | Additional Data
                      Mortality Surveillance

                      National Center for Health Statistics (NCHS) Mortality Surveillance


                      Based on NCHS mortality surveillance data available on April 13, 2023, 7.6% of the deaths that occurred during the week ending April 8, 2023 (week 14), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remained stable (< 0.3 percentage point change) compared to week 13 and is above the epidemic threshold of 7.0% for this week. Among the 1,611 PIC deaths reported for this week, 509 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 13 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December, decreased for eight weeks, and has been stable at low levels for the past nine weeks. The data presented are preliminary and may change as more data are received and processed.

                      View Chart Data | View Full Screen

                      Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                      Surveillance Methods | FluView Interactive
                      Influenza-Associated Pediatric Mortality


                      Two influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 14. One death was associated with an influenza A(H3) virus and occurred during week 51 of 2022 (the week ending December 24, 2022). The other death was associated with an influenza A virus for which no subtyping was performed and occurred during week 11 of 2023 (the week ending March 18, 2023).

                      A total of 141 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

                      View Full Screen

                      Additional pediatric mortality surveillance information for current and past seasons:
                      Surveillance Methods | FluView Interactive
                      Trend Indicators


                      Increasing:
                      Decreasing:
                      Stable:
                      Indicators Status by System


                      Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                      Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                      Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                      HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                      NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

                      Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                      Comment


                      • #26
                        Weekly U.S. Influenza Surveillance Report


                        Print
                        Updated April 21, 2023

                        Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                        Key Updates for Week 15, ending April 15, 2023

                        Seasonal influenza activity remains low nationally.
                        Viruses


                        Clinical Lab1.0%

                        (Trend )


                        positive for influenza
                        this week


                        Public Health Lab
                        Influenza A(H1N1) and influenza B viruses were the most frequently reported this week.

                        Virus Characterization
                        Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
                        Illness


                        Outpatient Respiratory Illness2.0%

                        (Trend )


                        of visits to a health care provider this week were for respiratory illness
                        (below baseline).


                        Outpatient Respiratory Illness: Activity Map
                        This week 4 jurisdictions experienced moderate activity and no jurisdictions experienced high or very high activity.

                        Long-term Care Facilities0.4%

                        (Trend )


                        of facilities reported
                        ≥ 1 influenza-positive test
                        among residents this week.


                        FluSurv-NET61.5 per 100,000


                        cumulative hospitalization rate

                        HHS Protect Hospitalizations1,072

                        (Trend )


                        patients admitted to hospitals with influenza
                        this week.


                        NCHS Mortality7.5%

                        (Trend )


                        of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                        Pediatric Deaths2


                        deaths were reported this week for a total of
                        143 so far this season


                        All data are preliminary and may change as more reports are received.

                        Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                        A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                        Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                        Key Points
                        • Seasonal influenza activity remains low nationally.
                        • Nationally, outpatient respiratory illness is below baseline, and nine of 10 HHS regions are below their respective baselines.
                        • The number and weekly rate of flu hospital admissions remain low.
                        • During week 15, 59.5% of viruses reported by public health laboratories were influenza A and 40.5% were influenza B. Of the 13 influenza A viruses detected and subtyped during week 15, one was influenza A(H3N2) and 12 were influenza A(H1N1).
                        • Two influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 143 pediatric flu deaths reported so far this season.
                        • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 19,000 deaths from flu.
                        • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                        • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                        • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                        • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
                        U.S. Virologic Surveillance


                        Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses.
                        Clinical Laboratories


                        The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

                        No. of specimens tested 44,819 3,143,784
                        No. of positive specimens (%) 453 (1.0%) 350,104 (11.1%)
                        Positive specimens by type
                        Influenza A 203 (44.8%) 344,586 (98.4%)
                        Influenza B 250 (55.2%) 5,518 (1.6%)


                        View Chart Data | View Full Screen
                        Public Health Laboratories


                        The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                        No. of specimens tested 4,416 229,669
                        No. of positive specimens 37 28,759
                        Positive specimens by type/subtype
                        Influenza A 22 (59.5%) 28,282 (98.3%)
                        (H1N1)pdm09 12 (92.3%) 6,335 (26.6%)
                        H3N2 1 (7.7%) 17,437 (73.3%)
                        H3N2v 0 1 (<0.1%)
                        Subtyping not performed 9 4,509
                        Influenza B 15 (40.5%) 477 (1.7%)
                        Yamagata lineage 0 0
                        Victoria lineage 11 (100%) 362 (100%)
                        Lineage not performed 4 115


                        View Chart Data | View Full Screen

                        Additional virologic surveillance information for current and past seasons:
                        Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
                        Influenza Virus Characterization


                        CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                        CDC genetically characterized 2,691 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2 but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2 and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                        A/H1 973
                        6B.1A.5a 973 (100%) 1 6 (0.6%)
                        2a 147 (15.0%)
                        2a.1 820 (84.4%)
                        A/H3 1,597
                        3C.2a1b.2a 1,597 (100%) 2a 25 (1.6%)
                        2a.1 183 (11.5%)
                        2a.1b 129 (8.1%)
                        2a.2c 0 (0%)
                        2a.3 46 (2.9%)
                        2a.3a 3 (0.2%)
                        2a.3a.1 63 (3.9%)
                        2a.3b 10 (0.6%)
                        2b 1,138 (71.3%)
                        B/Victoria 121
                        V1A 121 (100%) 3 4 (3.3%)
                        3a.2 117 (96.7%)
                        B/Yamagata 0
                        Y3 0 Y3 0 (0%)

                        CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                        Influenza A Viruses
                        • A (H1N1)pdm09: One hundred and twenty-three A(H1N1)pdm09 viruses were antigenically characterized by HI, and 119 (97%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
                        • A (H3N2): One hundred and eighty-nine A(H3N2) viruses were antigenically characterized by HINT, and 177 (94%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                        Influenza B Viruses
                        • B/Victoria: Sixteen influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                        • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                        Assessment of Virus Susceptibility to Antiviral Medications

                        CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                        Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                        Neuraminidase
                        Inhibitors
                        Oseltamivir Viruses
                        Tested
                        2,691 976 1,595 120 0
                        Reduced
                        Inhibition
                        1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                        Highly
                        Reduced
                        Inhibition
                        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                        Peramivir Viruses
                        Tested
                        2,691 976 1,595 120 0
                        Reduced
                        Inhibition
                        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                        Highly
                        Reduced
                        Inhibition
                        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                        Zanamivir Viruses
                        Tested
                        2,691 976 1,595 120 0
                        Reduced
                        Inhibition
                        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                        Highly
                        Reduced
                        Inhibition
                        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                        PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                        Tested
                        2,610 936 1,556 118 0
                        Reduced
                        Susceptibility
                        0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                        One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir.
                        Outpatient Respiratory Illness Surveillance


                        The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
                        Outpatient Respiratory Illness Visits


                        Nationwide during week 15, 2.0% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has decreased compared to week 14 and is below the national baseline of 2.5%. Nine of 10 HHS regions are below their respective baselines; Region 9 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.



                        * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                        View Chart Data (current season only) | View Full Screen
                        Outpatient Respiratory Illness Visits by Age Group


                        More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                        The percentage of visits for respiratory illness reported in ILINet decreased for two age groups (0-4 years and 5-24 years) and remained stable (change of ≤ 0.1 percentage points) for the remaining three age groups (25-49 years, 50-64 years, and 65+ years) in week 15 compared to week 14.



                        View Chart Data | View Full Screen
                        Outpatient Respiratory Illness Activity Map


                        Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                        Week 15
                        (Week ending
                        Apr. 15, 2023)
                        Week 14
                        (Week ending
                        Apr. 8, 2023)
                        Week 15
                        (Week ending
                        Apr. 15, 2023)
                        Week 14
                        (Week ending
                        Apr. 8, 2023)
                        Very High 0 0 0 1
                        High 0 2 7 15
                        Moderate 4 3 23 21
                        Low 2 3 56 69
                        Minimal 48 46 586 572
                        Insufficient Data 1 1 257 251



                        *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                        Additional information about medically attended visits for ILI for current and past seasons:
                        Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
                        Long-term Care Facility (LTCF) Surveillance


                        LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 15, 55 (0.4%) of 14,356 reporting facilities reported at least one influenza positive test among their residents. This increased by > 5% compared to week 14.


                        View Chart Data | View Full Screen

                        Additional information about long-term care facility surveillance:
                        Surveillance Methods | Additional Data
                        Hospitalization Surveillance

                        FluSurv-NET


                        A total of 17,997 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and April 15, 2023. The weekly hospitalization rate observed in week 15 was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

                        The overall cumulative hospitalization rate was 61.5 per 100,000 population. This in-season cumulative hospitalization rate is similar to the end-of-season hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the end-of-season hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                        When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (183.4). Among adults aged 65 and older, rates were highest among adults aged 85 and older (336). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (79.5) followed by adults aged 50-64 years (66.8). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (86.8), followed by non-Hispanic American Indian or Alaska Native persons (80.2), Hispanic/Latino persons (53.9), non-Hispanic White persons (52.6), and non-Hispanic Asian/Pacific Islander persons (26.9).

                        Among 17,997 hospitalizations, 17,255 (95.9%) were associated with influenza A virus, 571 (3.2%) with influenza B virus, 30 (0.2%) with influenza A virus and influenza B virus co-infection, and 141 (0.8%) with influenza virus for which the type was not determined. Among 4,483 hospitalizations with influenza A subtype information, 3,362 (75%) were A(H3N2), and 1,121 (25.0%) were A(H1N1)pdm09. Based on preliminary data, of the 5,278 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.8% (95% CI: 3.1%-4.5%) also tested positive for SARS-CoV-2.

                        Among 3,702 hospitalized adults with information on underlying medical conditions, 97.0% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 1,302 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 37.3% were pregnant. Among 1,275 hospitalized children with information on underlying medical conditions, 66.2% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease and obesity.



                        View Full Screen



                        View Full Screen

                        Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                        Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive
                        HHS Protect Hospitalization Surveillance


                        Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 15, 1,072 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 14.


                        View Chart Data | View Full Screen

                        Additional HHS Protect hospitalization surveillance information:
                        Surveillance Methods | Additional Data
                        Mortality Surveillance

                        National Center for Health Statistics (NCHS) Mortality Surveillance


                        Based on NCHS mortality surveillance data available on April 20, 2023, 7.5% of the deaths that occurred during the week ending April 15, 2023 (week 15), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remained stable (< 0.3 percentage point change) compared to week 14 and is above the epidemic threshold of 6.9% for this week. Among the 1,732 PIC deaths reported for this week, 523 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 18 listed influenza. The data presented are preliminary and may change as more data are received and processed.

                        View Chart Data | View Full Screen

                        Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                        Surveillance Methods | FluView Interactive
                        Influenza-Associated Pediatric Mortality


                        Two influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 15. One death was associated with an influenza A virus for which no subtyping was performed and occurred during week 50 of 2022 (the week ending December 17, 2022). The other death was associated with an influenza A(H1N1) virus and occurred during week 1 of 2023 (the week ending January 7, 2023).

                        A total of 143 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

                        View Full Screen

                        Additional pediatric mortality surveillance information for current and past seasons:
                        Surveillance Methods | FluView Interactive
                        Trend Indicators


                        Increasing:
                        Decreasing:
                        Stable:
                        Indicators Status by System


                        Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                        Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                        Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                        HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                        NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

                        Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                        Comment


                        • #27
                          Weekly U.S. Influenza Surveillance Report


                          Print
                          Updated April 28, 2023

                          Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                          Key Updates for Week 16, ending April 22, 2023

                          Seasonal influenza activity remains low nationally. Viruses


                          Clinical Lab 0.8%

                          (Trend )


                          positive for influenza
                          this week


                          Public Health Lab
                          Influenza A(H1N1) and influenza B viruses were the most frequently reported this week.

                          Virus Characterization
                          Genetic and antigenic characterization and antiviral susceptibility are summarized in this report. Illness


                          Outpatient Respiratory Illness 1.9%

                          (Trend )


                          of visits to a health care provider this week were for respiratory illness
                          (below baseline).


                          Outpatient Respiratory Illness: Activity Map
                          This week 1 jurisdiction experienced moderate activity and 1jurisdiction experienced high or very high activity.

                          Long-term Care Facilities 0.3%

                          (Trend )


                          of facilities reported
                          ≥ 1 influenza-positive test
                          among residents this week.


                          FluSurv-NET 61.8 per 100,000


                          cumulative hospitalization rate

                          HHS Protect Hospitalizations 984

                          (Trend )


                          patients admitted to hospitals with influenza
                          this week.


                          NCHS Mortality 7.5%

                          (Trend )


                          of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                          Pediatric Deaths 2


                          deaths were reported this week for a total of
                          145 so far this season


                          All data are preliminary and may change as more reports are received.

                          Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                          A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                          Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                          Key Points
                          • Seasonal influenza activity remains low nationally.
                          • Nationally, outpatient respiratory illness is below baseline, and nine of 10 HHS regions are below their respective baselines.
                          • The number and weekly rate of flu hospital admissions remain low.
                          • During week 16, 60.5% of viruses reported by public health laboratories were influenza A and 39.5% were influenza B. Of the 17 influenza A viruses detected and subtyped during week 16, 4 were influenza A(H3N2) and 13 were influenza A(H1N1).
                          • Two influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 145 pediatric flu deaths reported so far this season.
                          • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 19,000 deaths from flu.
                          • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                          • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                          • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                          • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
                          U.S. Virologic Surveillance


                          Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses. Clinical Laboratories


                          The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
                          No. of specimens tested 35,045 3,192,508
                          No. of positive specimens (%) 283 (0.8%) 350,513 (11.0%)
                          Positive specimens by type
                          Influenza A 124 (43.8%) 344,757 (98.4%)
                          Influenza B 159 (56.2%) 5,756 (1.6%)
                          INFLUENZA Virus Isolated

                          View Chart Data | View Full Screen Public Health Laboratories


                          The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                          No. of specimens tested 3,542 233,873
                          No. of positive specimens 38 28,897
                          Positive specimens by type/subtype
                          Influenza A 23 (60.5%) 28,369 (98.2%)
                          (H1N1)pdm09 13 (76.5%) 6,395 (26.8%)
                          H3N2 4 (23.5%) 17,458 (73.2%)
                          H3N2v 0 1 (<0.1%)
                          Subtyping not performed 6 4,515
                          Influenza B 15 (39.5%) 527 (1.8%)
                          Yamagata lineage 0 0
                          Victoria lineage 9 (100%) 395 (100%)
                          Lineage not performed 6 132

                          INFLUENZA Virus Isolated
                          View Chart Data | View Full Screen

                          Additional virologic surveillance information for current and past seasons:
                          Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data Influenza Virus Characterization


                          CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                          CDC genetically characterized 2,761 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2, but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2, and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                          A/H1 1,011
                          6B.1A.5a 1,011 (100%) 1 6 (0.6%)
                          2a 152 (15.1%)
                          2a.1 853 (84.3%)
                          A/H3 1,618
                          3C.2a1b.2a 1,618 (100%) 2a 25 (1.5%)
                          2a.1 184 (11.4%)
                          2a.1b 132 (8.2%)
                          2a.2c 0 (0%)
                          2a.3 46 (2.8%)
                          2a.3a 3 (0.2%)
                          2a.3a.1 67 (4.1%)
                          2a.3b 10 (0.6%)
                          2b 1,151 (71.1%)
                          B/Victoria 132
                          V1A 132 (100%) 3 4 (3.0%)
                          3a.2 123 (97.0%)
                          B/Yamagata 0
                          Y3 0 Y3 0 (0%)

                          CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                          Influenza A Viruses
                          • A (H1N1)pdm09: One hundred and thirty-two A(H1N1)pdm09 viruses were antigenically characterized by HI, and 128 (97%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
                          • A (H3N2): One hundred and eighty-nine A(H3N2) viruses were antigenically characterized by HINT, and 177 (94%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                          Influenza B Viruses
                          • B/Victoria: Twenty-eight influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                          • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                          Assessment of Virus Susceptibility to Antiviral Medications

                          CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                          Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                          Neuraminidase
                          Inhibitors
                          Oseltamivir Viruses
                          Tested
                          2,774 1,017 1,622 135 0
                          Reduced
                          Inhibition
                          1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                          Highly
                          Reduced
                          Inhibition
                          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                          Peramivir Viruses
                          Tested
                          2,774 1,017 1,622 135 0
                          Reduced
                          Inhibition
                          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                          Highly
                          Reduced
                          Inhibition
                          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                          Zanamivir Viruses
                          Tested
                          2,774 1,017 1,622 135 0
                          Reduced
                          Inhibition
                          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                          Highly
                          Reduced
                          Inhibition
                          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                          PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                          Tested
                          2,690 974 1,583 133 0
                          Reduced
                          Susceptibility
                          0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                          One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir. Outpatient Respiratory Illness Surveillance


                          The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website. Outpatient Respiratory Illness Visits


                          Nationwide during week 16, 1.9% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable compared to week 15 and is below the national baseline of 2.5%. Nine of 10 HHS regions are below their respective baselines; Region 9 is above baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.

                          national levels of ILI and ARI

                          * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                          View Chart Data (current season only) | View Full Screen Outpatient Respiratory Illness Visits by Age Group


                          More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                          The percentage of visits for respiratory illness reported in ILINet decreased for one age group (0-4 years) and remained stable (change of ≤ 0.1 percentage points) for four age groups (5-24 years, 25-49 years, 50-64 years, and 65+ years) in week 16 compared to week 15.

                          national levels of ILI and ARI by age group

                          View Chart Data | View Full Screen Outpatient Respiratory Illness Activity Map


                          Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                          Week 16
                          (Week ending
                          Apr. 22, 2023)
                          Week 15
                          (Week ending
                          Apr. 15, 2023)
                          Week 16
                          (Week ending
                          Apr. 22, 2023)
                          Week 15
                          (Week ending
                          Apr. 15, 2023)
                          Very High 0 0 0 1
                          High 1 0 8 10
                          Moderate 1 3 13 23
                          Low 3 4 63 58
                          Minimal 50 48 597 598
                          Insufficient Data 0 0 248 239



                          *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                          Additional information about medically attended visits for ILI for current and past seasons:
                          Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map Long-term Care Facility (LTCF) Surveillance


                          LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 16, 37 (0.3%) of 14,315 reporting facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 15.

                          national levels of ltcf influenza
                          View Chart Data | View Full Screen

                          Additional information about long-term care facility surveillance:
                          Surveillance Methods | Additional Data Hospitalization Surveillance

                          FluSurv-NET


                          The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 13 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

                          A total of 18,070 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and April 22, 2023. The weekly hospitalization rate observed in week 16 was 0.1 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

                          The overall cumulative hospitalization rate was 61.8 per 100,000 population. This in-season cumulative hospitalization rate is similar to the end-of-season hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the end-of-season hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                          When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (184.1). Among adults aged 65 and older, rates were highest among adults aged 85 and older (337.2). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (80.0) followed by adults aged 50-64 years (66.9). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (87.2), followed by non-Hispanic American Indian or Alaska Native persons (82.2), Hispanic/Latino persons (54.2), non-Hispanic White persons (52.8), and non-Hispanic Asian/Pacific Islander persons (27.1).

                          Among 18,070 hospitalizations, 17,291 (95.7%) were associated with influenza A virus, 604 (3.3%) with influenza B virus, 29 (0.2%) with influenza A virus and influenza B virus co-infection, and 146 (0.8%) with influenza virus for which the type was not determined. Among 4,497 hospitalizations with influenza A subtype information, 3,372 (75%) were A(H3N2), and 1,125 (25.0%) were A(H1N1)pdm09. Based on preliminary data, of the 5,340 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.8% (95% CI: 3.2%-4.5%) also tested positive for SARS-CoV-2.

                          Among 3,732 hospitalized adults with information on underlying medical conditions, 97.1% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 1,346 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 37.2% were pregnant. Among 1,288 hospitalized children with information on underlying medical conditions, 66.1% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease, and obesity.

                          FluSurvNet Cumulative Rates

                          View Full Screen

                          FluSurvNet Characteristics

                          View Full Screen

                          Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                          Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive HHS Protect Hospitalization Surveillance


                          Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 16, 984 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 15.

                          national levels of influenza hospitalizations
                          View Chart Data | View Full Screen

                          Additional HHS Protect hospitalization surveillance information:
                          Surveillance Methods | Additional Data Mortality Surveillance

                          National Center for Health Statistics (NCHS) Mortality Surveillance


                          Based on NCHS mortality surveillance data available on April 27, 2023, 7.5% of the deaths that occurred during the week ending April 22, 2023 (week 16), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remained stable (< 0.3 percentage point change) compared to week 15 and is above the epidemic threshold of 6.8% for this week. Among the 1,705 PIC deaths reported for this week, 470 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 12 listed influenza. The data presented are preliminary and may change as more data are received and processed.

                          Click on image to launch interactive toolView Chart Data | View Full Screen

                          Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                          Surveillance Methods | FluView Interactive Influenza-Associated Pediatric Mortality


                          Two influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 16. One death was associated with an influenza A virus for which no subtyping was performed and occurred during week 1 (the week ending January 7, 2023). The other death was associated with an influenza B virus with no lineage determined and occurred during week 15 (the week ending April 15, 2023).

                          A total of 145 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

                          Click on image to launch interactive tool View Full Screen

                          Additional pediatric mortality surveillance information for current and past seasons:
                          Surveillance Methods | FluView Interactive Trend Indicators


                          Increasing:
                          Decreasing:
                          Stable: Indicators Status by System


                          Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                          Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                          Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                          HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                          NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

                          Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                          Comment


                          • #28
                            Weekly U.S. Influenza Surveillance Report


                            Print
                            Updated May 5, 2023

                            Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                            Key Updates for Week 17, ending April 29, 2023

                            Seasonal influenza activity remains low nationally. Viruses


                            Clinical Lab 1.0%

                            (Trend )


                            positive for influenza
                            this week


                            Public Health Lab
                            Influenza B viruses were the most frequently reported this week.

                            Virus Characterization
                            Genetic and antigenic characterization and antiviral susceptibility are summarized in this report. Illness


                            Outpatient Respiratory Illness 2.0%

                            (Trend )


                            of visits to a health care provider this week were for respiratory illness
                            (below baseline).


                            Outpatient Respiratory Illness: Activity Map
                            This week 2 jurisdictions experienced moderate activity and 1 jurisdiction experienced high or very high activity.

                            Long-term Care Facilities 0.4%

                            (Trend )


                            of facilities reported
                            ≥ 1 influenza-positive test
                            among residents this week.


                            FluSurv-NET 61.9 per 100,000


                            cumulative hospitalization rate

                            HHS Protect Hospitalizations 911

                            (Trend )


                            patients admitted to hospitals with influenza
                            this week.


                            NCHS Mortality 7.3%

                            (Trend )


                            of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                            Pediatric Deaths 5


                            deaths were reported (1 occurred in 2021-22 season and 4 occurred in 2022-23 season).

                            All data are preliminary and may change as more reports are received.

                            Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                            A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                            Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                            Key Points
                            • Seasonal influenza activity remains low nationally.
                            • Nationally, outpatient respiratory illness is below baseline, and nine of 10 HHS regions are below their respective baselines.
                            • The number and weekly rate of flu hospital admissions remain low.
                            • During week 17, 36.0% of viruses reported by public health laboratories were influenza A and 64.0% were influenza B. Of the 12 influenza A viruses detected and subtyped during week 17, 3 were influenza A(H3N2) and 9 were influenza A(H1N1).
                            • Four influenza-associated pediatric deaths that occurred during the 2022-2023 season were reported this week, for a total of 149 pediatric flu deaths reported so far this season.
                            • CDC estimates that, so far this season, there have been at least 26 million illnesses, 290,000 hospitalizations, and 19,000 deaths from flu.
                            • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                            • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                            • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                            • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
                            U.S. Virologic Surveillance


                            Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses. Clinical Laboratories


                            The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
                            No. of specimens tested 35,837 3,250,101
                            No. of positive specimens (%) 371 (1.0%) 351,174 (10.8%)
                            Positive specimens by type
                            Influenza A 156 (42.0%) 345,008 (98.2%)
                            Influenza B 215 (58.0%) 6,166 (1.8%)
                            INFLUENZA Virus Isolated

                            View Chart Data | View Full Screen Public Health Laboratories


                            The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                            No. of specimens tested 3,661 238,025
                            No. of positive specimens 50 29,012
                            Positive specimens by type/subtype
                            Influenza A 18 (36.0%) 28,416 (97.9%)
                            (H1N1)pdm09 9 (75.0%) 6,420 (26.9%)
                            H3N2 3 (25.0%) 17,463 (73.1%)
                            H3N2v 0 1 (<0.1%)
                            Subtyping not performed 6 4,532
                            Influenza B 32 (64.0%) 596 (2.1%)
                            Yamagata lineage 0 0
                            Victoria lineage 22 (100%) 444 (100%)
                            Lineage not performed 10 152

                            INFLUENZA Virus Isolated
                            View Chart Data | View Full Screen

                            Additional virologic surveillance information for current and past seasons:
                            Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data Influenza Virus Characterization


                            CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                            CDC genetically characterized 2,813 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2, but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2, and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                            A/H1 1,029
                            6B.1A.5a 1,029 (100%) 1 6 (0.6%)
                            2a 156 (15.2%)
                            2a.1 867 (84.3%)
                            A/H3 1,627
                            3C.2a1b.2a 1,627 (100%) 2a 25 (1.5%)
                            2a.1 184 (11.3%)
                            2a.1b 133 (8.2%)
                            2a.3 46 (2.8%)
                            2a.3a 3 (0.2%)
                            2a.3a.1 70 (4.3%)
                            2a.3b 11 (0.7%)
                            2b 1,155 (71.0%)
                            2c 0 (0%)
                            B/Victoria 157
                            V1A 157 (100%) 3 4 (2.5%)
                            3a.2 153 (97.5%)
                            B/Yamagata 0
                            Y3 0 Y3 0 (0%)

                            CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                            Influenza A Viruses
                            • A (H1N1)pdm09: One hundred and sixty-two A(H1N1)pdm09 viruses were antigenically characterized by HI, and 158 (98%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant- based influenza vaccines.
                            • A (H3N2): Two hundred and three A(H3N2) viruses were antigenically characterized by HINT, and 191 (94%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                            Influenza B Viruses
                            • B/Victoria: Forty-five influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                            • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                            Assessment of Virus Susceptibility to Antiviral Medications

                            CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                            Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                            Neuraminidase
                            Inhibitors
                            Oseltamivir Viruses
                            Tested
                            2,801 1,023 1,622 156 0
                            Reduced
                            Inhibition
                            1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                            Highly
                            Reduced
                            Inhibition
                            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                            Peramivir Viruses
                            Tested
                            2,801 1,023 1,622 156 0
                            Reduced
                            Inhibition
                            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                            Highly
                            Reduced
                            Inhibition
                            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                            Zanamivir Viruses
                            Tested
                            2,801 1,023 1,622 156 0
                            Reduced
                            Inhibition
                            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                            Highly
                            Reduced
                            Inhibition
                            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                            PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                            Tested
                            2,716 979 1,583 154 0
                            Reduced
                            Susceptibility
                            0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                            One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir. Outpatient Respiratory Illness Surveillance


                            The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website. Outpatient Respiratory Illness Visits


                            Nationwide during week 17, 2.0% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable (change of ≤ 0.1 percentage points) compared to week 16 and is below the national baseline of 2.5%. Nine of 10 HHS regions are below their respective baselines; Region 9 is at baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.

                            national levels of ILI and ARI

                            * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                            View Chart Data (current season only) | View Full Screen Outpatient Respiratory Illness Visits by Age Group


                            More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                            The percentage of visits for respiratory illness reported in ILINet remained stable (change of ≤ 0.1 percentage points) for all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years) in week 17 compared to week 16.

                            national levels of ILI and ARI by age group

                            View Chart Data | View Full Screen Outpatient Respiratory Illness Activity Map


                            Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                            Week 17
                            (Week ending
                            Apr. 29, 2023)
                            Week 16
                            (Week ending
                            Apr. 22, 2023)
                            Week 17
                            (Week ending
                            Apr. 29, 2023)
                            Week 16
                            (Week ending
                            Apr. 22, 2023)
                            Very High 0 0 0 0
                            High 1 1 6 9
                            Moderate 2 1 15 14
                            Low 3 4 49 62
                            Minimal 49 49 610 606
                            Insufficient Data 0 0 249 238



                            *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                            Additional information about medically attended visits for ILI for current and past seasons:
                            Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map Long-term Care Facility (LTCF) Surveillance


                            LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 17, 52 (0.4%) of 14,343 reporting facilities reported at least one influenza positive test among their residents. This increased by > 5% compared to week 16.

                            national levels of ltcf influenza
                            View Chart Data | View Full Screen

                            Additional information about long-term care facility surveillance:
                            Surveillance Methods | Additional Data Hospitalization Surveillance

                            FluSurv-NET


                            The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 13 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

                            A total of 18,105 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and April 29, 2023. The weekly hospitalization rate observed in week 17 was 0.1 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

                            The overall cumulative hospitalization rate was 61.9 per 100,000 population. This in-season cumulative hospitalization rate is similar to the end-of-season hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the end-of-season hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                            When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (184.3). Among adults aged 65 and older, rates were highest among adults aged 85 and older (337.7). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (80.3), followed by adults aged 50-64 years (67.1). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (87.5), followed by non-Hispanic American Indian or Alaska Native persons (81.2), Hispanic/Latino persons (54.5), non-Hispanic White persons (53.0), and non-Hispanic Asian/Pacific Islander persons (27.2).

                            Among 18,105 hospitalizations, 17,315 (95.6%) were associated with influenza A virus, 617 (3.4%) with influenza B virus, 30 (0.2%) with influenza A virus and influenza B virus co-infection, and 143 (0.8%) with influenza virus for which the type was not determined. Among 4,524 hospitalizations with influenza A subtype information, 3,388 (74.9%) were A(H3N2), and 1,136 (25.1%) were A(H1N1)pdm09. Based on preliminary data, of the 5,393 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.8% (95% CI: 3.1%-4.5%) also tested positive for SARS-CoV-2.

                            Among 3,761 hospitalized adults with information on underlying medical conditions, 97.1% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 1,394 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 37.1% were pregnant. Among 1,298 hospitalized children with information on underlying medical conditions, 66.0% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease, and obesity.

                            FluSurvNet Cumulative Rates

                            View Full Screen

                            FluSurvNet Characteristics

                            View Full Screen

                            Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                            Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive HHS Protect Hospitalization Surveillance


                            Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 17, 911 patients with laboratory-confirmed influenza were admitted to a hospital. The number of patients admitted to a hospital with laboratory-confirmed influenza remained stable compared to week 16.

                            national levels of influenza hospitalizations
                            View Chart Data | View Full Screen

                            Additional HHS Protect hospitalization surveillance information:
                            Surveillance Methods | Additional Data Mortality Surveillance

                            National Center for Health Statistics (NCHS) Mortality Surveillance


                            Based on NCHS mortality surveillance data available on May 4, 2023, 7.3% of the deaths that occurred during the week ending April 29, 2023 (week 17), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage decreased (> 0.3 percentage point change) compared to week 16 and is above the epidemic threshold of 6.8% for this week. Among the 1,585 PIC deaths reported for this week, 439 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 14 listed influenza. The data presented are preliminary and may change as more data are received and processed.

                            Click on image to launch interactive toolView Chart Data | View Full Screen

                            Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                            Surveillance Methods | FluView Interactive Influenza-Associated Pediatric Mortality


                            Five influenza-associated pediatric deaths were reported to CDC during week 17.

                            Four deaths occurred during the 2022-2023 season, bringing the total number of pediatric deaths for this season to 149. The deaths occurred during weeks 45, 49, and 51 (the weeks ending November 12, December 10, and December 24 of 2022). All four deaths were associated with influenza A viruses. One of the influenza A viruses had subtyping performed; it was an A(H3) virus.

                            One death occurred during week 10 of 2022 (the week ending March 12, 2022), which was during the 2021-2022 season. This death was associated with an influenza A(H3) virus. The total number of pediatric deaths that occurred in the 2021-2022 season is 46.

                            Click on image to launch interactive tool View Full Screen

                            Additional pediatric mortality surveillance information for current and past seasons:
                            Surveillance Methods | FluView Interactive Trend Indicators


                            Increasing:
                            Decreasing:
                            Stable: Indicators Status by System


                            Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                            Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                            Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                            HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                            NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

                            Additional National and International Influenza Surveillance Information


                            FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.

                            National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.

                            U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.

                            Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                            Comment


                            • #29
                              Weekly U.S. Influenza Surveillance Report


                              Print
                              Updated May 12, 2023

                              Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                              Key Updates for Week 18, ending May 6, 2023

                              Seasonal influenza activity remains low nationally. Viruses


                              Clinical Lab 0.9%

                              (Trend )


                              positive for influenza
                              this week


                              Public Health Lab
                              Influenza B viruses were the most frequently reported this week.

                              Virus Characterization
                              Genetic and antigenic characterization and antiviral susceptibility are summarized in this report. Illness


                              Outpatient Respiratory Illness 2.0%

                              (Trend )


                              of visits to a health care provider this week were for respiratory illness
                              (below baseline).


                              Outpatient Respiratory Illness: Activity Map
                              This week 1 jurisdiction experienced moderate activity and 1 jurisdiction experienced high or very high activity.

                              Long-term Care Facilities 0.3%

                              (Trend )


                              of facilities reported
                              ≥ 1 influenza-positive test
                              among residents this week.


                              FluSurv-NET 62.6 per 100,000


                              cumulative hospitalization rate

                              HHS Protect Hospitalizations 920

                              (Trend )


                              patients admitted to hospitals with influenza
                              this week.


                              NCHS Mortality 6.9%

                              (Trend )


                              of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                              Pediatric Deaths 1


                              deaths were reported this week for a total of
                              150 so far this season


                              All data are preliminary and may change as more reports are received.

                              Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                              A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                              Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                              Key Points
                              • Seasonal influenza activity remains low nationally.
                              • Nationally, outpatient respiratory illness is below baseline, and nine of 10 HHS regions are below their respective baselines.
                              • The number of flu hospital admissions remains low.
                              • During week 18, 48.6% of viruses reported by public health laboratories were influenza A and 51.4% were influenza B. Of the 12 influenza A viruses detected and subtyped during week 18, 3 were influenza A(H3N2) and 9 were influenza A(H1N1).
                              • One influenza-associated pediatric death that occurred during the 2022-2023 season was reported this week, for a total of 150 pediatric flu deaths reported so far this season.
                              • CDC estimates that, so far this season, there have been at least 27 million illnesses, 290,000 hospitalizations, and 19,000 deaths from flu.
                              • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                              • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                              • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                              • There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.
                              U.S. Virologic Surveillance


                              Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses. Clinical Laboratories


                              The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
                              No. of specimens tested 41,964 3,311,991
                              No. of positive specimens (%) 390 (0.9%) 351,710 (10.6%)
                              Positive specimens by type
                              Influenza A 159 (40.8%) 345,229 (98.2%)
                              Influenza B 231 (59.2%) 6,481 (1.8%)
                              INFLUENZA Virus Isolated

                              View Chart Data | View Full Screen Public Health Laboratories


                              The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                              No. of specimens tested 3,553 241,869
                              No. of positive specimens 35 29,109
                              Positive specimens by type/subtype
                              Influenza A 17 (48.6%) 28,464 (97.8%)
                              (H1N1)pdm09 9 (75.0%) 6,461 (27.0%)
                              H3N2 3 (25.0%) 17,469 (73.0%)
                              H3N2v 0 1 (<0.1%)
                              Subtyping not performed 5 4,533
                              Influenza B 18 (51.4%) 645 (2.2%)
                              Yamagata lineage 0 0
                              Victoria lineage 11 (100%) 485 (100%)
                              Lineage not performed 7 160

                              INFLUENZA Virus Isolated
                              View Chart Data | View Full Screen

                              Additional virologic surveillance information for current and past seasons:
                              Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data Influenza Virus Characterization


                              CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                              CDC genetically characterized 2,837 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2, but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2, and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                              A/H1 1,038
                              6B.1A.5a 1,038 (100%) 1 6 (0.6%)
                              2a 160 (15.4%)
                              2a.1 872 (84.0%)
                              A/H3 1,631
                              3C.2a1b.2a 1,631 (100%) 2a 25 (1.5%)
                              2a.1 184 (11.3%)
                              2a.1b 136 (8.3%)
                              2a.3 46 (2.8%)
                              2a.3a 3 (0.2%)
                              2a.3a.1 71 (4.4%)
                              2a.3b 11 (0.7%)
                              2b 1,155 (70.8%)
                              2c 0 (0%)
                              B/Victoria 168
                              V1A 168 (100%) 3 4 (2.4%)
                              3a.2 164 (97.6%)
                              B/Yamagata 0
                              Y3 0 Y3 0 (0%)

                              CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria, and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                              Influenza A Viruses
                              • A (H1N1)pdm09: Two hundred and thirty-four A(H1N1)pdm09 viruses were antigenically characterized by HI, and 230 (98%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines.
                              • A (H3N2): Two hundred and three A(H3N2) viruses were antigenically characterized by HINT, and 191 (94%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                              Influenza B Viruses
                              • B/Victoria: Fifty-six influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                              • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                              Assessment of Virus Susceptibility to Antiviral Medications

                              CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                              Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                              Neuraminidase
                              Inhibitors
                              Oseltamivir Viruses
                              Tested
                              2,831 1,035 1,629 167 0
                              Reduced
                              Inhibition
                              1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                              Highly
                              Reduced
                              Inhibition
                              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                              Peramivir Viruses
                              Tested
                              2,831 1,035 1,629 167 0
                              Reduced
                              Inhibition
                              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                              Highly
                              Reduced
                              Inhibition
                              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                              Zanamivir Viruses
                              Tested
                              2,831 1,035 1,629 167 0
                              Reduced
                              Inhibition
                              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                              Highly
                              Reduced
                              Inhibition
                              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                              PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                              Tested
                              2,746 992 1,589 165 0
                              Reduced
                              Susceptibility
                              0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                              One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir. Outpatient Respiratory Illness Surveillance


                              The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking COVID-19 activity in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website. Outpatient Respiratory Illness Visits


                              Nationwide during week 18, 2.0% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable (change of ≤ 0.1 percentage points) compared to week 17 and is below the national baseline of 2.5%. Nine of 10 HHS regions are below their respective baselines; Region 9 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.

                              national levels of ILI and ARI

                              * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                              View Chart Data (current season only) | View Full Screen Outpatient Respiratory Illness Visits by Age Group


                              More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                              The percentage of visits for respiratory illness reported in ILINet remained stable (change of ≤ 0.1 percentage point) for all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years) in week 18 compared to week 17.

                              national levels of ILI and ARI by age group

                              View Chart Data | View Full Screen Outpatient Respiratory Illness Activity Map


                              Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                              Week 18
                              (Week ending
                              May 6, 2023)
                              Week 17
                              (Week ending
                              Apr. 29, 2023)
                              Week 18
                              (Week ending
                              May 6, 2023)
                              Week 17
                              (Week ending
                              Apr. 29, 2023)
                              Very High 0 0 0 0
                              High 1 1 8 7
                              Moderate 1 3 19 14
                              Low 5 2 49 53
                              Minimal 48 49 596 616
                              Insufficient Data 0 0 257 239



                              *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                              Additional information about medically attended visits for ILI for current and past seasons:
                              Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map Long-term Care Facility (LTCF) Surveillance


                              LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 18, 36 (0.3%) of 14,370 facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 17.

                              national levels of ltcf influenza
                              View Chart Data | View Full Screen

                              Additional information about long-term care facility surveillance:
                              Surveillance Methods | Additional Data Hospitalization Surveillance

                              FluSurv-NET


                              The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 13 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

                              A total of 18,316 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and April 30, 2023. The weekly hospitalization rate observed in week 17, the last week of FluSurv-NET enrollment for the 2022-2023 season, was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season which peaked during week 52 (week ending December 27, 2014).

                              The overall cumulative hospitalization rate was 62.6 per 100,000 population. This cumulative hospitalization rate is similar to the hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                              When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (186.5). Among adults aged 65 and older, rates were highest among adults aged 85 and older (337.7). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (80.5), followed by adults aged 50-64 years (68.0). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (87.5), followed by non-Hispanic American Indian or Alaska Native persons (81.2), Hispanic/Latino persons (54.5), non-Hispanic White persons (53), and non-Hispanic Asian/Pacific Islander persons (27.2).

                              Among 18,316 hospitalizations, 17,504 (95.6%) were associated with influenza A virus, 641 (3.5%) with influenza B virus, 30 (0.2%) with influenza A virus and influenza B virus co-infection, and 141 (0.8%) with influenza virus for which the type was not determined. Among 4,559 hospitalizations with influenza A subtype information, 3,407 (74.7%) were A(H3N2), and 1,152 (25.2%) were A(H1N1)pdm09. Based on preliminary data, of the 5,471 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.7% (95% CI: 3.1%-4.4%) also tested positive for SARS-CoV-2.

                              Among 3,796 hospitalized adults with information on underlying medical conditions, 97.1% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 1,413 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 36.9% were pregnant. Among 1,330 hospitalized children with information on underlying medical conditions, 66.3% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease and obesity.

                              While patients admitted after April 30, 2023, will not be included, data on patients admitted through April 30, 2023, will continue to be updated as additional information is received.

                              FluSurvNet Cumulative Rates

                              View Full Screen

                              FluSurvNet Characteristics

                              View Full Screen

                              Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                              Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive HHS Protect Hospitalization Surveillance


                              Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 18, 920 patients with laboratory-confirmed influenza were admitted to a hospital. The number of patients admitted to a hospital with laboratory-confirmed influenza remained stable compared to week 17.

                              national levels of influenza hospitalizations
                              View Chart Data | View Full Screen

                              Additional HHS Protect hospitalization surveillance information:
                              Surveillance Methods | Additional Data Mortality Surveillance

                              National Center for Health Statistics (NCHS) Mortality Surveillance


                              Based on NCHS mortality surveillance data available on May 11, 2023, 6.9% of the deaths that occurred during the week ending May 6, 2023 (week 18), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage decreased (> 0.3 percentage point change) compared to week 17 and is above the epidemic threshold of 6.7% for this week. Among the 1,464 PIC deaths reported for this week, 376 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 11 listed influenza. The data presented are preliminary and may change as more data are received and processed.

                              Click on image to launch interactive toolView Chart Data | View Full Screen

                              Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                              Surveillance Methods | FluView Interactive Influenza-Associated Pediatric Mortality


                              One influenza-associated pediatric death occurring during the 2022-2023 season was reported to CDC during week 18. The death was associated with an influenza A(H3) virus and occurred during week 50 of 2022 (the week ending December 17, 2022).

                              A total of 150 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

                              Click on image to launch interactive tool View Full Screen

                              Additional pediatric mortality surveillance information for current and past seasons:
                              Surveillance Methods | FluView Interactive Trend Indicators


                              Increasing:
                              Decreasing:
                              Stable: Indicators Status by System


                              Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                              Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                              Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                              HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                              NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

                              Additional National and International Influenza Surveillance Information


                              FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.

                              National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.

                              U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.

                              Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                              Comment


                              • #30
                                Weekly U.S. Influenza Surveillance Report


                                Print
                                Updated May 26, 2023

                                Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

                                Key Updates for Week 20, ending May 20, 2023

                                Seasonal influenza activity remains low nationally.

                                This is the last full FluView report of the 2022-2023 season. An abbreviated report will be published during the summer, and the first full report of the 2023-2024 season will be published on October 13, 2023. Viruses


                                Clinical Lab 1.1%

                                (Trend )


                                positive for influenza
                                this week


                                Public Health Lab
                                Influenza B viruses were the most frequently reported this week.

                                Virus Characterization
                                Genetic and antigenic characterization and antiviral susceptibility are summarized in this report. Illness


                                Outpatient Respiratory Illness 2.0%

                                (Trend )


                                of visits to a health care provider this week were for respiratory illness
                                (below baseline).


                                Outpatient Respiratory Illness: Activity Map
                                This week 1 jurisdiction experienced moderate activity and 2 jurisdictions experienced high activity.

                                Long-term Care Facilities 0.3%

                                (Trend )


                                of facilities reported
                                ≥ 1 influenza-positive test
                                among residents this week.


                                FluSurv-NET 62.6 per 100,000


                                cumulative hospitalization rate

                                HHS Protect Hospitalizations 939

                                (Trend )


                                patients admitted to hospitals with influenza
                                this week.


                                NCHS Mortality 6.5%

                                (Trend )


                                of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

                                Pediatric Deaths 2


                                deaths were reported this week for a total of
                                154 so far this season


                                All data are preliminary and may change as more reports are received.

                                Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

                                A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.

                                Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

                                Key Points
                                • Seasonal influenza activity remains low nationally.
                                • This week is the last full version of FluView for the 2022-2023 influenza season. Starting with week 21, an abbreviated summer version of FluView will be published. The full version is expected to resume for week 40 of 2023, which is the start of the 2023-2024 influenza season.
                                • Nationally, outpatient respiratory illness is below baseline, and eight of 10 HHS regions are below their respective baselines.
                                • The number of flu hospital admissions remains low.
                                • During week 20, 36.1% of the 36 viruses reported by public health laboratories were influenza A and 63.9% were influenza B. All six influenza A viruses detected and subtyped during week 20 were influenza A(H1N1).
                                • Two influenza-associated pediatric death that occurred during the 2022-2023 season were reported this week, for a total of 154 pediatric flu deaths reported so far this season.
                                • CDC estimates that, so far this season, there have been at least 27 million illnesses, 300,000 hospitalizations, and 19,000 deaths from flu.
                                • The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
                                • All viruses collected and evaluated this season have been susceptible to the influenza antivirals peramivir, zanamivir, and baloxavir, and all viruses except for one (> 99.9%) have been susceptible to the influenza antiviral oseltamivir.
                                • CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
                                U.S. Virologic Surveillance


                                Nationally, the percentage of specimens testing positive for influenza in clinical laboratories remained stable (change of <0.5 percentage points). For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included, as they are not circulating influenza viruses. Clinical Laboratories


                                The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
                                No. of specimens tested 31,894 3,395,600
                                No. of positive specimens (%) 355 (1.1%) 352,572 (10.4%)
                                Positive specimens by type
                                Influenza A 108 (30.4%) 345,544 (98.0%)
                                Influenza B 247 (69.6%) 7,028 (2.0%)
                                INFLUENZA Virus Isolated

                                View Chart Data | View Full Screen Public Health Laboratories


                                The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
                                No. of specimens tested 2,780 248,451
                                No. of positive specimens 36 29,364
                                Positive specimens by type/subtype
                                Influenza A 13 (36.1%) 28,582 (97.3%)
                                (H1N1)pdm09 6 (100%) 6,545 (27.2%)
                                H3N2 0 (0%) 17,500 (72.8%)
                                H3N2v 0 1 (<0.1%)
                                Subtyping not performed 7 4,536
                                Influenza B 23 (63.9%) 782 (2.7%)
                                Yamagata lineage 0 0
                                Victoria lineage 17 (100%) 593 (100%)
                                Lineage not performed 6 189

                                INFLUENZA Virus Isolated
                                View Chart Data | View Full Screen

                                Additional virologic surveillance information for current and past seasons:
                                Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data Influenza Virus Characterization


                                CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans.

                                CDC genetically characterized 2,912 influenza viruses collected since October 2, 2022. To reflect the genetic diversity of the HA genes in recent A(H1N1)pdm09 and A(H3N2) viruses, new subclades have been designated. The vast majority of A(H1N1)pdm09 viruses collected in the U.S. this season express HA genes belonging to 6B.1A.5a.2, but this clade has been split into the 2a and 2a.1 subclades. All A(H3N2) viruses collected thus far in the U.S. this season express HA genes belonging to clade 3C.2a1b.2a.2, and this clade has been split into multiple subclades. The new subclade designations improve the ability to track the evolution and co-circulation of multiple groups of influenza viruses.
                                A/H1 1,062
                                6B.1A.5a 1,062 (100%) 1 6 (0.6%)
                                2a 166 (15.6%)
                                2a.1 890 (83.8%)
                                A/H3 1,634
                                3C.2a1b.2a 1,634 (100%) 2a 25 (1.5%)
                                2a.1 185 (11.3%)
                                2a.1b 137 (8.4%)
                                2a.3 45 (2.8%)
                                2a.3a 3 (0.2%)
                                2a.3a.1 71 (4.3%)
                                2a.3b 11 (0.7%)
                                2b 1,157 (70.8%)
                                2c 0 (0%)
                                B/Victoria 216
                                V1A 216 (100%) 3 5 (2.3%)
                                3a.2 211 (97.7%)
                                B/Yamagata 0
                                Y3 0 Y3 0 (0%)

                                CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria, and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2022-2023 Northern Hemisphere recommended cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.

                                Influenza A Viruses
                                • A (H1N1)pdm09: Three hundred and fourteen A(H1N1)pdm09 viruses were antigenically characterized by HI, and 310 (99%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines.
                                • A (H3N2): Two hundred and twenty-five A(H3N2) viruses were antigenically characterized by HINT, and 212 (94%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

                                Influenza B Viruses
                                • B/Victoria: Fifty-eight influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
                                • B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

                                Assessment of Virus Susceptibility to Antiviral Medications

                                CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.

                                Viruses collected in the U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:
                                Neuraminidase
                                Inhibitors
                                Oseltamivir Viruses
                                Tested
                                2,904 1,059 1,630 215 0
                                Reduced
                                Inhibition
                                1 (<0.1%) 1 (0.1%) 0 (0%) 0 (0%) 0 (0%)
                                Highly
                                Reduced
                                Inhibition
                                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                                Peramivir Viruses
                                Tested
                                2,904 1,059 1,630 215 0
                                Reduced
                                Inhibition
                                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                                Highly
                                Reduced
                                Inhibition
                                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                                Zanamivir Viruses
                                Tested
                                2,904 1,059 1,630 215 0
                                Reduced
                                Inhibition
                                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                                Highly
                                Reduced
                                Inhibition
                                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                                PA Cap-Dependent Endonuclease Inhibitor Baloxavir Viruses
                                Tested
                                2,820 1,016 1,593 211 0
                                Reduced
                                Susceptibility
                                0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
                                One A(H1N1)pdm09 virus had NA-S247G amino acid substitution and showed reduced inhibition by oseltamivir. Outpatient Respiratory Illness Surveillance


                                The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking COVID-19 activity in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website. Outpatient Respiratory Illness Visits


                                Nationwide during week 20, 2.0% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has remained stable (change of ≤ 0.1 percentage points) compared to week 19 and is below the national baseline of 2.5%. Eight of 10 HHS regions are below their respective baselines; Region 2 is above its baseline, and Region 9 is at its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.

                                national levels of ILI and ARI

                                * Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”

                                View Chart Data (current season only) | View Full Screen Outpatient Respiratory Illness Visits by Age Group


                                More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.

                                The percentage of visits for respiratory illness reported in ILINet remained stable (change of ≤ 0.1 percentage point) for all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years) in week 20 compared to week 19.

                                national levels of ILI and ARI by age group

                                View Chart Data | View Full Screen Outpatient Respiratory Illness Activity Map


                                Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
                                Week 20
                                (Week ending
                                May 20, 2023)
                                Week 19
                                (Week ending
                                May 13, 2023)
                                Week 20
                                (Week ending
                                May 20, 2023)
                                Week 19
                                (Week ending
                                May 13, 2023)
                                Very High 0 0 1 1
                                High 2 4 6 6
                                Moderate 1 0 12 15
                                Low 3 3 58 58
                                Minimal 49 48 585 606
                                Insufficient Data 0 0 267 243



                                *Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.

                                Additional information about medically attended visits for ILI for current and past seasons:
                                Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map Long-term Care Facility (LTCF) Surveillance


                                LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During 20, 43 (0.3%) of 14,074 facilities reported at least one influenza positive test among their residents. This percentage remains stable compared to week 19.

                                national levels of ltcf influenza
                                View Chart Data | View Full Screen

                                Additional information about long-term care facility surveillance:
                                Surveillance Methods | Additional Data Hospitalization Surveillance

                                FluSurv-NET


                                The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 13 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

                                A total of 18,306 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and April 30, 2023. The weekly hospitalization rate observed in week 17 the last week of FluSurv-NET enrollment for the 2023-2024 season, was 0.2 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-2018 season, which peaked during week 1 (week ending January 6, 2018) and the 2014-2015 season, which peaked during week 52 (week ending December 27, 2014).

                                The overall cumulative hospitalization rate was 62.6 per 100,000 population. This cumulative hospitalization rate is similar to the hospitalization rates for 4 seasons (2014-2015, 2016-2017, 2018-2019, and 2019-2020 seasons) and lower than the hospitalization rate for the 2017-2018 season, going back to 2010-2011.

                                When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (186.8). Among adults aged 65 and older, rates were highest among adults aged 85 and older (102.1). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (80.4), followed by adults aged 50-64 years (68.0). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (88.5), followed by non-Hispanic American Indian or Alaska Native persons (82.7), Hispanic/Latino persons (55.6), non-Hispanic White persons (54.1), and non-Hispanic Asian/Pacific Islander persons (27.7).

                                Among 18,306 hospitalizations, 17,487 (95.5%) were associated with influenza A virus, 649 (3.5%) with influenza B virus, 30 (0.2%) with influenza A virus and influenza B virus co-infection, and 140 (0.8%) with influenza virus for which the type was not determined. Among 4,564 hospitalizations with influenza A subtype information, 3,412 (74.8%) were A(H3N2), and 1,152 (25.3%) were A(H1N1)pdm09. Based on preliminary data, of the 5,689 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.7% (95% CI: 3.1%-4.4%) also tested positive for SARS-CoV-2.

                                Among 3,926 hospitalized adults with information on underlying medical conditions, 97.0% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 1,422 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 36.8% were pregnant. Among 1,385 hospitalized children with information on underlying medical conditions, 66.4% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease, and obesity.

                                While patients admitted after April 30, 2023, will not be included, data on patients admitted through April 30, 2023, will continue to be updated as additional information is received.

                                FluSurvNet Cumulative Rates

                                View Full Screen

                                FluSurvNet Characteristics

                                View Full Screen

                                Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
                                Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics | RESP-NET Interactive HHS Protect Hospitalization Surveillance


                                Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 20, 939 patients with laboratory-confirmed influenza were admitted to a hospital. The number of patients admitted to a hospital with laboratory-confirmed influenza remained stable compared to week 19.

                                national levels of influenza hospitalizations
                                View Chart Data | View Full Screen

                                Additional HHS Protect hospitalization surveillance information:
                                Surveillance Methods | Additional Data Mortality Surveillance

                                National Center for Health Statistics (NCHS) Mortality Surveillance


                                Based on NCHS mortality surveillance data available on May 25, 2023, 6.5% of the deaths that occurred during the week ending May 20, 2023 (week 20), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage remained stable (≤ 0.3 percentage point change) compared to week 19 and is above the epidemic threshold of 6.4% for this week. Among the 1,483 PIC deaths reported for this week, 304 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 15 listed influenza. The data presented are preliminary and may change as more data are received and processed.

                                Click on image to launch interactive toolView Chart Data | View Full Screen

                                Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
                                Surveillance Methods | FluView Interactive Influenza-Associated Pediatric Mortality


                                Two influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 20. One death was associated with an influenza A(H1N1) virus and the other death was associated with an influenza B virus with no lineage determined. Both deaths occurred during week 19 (the week ending May 13, 2023).

                                A total of 154 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

                                Click on image to launch interactive tool View Full Screen

                                Additional pediatric mortality surveillance information for current and past seasons:
                                Surveillance Methods | FluView Interactive Trend Indicators


                                Increasing:
                                Decreasing:
                                Stable: Indicators Status by System


                                Clinical Labs: Up or down arrows indicate a change of greater than or equal to 0.5 percentage points in the percent of specimens positive for influenza compared to the previous week.
                                Outpatient Respiratory Illness (ILINet): Up or down arrows indicate a change of greater than 0.1 percentage points in the percent of visits due to respiratory illness (ILI) compared to the previous week.
                                Long-term Care Facilities: Up or down arrows indicate change of greater than or equal to 5% of the percent of facilities reporting at least one influenza positive test among their residents compared to the previous week.
                                HHS Protect Hospitalizations: Up or down arrows indicate change of greater than or equal to 5% of the number of patients admitted with laboratory-confirmed influenza compared to the previous week.
                                NCHS Mortality: Up or down arrows indicate change of greater than 0.3 percentage points of the percent of deaths due to PIC compared to the previous week.

                                Additional National and International Influenza Surveillance Information


                                FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.

                                National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.

                                U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.

                                Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

                                Comment

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