Weekly U.S. Influenza Surveillance Report
Updated April 29, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 16, ending April 23, 2022
Seasonal influenza activity continues to increase in some areas of the country. The first human detection of avian influenza A(H5) in the United States was reported this week.
Viruses
Clinical Lab7.8%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness2.1%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 1 jurisdiction experienced moderate activity and 3 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.8%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET11.1 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations3,452
patients admitted to hospitals with influenza
this week.
NCHS Mortality6.8 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (at threshold)
Pediatric Deaths1
influenza-associated death reported this week for a total of 23 so far this season
All data are preliminary and may change as more reports are received.
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
Nationally, the percentage of specimens testing positive for influenza in clinical laboratories decreased. However, activity varied by region; percent positivity increased this week in Regions 4 and 10 compared with the previous week and decreased in Regions 1, 2, 3, 5, 6, 7, 8, and 9. Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 10,406 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 500 (4.8%) were also positive for SARS-CoV-2. 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.
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.
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
Novel Influenza A Virus:
The first detection of avian influenza A(H5) virus in a person in the U.S. who was exposed to H5N1-infected birds was reported by the Colorado Department of Public Health and Environment (CDPHE) and confirmed by the Centers for Disease Control and Prevention (CDC) on April 27, 2022.
On April 20, 2022, a person >18 years of age in Colorado developed fatigue following exposure to H5N1 virus-infected poultry while participating in poultry depopulation activities during April 18-22. The individual, who does not have any known chronic medical conditions, reported wearing recommended personal protective equipment although breaches of recommended eye protection were reported. An upper respiratory tract specimen was collected from the individual on April 20, 2022. The specimen arrived at the CDPHE Laboratory Services on April 22, 2022; testing was completed April 25, 2022. RT-PCR indicated it was positive for influenza A virus but lacked reactivity with RT-PCR tests for the hemagglutinin (HA) gene of contemporary seasonal influenza viruses of H1pdm09 or H3 subtypes. The specimen was forwarded to the Influenza Division of CDC for further testing, was received at CDC on April 27, 2022, and confirmed as influenza A(H5) virus using RT-PCR the same day. The A(H5)-positive individual denied any other symptoms, and fatigue resolved after 3 days, after which the individual returned to their baseline health. The individual remains asymptomatic in isolation on oseltamivir treatment. A second swab was collected on April 26, 2022, and confirmed to be negative for influenza on April 27, 2022, by the CDPHE Laboratory Services.
This is the first human to test positive for avian influenza A(H5) virus in the U.S.
During January 13, 2022, through April 27, 2022, USDA APHIS confirmed more than 899 detections of wild birds infected with HPAI A(H5N1) virus in 33 states. On February 9, 2022, USDA APHIS confirmed the first outbreak of HPAI A(H5N1) virus in a commercial turkey flock in Indiana. Since then, APHIS has identified 247 HPAI A(H5N1) outbreaks among commercial poultry or backyard bird flocks in 29 states involving more than 35 million birds.
State and local public health departments monitor people who were exposed to infected birds for onset of symptoms for 10 days following the last date of exposure. People who develop symptoms are tested for influenza. As of April 23, 2022, over 2,500 people have been actively monitored for symptoms following exposure to infected birds. This is the first human detection of avian influenza A(H5) in the U.S.
Additional novel influenza information for current and past seasons:
Surveillance Methods | FluView Interactive: Novel Influenza
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using 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 also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 1,034 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
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 2021-2022 Northern Hemisphere recommended egg-based and 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
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 United States since October 3, 2021, were tested for antiviral susceptibility as follows:
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for 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, 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. Five of the 10 HHS regions are below their region-specific baselines; Regions 1, 2, and 8 are above their respective baselines, while Regions 7 and 10 are at their 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 ScreenOutpatient 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 one age group (0-4 years) while remaining stable in all other age groups (5-24 years, 25-49 years, 50-64 years, and 65+ years) compared to the previous week. The percentage of visits for respiratory illness has been trending upward in all age groups since February (0-4 years, 5-24 years) and March (25-49 years, 50-64 years, and 65+ years).
* 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 | 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).
*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, 108 (0.8%) of 14,086 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
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 3,262 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and April 23, 2022. The overall cumulative hospitalization rate was 11.1 per 100,000 population. This cumulative hospitalization rate is higher than the end-of-season cumulative hospitalization rate observed in week 16 during the 2020-2021 season (0.8 per 100,000) and 2011-2012 seasons (8.7 per 100,000), but lower than the in-season rates observed in week 16 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 62.7 to 105.3 per 100,000 during the 2016-17 through 2019-20 seasons). After peaking during the week ending January 1, 2022 (MMWR week 52), weekly hospitalization rates declined through the week ending February 19, 2022 (MMWR week 7), before increasing again. The overall weekly rate observed during the week ending April 9, 2022 (1.0) was greater than the peak weekly rate observed during the week ending January 1, 2022 (0.9).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (31.3). Among adults aged 65 and older, rates were highest among adults aged 85 and older (60.6). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (14.7) followed by adults aged 50-64 years (10.3). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (15.7), followed by non-Hispanic Black persons (13.1).
Among 3,262 hospitalizations, 3,135 (96.1%) were associated with influenza A virus, 109 (3.3%) with influenza B virus, 6 (0.2%) with influenza A virus and influenza B virus co-infection, and 12 (0.4%) with influenza virus for which the type was not determined. Among 790 hospitalizations with influenza A subtype information, 781 (98.9%) were A(H3N2), and 9 (1.1%) were A(H1N1)pdm09. Based on preliminary data, of the 3,262 laboratory-confirmed influenza-associated hospitalizations, 2.7% also tested positive for SARS-CoV-2.
Among 1,534 hospitalized adults with information on underlying medical conditions, 93.5% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 230 hospitalized children with information on underlying medical conditions, 69.1% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
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
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 16, 3,452 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQs pdf icon[680 KB, 52 pages]external icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on April 28, 2022, 6.8% of the deaths that occurred during the week ending April 23, 2022 (week 16), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is equal to the epidemic threshold of 6.8% for this week. Among the 1,293 PIC deaths reported for this week, 434 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 33 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | 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 2021-2022 season was reported to CDC during week 16. The death was associated with an influenza A virus for which no subtyping was performed and occurred during week 15 (the week ending April 16, 2022).
A total of 23 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
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.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 29, 2022, 11:00 AM
Content source: Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
Updated April 29, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 16, ending April 23, 2022
Seasonal influenza activity continues to increase in some areas of the country. The first human detection of avian influenza A(H5) in the United States was reported this week.
Viruses
Clinical Lab7.8%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness2.1%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 1 jurisdiction experienced moderate activity and 3 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.8%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET11.1 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations3,452
patients admitted to hospitals with influenza
this week.
NCHS Mortality6.8 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (at threshold)
Pediatric Deaths1
influenza-associated death reported this week for a total of 23 so far this season
All data are preliminary and may change as more reports are received.
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
- Influenza activity varies by region. Influenza activity continues to increase in some areas of the country.
- The first human detection of avian influenza A(H5) in the U.S. was reported this week.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness remained stable compared to last week and is below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased each week for the past 12 weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the end-of-seasons rates for the 2020-2021 and 2011-2012 seasons, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- One influenza-associated pediatric death was reported this week. There have been 23 pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 5.3 million flu illnesses, 53,000 hospitalizations, and 3,200 deaths from flu.
- An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- There are also prescription flu antiviral drugs that can be used to treat flu illness.
Nationally, the percentage of specimens testing positive for influenza in clinical laboratories decreased. However, activity varied by region; percent positivity increased this week in Regions 4 and 10 compared with the previous week and decreased in Regions 1, 2, 3, 5, 6, 7, 8, and 9. Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 10,406 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 500 (4.8%) were also positive for SARS-CoV-2. 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 | 44,994 | 2,195,426 |
| No. of positive specimens (%) | 3,494 (7.8%) | 84,202 (3.8%) |
| Positive specimens by type | ||
| Influenza A | 3,451 (98.8%) | 82,732 (98.3%) |
| Influenza B | 43 (1.2%) | 1,470 (1.7%) |
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 | 11,721 | 768,531 |
| No. of positive specimens | 402 | 18,682 |
| Positive specimens by type/subtype | ||
| Influenza A | 399 (99.3%) | 18,572 (99.4%) |
| (H1N1)pdm09 | 2 (0.7%) | 11 (0.1%) |
| H3N2 | 269 (99.3%) | 14,381 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 128 | 4,179 |
| Influenza B | 3 (0.7%) | 110 (0.6%) |
| Yamagata lineage | 0 | 1 (2.8%) |
| Victoria lineage | 0 | 35 (97.2%) |
| Lineage not performed | 3 | 74 |
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
Novel Influenza A Virus:
The first detection of avian influenza A(H5) virus in a person in the U.S. who was exposed to H5N1-infected birds was reported by the Colorado Department of Public Health and Environment (CDPHE) and confirmed by the Centers for Disease Control and Prevention (CDC) on April 27, 2022.
On April 20, 2022, a person >18 years of age in Colorado developed fatigue following exposure to H5N1 virus-infected poultry while participating in poultry depopulation activities during April 18-22. The individual, who does not have any known chronic medical conditions, reported wearing recommended personal protective equipment although breaches of recommended eye protection were reported. An upper respiratory tract specimen was collected from the individual on April 20, 2022. The specimen arrived at the CDPHE Laboratory Services on April 22, 2022; testing was completed April 25, 2022. RT-PCR indicated it was positive for influenza A virus but lacked reactivity with RT-PCR tests for the hemagglutinin (HA) gene of contemporary seasonal influenza viruses of H1pdm09 or H3 subtypes. The specimen was forwarded to the Influenza Division of CDC for further testing, was received at CDC on April 27, 2022, and confirmed as influenza A(H5) virus using RT-PCR the same day. The A(H5)-positive individual denied any other symptoms, and fatigue resolved after 3 days, after which the individual returned to their baseline health. The individual remains asymptomatic in isolation on oseltamivir treatment. A second swab was collected on April 26, 2022, and confirmed to be negative for influenza on April 27, 2022, by the CDPHE Laboratory Services.
This is the first human to test positive for avian influenza A(H5) virus in the U.S.
During January 13, 2022, through April 27, 2022, USDA APHIS confirmed more than 899 detections of wild birds infected with HPAI A(H5N1) virus in 33 states. On February 9, 2022, USDA APHIS confirmed the first outbreak of HPAI A(H5N1) virus in a commercial turkey flock in Indiana. Since then, APHIS has identified 247 HPAI A(H5N1) outbreaks among commercial poultry or backyard bird flocks in 29 states involving more than 35 million birds.
State and local public health departments monitor people who were exposed to infected birds for onset of symptoms for 10 days following the last date of exposure. People who develop symptoms are tested for influenza. As of April 23, 2022, over 2,500 people have been actively monitored for symptoms following exposure to infected birds. This is the first human detection of avian influenza A(H5) in the U.S.
Additional novel influenza information for current and past seasons:
Surveillance Methods | FluView Interactive: Novel Influenza
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using 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 also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 1,034 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 4 | ||||
| 6B.1A | 4 (100%) | 5a.1 | 2 (50%) | ||
| 5a.2 | 2 (50%) | ||||
| A/H3 | 1,007 | ||||
| 3C.2a1b | 1,007 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 1,005 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 23 | ||||
| V1A | 23 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (39.1%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 14 (60.9%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
Influenza A Viruses
- A (H1N1)pdm09: Three A(H1N1)pdm09 viruses were antigenically characterized by HI, and 2 (67%) 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 and 2 (67%) were well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of 93 A(H3N2) viruses were antigenically characterized by HINT, and 4 (4%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 19 (20%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Fifteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (73%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (73%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
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 United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 1,168 | 5 | 1,140 | 23 | 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%) | ||
| Peramivir | Viruses Tested | 1,168 | 5 | 1,140 | 23 | 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 | 1,168 | 5 | 1,140 | 23 | 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 | 1,139 | 5 | 1,111 | 23 | 0 |
| Reduced Susceptibility | 1 (0.1%) | (0.0%) | 1 (0.1%) | (0.0%) | (0.0%) |
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for 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, 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. Five of the 10 HHS regions are below their region-specific baselines; Regions 1, 2, and 8 are above their respective baselines, while Regions 7 and 10 are at their 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 ScreenOutpatient 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 one age group (0-4 years) while remaining stable in all other age groups (5-24 years, 25-49 years, 50-64 years, and 65+ years) compared to the previous week. The percentage of visits for respiratory illness has been trending upward in all age groups since February (0-4 years, 5-24 years) and March (25-49 years, 50-64 years, and 65+ years).
* 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 | 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. 23, 2022) | Week 15 (Week ending Apr. 16, 2022) | Week 16 (Week ending Apr. 23, 2022) | Week 15 (Week ending Apr. 16, 2022) | |
| Very High | 1 | 0 | 1 | 3 |
| High | 2 | 3 | 12 | 11 |
| Moderate | 1 | 3 | 25 | 23 |
| Low | 9 | 11 | 92 | 86 |
| Minimal | 41 | 38 | 534 | 541 |
| Insufficient Data | 1 | 0 | 265 | 265 |
*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, 108 (0.8%) of 14,086 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
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 3,262 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and April 23, 2022. The overall cumulative hospitalization rate was 11.1 per 100,000 population. This cumulative hospitalization rate is higher than the end-of-season cumulative hospitalization rate observed in week 16 during the 2020-2021 season (0.8 per 100,000) and 2011-2012 seasons (8.7 per 100,000), but lower than the in-season rates observed in week 16 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 62.7 to 105.3 per 100,000 during the 2016-17 through 2019-20 seasons). After peaking during the week ending January 1, 2022 (MMWR week 52), weekly hospitalization rates declined through the week ending February 19, 2022 (MMWR week 7), before increasing again. The overall weekly rate observed during the week ending April 9, 2022 (1.0) was greater than the peak weekly rate observed during the week ending January 1, 2022 (0.9).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (31.3). Among adults aged 65 and older, rates were highest among adults aged 85 and older (60.6). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (14.7) followed by adults aged 50-64 years (10.3). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (15.7), followed by non-Hispanic Black persons (13.1).
Among 3,262 hospitalizations, 3,135 (96.1%) were associated with influenza A virus, 109 (3.3%) with influenza B virus, 6 (0.2%) with influenza A virus and influenza B virus co-infection, and 12 (0.4%) with influenza virus for which the type was not determined. Among 790 hospitalizations with influenza A subtype information, 781 (98.9%) were A(H3N2), and 9 (1.1%) were A(H1N1)pdm09. Based on preliminary data, of the 3,262 laboratory-confirmed influenza-associated hospitalizations, 2.7% also tested positive for SARS-CoV-2.
Among 1,534 hospitalized adults with information on underlying medical conditions, 93.5% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 230 hospitalized children with information on underlying medical conditions, 69.1% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
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
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 16, 3,452 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQs pdf icon[680 KB, 52 pages]external icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on April 28, 2022, 6.8% of the deaths that occurred during the week ending April 23, 2022 (week 16), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is equal to the epidemic threshold of 6.8% for this week. Among the 1,293 PIC deaths reported for this week, 434 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 33 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | 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 2021-2022 season was reported to CDC during week 16. The death was associated with an influenza A virus for which no subtyping was performed and occurred during week 15 (the week ending April 16, 2022).
A total of 23 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
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.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 29, 2022, 11:00 AM
Content source: Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
