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How CDC is monitoring influenza data among people to better understand the current avian influenza A (H5N1) situation
Weekly Snapshot for Week Ending November 2, 2024
At a glance
CDC influenza (flu) surveillance systems show no indicators of unusual influenza activity in people, including avian influenza A(H5N1). Overview
This page provides information on how CDC systems that monitor national, state, and local level influenza data are being used during the current avian influenza A(H5N1) situation.
Influenza virus and illness activity are monitored year-round through a collaborative effort between CDC and many partners, including state, local, and territorial health departments; public health and clinical laboratories; clinics; and emergency departments.
Human cases of novel influenza, which are human infections with non-human influenza A viruses that are different from currently spreading seasonal human influenza viruses, are nationally notifiable. Every identified case is investigated and reported to CDC.
CDC is actively looking at multiple flu indicators during the current situation to monitor for influenza A(H5N1) viruses, including looking for spread of the virus to, or among people, in jurisdictions where the virus has been identified in people or animals.
Region 9 - San Francisco
Arizona, California, Hawaii, Nevada,
American Samoa, Commonwealth of the
Northern Mariana Islands, Federated States
of Micronesia, Guam, Marshall Islands, and
Republic of Palau
Update: Influenza Positive Tests Reported to CDC by Public Health Laboratories,
HHS Region 9, 2024-25 Season, week ending Nov 02, 2024 Region 9 - San Francisco
Arizona, California, Hawaii, Nevada,
American Samoa, Commonwealth of the
Northern Mariana Islands, Federated States
of Micronesia, Guam, Marshall Islands, and
Republic of Palau
Update: Influenza Positive Tests Reported to CDC by Public Health Laboratories,
HHS Region 8, 2024-25 Season, week ending Nov 02, 2024 Region 8 - Denver
Colorado, Montana, North Dakota, South
Dakota, Utah, and Wyoming
This page provides information on how CDC systems that monitor national, state, and local level influenza data are being used during the current avian influenza A(H5N1) situation....
Excerpts:
Main Findings from Surveillance Systems
CDC has multiple surveillance systems that are used year-round to monitor key flu indicators. These data are reviewed comprehensively each week. Taken together, as of November 14, 2024, these systems currently show no indicators of unusual flu activity in people, including avian influenza A(H5N1) viruses.
-snip-
Public health laboratory reporting
Public health laboratories use CDC's diagnostic tools to detect both seasonal influenza viruses and novel influenza A viruses including influenza A(H5). These diagnostic tools are used at more than 100 public health laboratories in all 50 U.S. states. The results of tests performed by these public health laboratories nationwide are summarized below.
Region 10 - Seattle
Alaska, Idaho, Oregon, and Washington
Update: Influenza Positive Tests Reported to CDC by Public Health Laboratories,
HHS Region 9, 2024-25 Season, week ending Nov 09, 2024
Region 9 - San Francisco
Arizona, California, Hawaii, Nevada,
American Samoa, Commonwealth of the
Northern Mariana Islands, Federated States
of Micronesia, Guam, Marshall Islands, and
Republic of Palau
National, Regional, and State Level Outpatient Illness and Viral Surveillance
Influenza Positive Tests Reported to CDC by Public Health Laboratories, HHS Region 9,
2024-25 Season, week ending Nov 09, 2024
Reported by: U.S. WHO/NREVSS Collaborating Laboratories and ILINet
Influenza Positive Tests Reported to CDC by Public Health Laboratories, HHS Region 10,
2024-25 Season, week ending Nov 09, 2024
Reported by: U.S. WHO/NREVSS Collaborating Laboratories and ILINet
52 Confirmed Total Reported Human Cases in the United States
Current Situation Confirmed human case summary during the 2024 outbreak, by state and exposure source
NOTE: One additional case was previously detected in a poultry worker in Colorado in 2022.
Additional cases meeting the Council of State and Territorial Epidemiologists (CSTE) probable case definition have been reported by states: 1 case with dairy cow exposure (CA), 3 cases with poultry exposure (WA). Confirmatory testing at CDC for these cases was negative.
[bolding is mine] H5 Bird Flu: Current Situation
CDC A(H5N1) Bird Flu Response Update November 18, 2024
Situation Update
November 18, 2024 – CDC continues to respond to the public health challenge posed by a multistate outbreak of avian influenza A(H5N1) virus, or "H5N1 bird flu," in dairy cows, poultry and other animals in the United States. CDC is working in collaboration with the U.S. Department of Agriculture (USDA), the Food and Drug Administration (FDA), Administration for Strategic Preparedness and Response (ASPR), state public health and animal health officials, and other partners using a One Health approach.
Since April 2024, CDC, working with state public health departments, has confirmed avian influenza A(H5) virus infections in 52 people in the United States. Twenty-one of these cases were associated with exposure to avian influenza A(H5N1) virus -infected poultry and 30 were associated with exposure to infected dairy cows [A]. The source of the exposure in one case, which was reported by Missouri on September 6, could not be determined.
The 52 cases include 26 cases among dairy farm workers in California, five of which were confirmed by CDC on November 13 and 14, and one additional case in a poultry farm worker in Oregon. This is the first human case of H5N1 bird flu reported in Oregon. All recent cases have occurred in workers on affected farms. All available data so far suggest sporadic instances of animal-to-human spread. These farm workers all described mild symptoms, many with eye redness or discharge (conjunctivitis). Some workers who tested positive in Washington reported some mild upper respiratory symptoms. None of the workers were hospitalized.
CDC is aware of the human case of H5N1 bird flu reported in Canada and is in communication with the Public Health Agency of Canada (PHAC), which has confirmed that the case was caused by an H5N1 virus that is different than those causing outbreaks in dairy cows and other animals in the United States. More information about the case in Canada and ongoing epidemiological investigation is available in a statement from PHAC. Updated case counts for the United States, including by state and source of exposure, are recorded in a table on CDC's website. To date, person-to-person spread of H5 bird flu has not been identified in the United States. CDC believes the immediate risk to the general public from H5 bird flu remains low, but people with exposure to infected animals are at higher risk of infection.
On the animal health side, since March 2024, USDA has confirmed infected cattle in 505 dairy herds in 15 U.S. states. The number of affected herds continues to grow nationally, with almost all new infections identified in herds in California. USDA reports that, since April 2024, there have been H5 detections in 50 commercial poultry flocks and 38 backyard flocks, for a total of 25.61 million birds affected.
Among other activities reported in previous spotlights and ongoing, recent highlights of CDC's response to this include:
Laboratory Update
To date, CDC has confirmed 11 human cases of H5 bird flu in poultry farm workers in Washington. Genetic sequencing of influenza virus from clinical specimens from these cases showed no changes in the hemagglutinin (HA) associated with increased infectivity or transmissibility among people. However, in influenza specimens from three of these H5 cases, CDC identified a change, NA-S247N, that may slightly reduce susceptibility to the neuraminidase inhibitor oseltamivir in laboratory tests. NA-S247N has been detected sporadically in seasonal influenza viruses and has rarely been found in A(H5N1) viruses. Historically, two H5N1 viruses with the NA-S247N change have been tested for susceptibility to oseltamivir: an A(H5N1) virus collected from a chicken in Laos in 2008 (A/chicken/Laos/13/2008; PMID: 20016036) and a clade 2.3.4.4b H5N1 virus collected from a dolphin in Florida in 2022 (A/dolphin/Florida/2022; PMID: 37494978 and PMID: 38637646). These laboratory studies found either mildly reduced or reduced inhibition by oseltamivir, with results well below what has been reported for oseltamivir resistance of other influenza viruses. It is important to note that this change is not spreading in H5 viruses. Additionally, this change is not expected to have an impact on the ability of influenza viruses to replicate or spread more easily. While NA-S247N may slightly reduce antiviral susceptibility in laboratory testing, that is NOT the same as resistance. Results of laboratory studies demonstrating mildly reduced or reduced inhibition by oseltamivir may not indicate reduced effectiveness of antiviral treatment of a patient with H5N1 virus infection. NA-S247N is unlikely to have a meaningful impact on the clinical benefit of oseltamivir, which is the currently recommended antiviral for treatment for H5 bird flu. CDC continues to recommend oseltamivir for treatment of patients with H5N1 and for post-exposure prophylaxis of close contacts of confirmed H5N1 patients and those with higher risk exposures to animals infected with H5N1 viruses.
Due to low viral RNA concentrations in clinical specimens from these three cases and unsuccessful attempts to isolate virus in culture, multiple sequencing attempts were required to generate data sufficient to meet CDC quality thresholds for posting of partial NA sequences.
CDC also identified a different change in the polymerase acidic (PA) protein of a virus collected from a recently confirmed human case of H5N1 bird flu in California (A/California/150/2024). This change, PA-I38M, is associated with decreased susceptibility to the influenza antiviral medication baloxavir marboxil and has been sporadically detected in a small number of avian influenza viruses. Baloxavir is not currently recommended for treatment or post-exposure prophylaxis of H5N1 virus infection. As indicated above, oseltamivir is the recommended antiviral treatment for H5N1 bird flu. No H5N1 patients in the U.S. have received baloxavir treatment for H5N1. There are no available data on baloxavir treatment of H5N1 patients worldwide. And the optimal dosing and duration of baloxavir for treatment or post-exposure prophylaxis of H5N1 virus infection in humans are unknown.
Influenza genetic sequence data from these and other recently confirmed cases of H5 bird flu in humans have been posted in GISAID and GenBank. Additional laboratory investigations are ongoing and planned at CDC to better understand the implications of these changes in the context of the currently spreading H5 viruses. In summary, although these particular changes have not been detected widely and are not spreading among dairy cattle or birds, these findings underscore the importance of ongoing surveillance and testing to analyze H5 viruses for any changes that could potentially impact their susceptibility to flu antiviral medications.
Surveillance Update
As noted above, CDC has so far confirmed 11 cases in Washington state and 26 cases in California.
CDC continues to support states that are monitoring people with exposure to cows, birds, or other domestic or wild animals infected, or potentially infected, with avian influenza A(H5N1) virus. To date, more than 7,300 people have been monitored as a result of their exposure to infected or potentially infected animals, and at least 380 people who have developed flu-like symptoms, including conjunctivitis, have been tested as part of this targeted, situation-specific testing. More information on monitoring can be found at Symptom Monitoring Among Persons Exposed to HPAI.
In addition, since February 25, 2024, more than 60,000 specimens have been tested for avian influenza A(H5) virus or other novel influenza viruses at public health labs. One of the specimens, collected as a part of routine surveillance, was identified as presumptive positive for avian influenza A(H5) virus and was confirmed as H5N1 bird flu positive by CDC.
CDC also continues to monitor flu surveillance data using CDC's 2024-2025 influenza surveillance strategy, especially in areas where avian influenza A(H5N1) viruses have been detected in dairy cows or other animals, for any unusual trends, including in flu-like illness, conjunctivitis, or influenza virus activity. Overall, for the most recent week of data, CDC flu surveillance systems show no indicators of unusual flu activity in people.
CDC identified a change in sequence NA-S247N from 3 human specimens of H5 bird flu in poultry workers. This change has been previously associated with a slight reduction in antiviral susceptibility of influenza viruses to neuraminidase inhibitors (e.g., Tamiflu). Slightly reduced susceptibility is NOT the same as resistance. This change is unlikely to have meaningful impact on the clinical benefit of oseltamivir, which is recommended antiviral treatment of H5 bird flu. More here: bit.ly/4fxtSya
H5 bird flu is widespread in wild birds worldwide and is causing outbreaks in poultry and U.S. dairy cows with several recent human cases in U.S. dairy and poultry workers.
While the current public health risk is low, CDC is watching the situation carefully and working with states to monitor people with animal exposures.
CDC is using its flu surveillance systems to monitor for H5 bird flu activity in people
53 Confirmed Total Reported Human Cases in the United States
-snip-
Detections in Animals
10,604 wild birds detected as of 11/19/2024 | Full Report
50 jurisdictions with bird flu in wild birds
109,668,208 poultry affected as of 11/21/2024 | Full Report
49 states with outbreaks in poultry
612 dairy herds affected as of 11/21/2024 | Full Report
15 states with outbreaks in dairy cows
These data will be updated daily, Monday through Friday, after 4 p.m. to reflect any new data.
Cumulative data on wild birds have been collected since January 20, 2022. Cumulative data on poultry have been collected since February 8, 2022. Cumulative data on humans in the U.S. have been collected since April 28, 2022. Cumulative data on dairy cattle have been collected since March 25, 2024.
How CDC is monitoring influenza data among people to better understand the current avian influenza A (H5N1) situation
Weekly Snapshot for Week Ending November 16, 2024 AT A GLANCE
Note: Due to the Thanksgiving holiday, the next update will be posted on December 2, 2024.
CDC influenza (flu) surveillance systems show no indicators of unusual influenza activity in people, including avian influenza A(H5N1).
This page provides information on how CDC systems that monitor national, state, and local level influenza data are being used during the current avian influenza A(H5N1) situation.
Excerpts:
Monitoring for Novel Influenza A virus infections among people, including Influenza A (H5)
Rapid detection and reporting of human infections with novel influenza A viruses, including influenza A(H5), is important to facilitate prompt awareness and an effective public health response. For confirmed cases, the reporting jurisdiction completes a case report form, which is submitted to CDC. The information includes patient demographics, symptoms, the clinical course of illness, and exposure history. The reporting jurisdiction for influenza A(H5) cases reported in 2024 are summarized below.
Public health laboratories use CDC's diagnostic tools to detect both seasonal influenza viruses and novel influenza A viruses including influenza A(H5). These diagnostic tools are used at more than 100 public health laboratories in all 50 U.S. states. The results of tests performed by these public health laboratories nationwide are summarized below.
Region 10 - Seattle
Alaska, Idaho, Oregon, and Washington
*This graph reflects the number of specimens tested and the number determined to be positive for influenza viruses at the public health lab (specimens tested is not the same as cases). It does not reflect specimens tested only at CDC and could include more than one specimen tested per person. Specimens tested as part of routine influenza surveillance as well as those tested as part of targeted testing for people exposed to influenza A(H5) are included.
Region 9 - San Francisco
Arizona, California, Hawaii, Nevada,
American Samoa, Commonwealth of the
Northern Mariana Islands, Federated States
of Micronesia, Guam, Marshall Islands, and
Republic of Palau
H5 Bird Flu: Current Situation
NOVEMBER 21, 2024 --Continued
Monitoring for Avian Influenza A(H5) Virus In Wastewater
Wastewater surveillance may complement other existing human influenza surveillance systems to monitor influenza. Data on wastewater testing for influenza A viruses can be found through CDC's National Wastewater Surveillance System (NWSS). In addition to influenza A virus data, CDC receives weekly avian influenza A(H5) virus data from an academic partner (approximately 150 sites) and some state health departments. In each site, wastewater sampling and testing occurs one or more times during the week....
This interactive map shows current site-level data for avian influenza A(H5) viral RNA detections in wastewater. Each dot on the map represents a wastewater sampling site. For each site, results are reported as "H5 Detection" when any of the samples were positive during the week reported. When avian influenza A(H5) virus is not detected in any of the samples, then the site is classified as "No Detection." All data are preliminary and may change as more reports are received. Data will be updated on this site every Friday, based on data submitted to CDC by the end of the day on the previous Wednesday.
H5 Bird Flu: Current Situation
Update December 2, 2024 WHAT TO KNOW
H5 bird flu is widespread in wild birds worldwide and is causing outbreaks in poultry and U.S. dairy cows with several recent human cases in U.S. dairy and poultry workers.
While the current public health risk is low, CDC is watching the situation carefully and working with states to monitor people with animal exposures.
CDC is using its flu surveillance systems to monitor for H5 bird flu activity in people.
57 Confirmed Total Reported Human Cases in the United States
Confirmed human case summary during the 2024 outbreak, by state and exposure source:
