CDC A(H5N1) Bird Flu Response Update July 26, 2024

What to Know

In this week's Spotlight, we confirm three additional cases of H5 bird flu in poultry farm workers at a second poultry farm in Colorado, for a total of 13 human cases since April 2024. All three people were working to depopulate infected poultry as part of a culling at a commercial egg layer operation that had reported an outbreak of H5 bird flu among poultry. All three people have mild illness and have been offered antiviral medication.

Today's edition includes details about CDC's genetic sequence analysis of the virus obtained from the sixth human case of H5N1 bird flu that was reported in association with exposure to infected poultry at a poultry farm in Colorado on July 19th. The findings are reassuring, showing it is closely related to the first human case from Colorado and that it does not have changes in the neuraminidase associated with antiviral resistance. The sequence was uploaded to public databases so that researchers in the United States and around the world can analyze it.

Finally, we include information about Emergency Use Instructions (EUI) issued for the flu antiviral drug, oseltamivir, and describe a new MMWR Notes from the Field report.

CDC Update

July 26, 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, 13 human cases of avian influenza A(H5) infection have been reported in the United States. Four of these cases were associated with exposure to sick dairy cows and nine were associated with exposure to avian influenza A(H5N1)-infected poultry. A BThis includes three additional cases in Colorado that were confirmed by CDC this week. The three new cases were in poultry workers who were working directly with infected poultry at a commercial egg layer operation that had reported an outbreak of H5 bird flu among poultry. Similar to previous cases, all of the people have mild illness. Based on the information available at this time, CDC's current assessment is that the risk to the general public from H5 bird flu remains low. On the animal health side, USDA is reporting that 171 dairy cow herds in 13 U.S. states have confirmed cases of avian influenza A(H5N1) virus infections in dairy cows as the number of infected herds continues to grow. USDA reports that since April 2024, there have been A(H5) detections in 35 commercial flocks and 19 backyard flocks, for a total of 18.37 million birds affected.

Among other activities previously reported in past spotlights and ongoing, recent highlights of CDC's response to this include:

Colorado Investigation Update

More than 600 workers performing depopulation activities on three poultry farms have been screened for symptoms. Of these, 103 had symptoms and were tested, and nine were positive for influenza A(H5). Other respiratory viruses such as SARS-CoV-2 (the virus that causes COVID-19) were also detected among symptomatic workers. Symptom onset began within two-three days and peaked within five days after the start of depopulation. Among nine workers who tested positive for avian influenza A(H5), all reported mild symptoms (predominantly conjunctivitis) and were tested within three days of symptom onset. All cases have been provided oseltamivir and are recovering. More in-depth summaries of the investigation are in process with Colorado Department of Public Health and Environment.

Laboratory Update

CDC sequencing of the virus from the sixth human case reported from Colorado confirms the neuraminidase (the N in the subtype) is an N1 and the virus is a HPAI A(H5N1) virus from clade 2.3.4.4b. Six of the eight influenza virus gene segments (the majority of the flu genome) were successfully sequenced. The sequences are closely related to the virus sequence described last week, A/Colorado/109/2024, as well as viruses detected in recent poultry outbreaks and infected dairy cattle herds made available from USDA. The sequence maintains primarily avian genetic characteristics and lacks changes that would make the virus better adapted to infect or spread among humans.

The influenza virus sequence contains a change at PB2 M631L – which is the same marker of mammalian adaptation identified in more than 99% of dairy cow sequences and that was also identified in the first Michigan human case. The influenza virus sequence does NOT have the PB2 E627K change that was seen in the virus from the case in Texas but not subsequent human viruses. That change is known to be associated with viral adaptation to mammalian hosts and has been found before in people and other mammals, but with no evidence of onward spread among people.

Furthermore, there are no markers known to be associated with influenza antiviral resistance to neuraminidase-inhibitors found in the virus sequence from the patient's specimen. The genetic sequences for the virus from the patient (A/Colorado/134/2024) were posted to two sequence databases: GISAID (EPI_ISL_19280426) and GenBank (PQ060139). Influenza virus isolates and sequences were only successfully generated from two of the six human cases from the first poultry farm in Colorado. Overall, the genetic analysis of this HPAI A(H5N1) virus in Colorado supports CDC's conclusion that the human health risk currently remains low.

CDC also continues to meet with commercial laboratories to discuss H5 assay licensing agreements and interest in development of commercial H5 tests. CDC's Technology Transfer Office and the Influenza Division are actively pursuing establishing licensing agreements with multiple companies, and several have been completed.

Clinical Update

On July 19, 2024, CDC issued Emergency Use Instructions (EUI) for the flu antiviral drug, oseltamivir (generic for brand name drug Tamiflu^®), for treatment or post-exposure prophylaxis (PEP) of pandemic influenza A viruses and novel influenza A viruses with pandemic potential. EUI provide information about emergency use of FDA-approved medical products that differ from or go beyond the information provided in the FDA-approved labeling (package insert). CDC-issued oseltamivir EUI fact sheets for health care providers and recipients and caregivers are available on CDC's website: Emergency Use Instructions (EUI) for Oseltamivir.

Partnership and Support Update

CDC is in close contact with a CDC multidisciplinary bilingual field team deployed to support Colorado's response to ongoing poultry outbreaks. The team includes epidemiologists, veterinarians, clinicians and an industrial hygienist. Support includes accompanying Colorado health officials during daily visits to the affected farm to monitor workers for symptoms, test symptomatic persons, dispense antiviral treatment, follow-up with persons testing positive to collect additional information, and assess use of personal protective equipment.

Outreach Update

CDC continues to support strategies to maximize protection of farm workers, who are at higher risk of infection based on their exposures. This includes specific outreach to farm workers in affected counties through Meta (Facebook and Instagram), digital display, and audio (Pandora). These resources provide information in English and Spanish about potential risks of avian influenza A(H5N1) infection, recommended preventive actions, symptoms to be on the look-out for, and what to do if they develop symptoms. Since May 30, when English assets launched, Meta outreach generated more than 10.6 million impressions. Spanish Meta assets launched on June 6, and since then garnered nearly 1.7 million impressions. (Table 1)

Surveillance Update

On Friday, July 26, 2024, CDC posted updated data on its website regarding the number of confirmed human cases of H5 bird flu and the number of people who have been monitored and tested in the United States since the beginning of the current outbreaks in dairy cows and other animals in 2024. Data are provided on the number of specimens tested at public health labs since February 25, 2024, using a test that would detect H5 bird flu or other novel influenza viruses, if they were present. Targeted H5 bird flu surveillance data on people monitored, people tested, and human cases is provided since March 24, 2024, the week that the first H5 detections in dairy cows were reported. The updated data are featured on CDC's H5 bird flu current situation page as well as the monitoring for H5 in people page. On the latter page, in addition to the overall numbers of people monitored and tested, data are available broken down by exposure to dairy cows, or by exposure to birds and other animals, including poultry (non-dairy cow sources).

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) viruses. To date, more than 4,100 people have been monitored as a result of their exposure to infected or potentially infected animals, and at least 200 people who have developed flu-like symptoms have been tested as part of this targeted, situation-specific testing. Testing of exposed people who develop symptoms is happening at the state or local level, and CDC conducts confirmatory testing. Since February 25, 2024, more than 36,000 specimens have been tested at public health labs that would have detected avian influenza A(H5) or other novel influenza viruses. More information on monitoring can be found at Symptom Monitoring Among Persons Exposed to HPAI.

CDC also continues to monitor flu surveillance data using CDC's enhanced, nationwide summer 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, including avian influenza A(H5N1) viruses.

Publication Highlights

On July 25, 2024, CDC published a MMWR Notes from the Field report that describes the public health efforts in Michigan that led to the identification of two different cases of influenza A (H5N1) among dairy workers – the second and third such cases in the United States, and first with respiratory virus infection. Investigators worked with farm operators to gather lists of people potentially exposed to avian influenza A(H5N1) virus on impacted dairy and poultry farms. Those people were enrolled into symptom monitoring and offered testing for influenza if experiencing signs or symptoms of illness and provided antiviral medications. Read the report: Notes from the Field: Health Monitoring, Testing, and Case Identification Among Persons Exposed to Influenza A(H5N1) — Michigan, 2024

CDC Recommendations

As a reminder, CDC recommends that:

• People should avoid exposures to sick or dead animals, including wild birds, poultry, other domesticated birds, and other wild or domesticated animals (including cows), if possible.
• People should also avoid exposures to animal poop, bedding (litter), unpasteurized ("raw") milk, or materials that have been touched by, or close to, birds or other animals with suspected or confirmed avian influenza A(H5N1) virus, if possible.
• People should not drink raw milk. Pasteurization kills avian influenza A(H5N1) viruses, and pasteurized milk is safe to drink.
• People who have job-related contact with infected or potentially infected birds or other animals should be aware of the risk of exposure to avian influenza viruses and should take proper precautions. People should wear appropriate and recommended personal protective equipment when exposed to an infected or potentially infected animal(s). CDC has recommendations for worker protection and use of personal protective equipment (PPE).
• CDC has interim recommendations for prevention, monitoring, and public health investigations of avian influenza A(H5N1) virus infections in people.

Following these recommendations is central to reducing a person's risk and containing the overall public health risk.

In addition to limiting interactions between infected animals and people, containing the outbreak among animals also is important, which underscores the urgency of the work being done by USDA and animal health and industry partners.

This is an evolving situation, and CDC is committed to providing frequent and timely updates.