Situation Updates:
August 16 – The Centers for Disease Control and Prevention (CDC) continues to respond to the public health challenge posed by the outbreak of avian influenza A(H5N1) in dairy cattle, poultry, and other livestock in the United States. CDC is working with the U.S. Department of Agriculture (USDA), the U.S. Food and Drug Administration (FDA), the Administration for Strategic Preparedness and Response (ASPR), state health officials, veterinary health agencies, and other partners adopting a “One Health” approach. Since April 2024, 13 human cases of avian influenza A(H5) virus have been reported in the United States. Four of these cases were associated with exposure to sick dairy cattle, and nine were associated with exposure to poultry infected with avian influenza A(H5N1). Based on the information available at this time, CDC’s current assessment is that the immediate risk to the public from avian influenza H5 remains low.
In the field of animal health, the U.S. Department of Agriculture (USDA) reported that 191 dairy cattle in 13 U.S. states have been confirmed to have avian influenza A(H5N1) virus, with the number of infected herds continuing to rise. The USDA reported that since April 2024, A(H5) virus has been detected in 35 commercial herds and 21 rearing herds, bringing the total number of affected birds to 18.68 million.
Update Activities:
Below are highlights of CDC's recent activities as part of its ongoing and previously reported efforts:
Update Serology:
CDC continues to work with Michigan and Colorado to conduct studies of the prevalence of avian influenza A(H5N1) antibodies among dairy farm workers who may have been exposed to infected cows. Samples from both states will be tested at CDC for neutralizing antibodies to these viruses, as evidence of prior infection. Preliminary results from the Michigan-led study, released in the July 19 CDC Avian Influenza A(H5N1) Response Update, showed no specific antibodies to avian influenza A(H5N1) viruses in any of the blood samples collected in June 2024 from 35 Michigan dairy farm workers who had confirmed HPAI A(H5N1) infections. Michigan has since completed enrollment of additional farms in the state for Phase 2 of the study. CDC is working with both states to interpret and share the results of these studies as they become available.
Update Laboratory:
Antigen test of viruses isolated from five of the nine human cases in Colorado poultry workers showed that the viruses remained similar to two candidate vaccine viruses (CVVs) that CDC has developed and are available to manufacturers for vaccine production. Virus recovery from the remaining four Colorado cases was not possible, and therefore an antigen test was not conducted. Tests also showed that the viruses were the same of previous subtype 2.3.4.4b viruses isolated from dairy farm workers. Results of antiviral susceptibility testing of the viruses are pending.
CDC also continues to hold meetings with commercial laboratories to discuss licensing agreements for H5 tests and to consider developing commercial tests. CDC’s Office of Technology Transfer and Influenza Division are actively pursuing licensing agreements with several companies, several of which have been completed.
Update communication with individuals and communities most at risk of infection:
CDC continues to support outreach to farmworkers. This includes targeting outreach to farmworkers in affected counties through Facebook and Instagram platforms and digital audio and video ads. CDC also airs ads on local radio stations about 30 times a week to reach people who may not be on social media. These resources provide information in English and Spanish about the potential risks of avian influenza A(H5N1) infection, recommended preventive measures, symptoms to watch for, and what to do if symptoms develop.
Overview:
- On July 19, 2024, the Colorado Department of Public Health and Environment and the U.S. Centers for Disease Control and Prevention confirmed six human cases of H5N1 avian influenza among poultry workers associated with infected poultry at a commercial egg production facility in Weld County.
- The infected poultry workers experienced mild symptoms, and all received antiviral medications and recovered.
- This brings the total number of reported cases across the United States to ten, including previously reported human cases: Texas (1), Michigan (2), and Colorado (1).
- Of all human cases to date, four are associated with exposure to infected dairy cows, while six are associated with infected poultry.
- Of the 160 people working at the affected poultry farm, 60 have developed symptoms, and six have been confirmed to have the virus. The remaining 54 tested negative for H5N1 at the Colorado State Health Laboratory, and some have been diagnosed with other respiratory illnesses. Only symptomatic workers have been tested.
- The Centers for Disease Control and Prevention has sequenced the genome of the influenza virus from the most recent cluster of cases in Colorado, confirming that the virus is A(H5N1) lineage 2.3.4.4b. Analysis of one of the sequences indicated:
- The genetic makeup of the virus is B3.13 lineage 2.3.4.4b HPAI A(H5N1), with each gene segment closely related to viruses detected in recent poultry outbreaks and infected dairy cattle herds available from the U.S. Department of Agriculture.
- Among the human virus sequences, A/Colorado/109/2024 is most similar to the genome of the previously reported human case in Michigan.
- The sequence is essentially genetically conserved and lacks changes that would make the virus more adapted to infect or spread among humans.
- There are no changes in the virus that suggest the risk to human health has increased.
Initial investigation results into H5N1 outbreak in Michigan:
- The U.S. Centers for Disease Control and Prevention analyzed 35 blood samples collected from individuals exposed to dairy cattle infected with HPAI A(H5N1) 2.3.4.4b viruses causing animal outbreaks in the United States.
- The study participants were from multiple counties and had different roles on affected farms, but most worked directly with sick cows, and fewer than half reported using personal protective equipment (such as masks or goggles).
- These samples were tested for antibodies to avian influenza A(H5N1) 2.3.4.4b and a seasonal influenza virus (major virus) to measure antibodies.
- None of the 35 individuals tested had neutralizing antibodies (a sign of previous infection) specific to avian influenza A(H5N1), while several had neutralizing antibodies to seasonal influenza (which would be expected given the recent flu season and the vaccine).
Risk Assessment
Anxiety level:
There are no changes to previous assessments and this event continues to be of low concern at the local, regional, and global levels, but of higher concern among individuals with occupational or recreational exposure to infected animals and contaminated environments.
Regarding the latest information provided by the U.S. Centers for Disease Control and Prevention and the Colorado Department of Public Health and Environment:
- The number of human cases of H5N1 in Colorado may continue to increase; however, obtaining more data on the genome sequences of the remaining five infected individuals is important to fully understand any evolutionary changes in the virus.
- More information is needed to better understand the chains of transmission within the current outbreaks. Genome sequencing shows that at least one of the human cases in Colorado is closely linked to the outbreak in dairy cattle while workers were exposed to infected poultry.
- Despite exposure, the absence of antibodies to avian influenza A(H5N1) virus suggests that individuals working in contaminated environments have not been previously infected with avian influenza virus.
- These data are consistent with previous existing reviews and show that the prevalence of HPAI A(H5N1) antibodies even among known exposed workers is low, and importantly, to date there is no evidence of asymptomatic spread among humans exposed to infected cattle.
CDC Activities:
- Strengthening health surveillance: Health surveillance efforts should be strengthened on farms and in areas where infected animals are present to ensure early detection of cases.
- Providing vaccines and medications: Providing vaccines and antiviral medications to workers in affected areas to protect them and reduce the risk of virus transmission.
- Public awareness: Strengthening public awareness on how to handle infected birds and animals and take necessary preventive measures.
- Conducting numerous calls to state and local health departments to increase preparedness.
- Taking measures to improve the availability of personal protective equipment for farm workers.
- Updating interim recommendations for worker protection to include those working with dairy cows.
- Conducting numerous calls to groups representing farm workers.
- Launching a targeted paid digital awareness campaign in affected counties to reach farm workers with information on bird flu prevention and what to do if symptoms appear.
CDC Recommendations:
- The CDC recommends the following:
- Avoid exposure to sick or dead animals: People should avoid exposure to sick or dead animals, including wild birds, poultry, other domestic birds, and other wild or domestic animals (including cattle) whenever possible.
- Avoid exposure to animal waste and contaminated materials: People should also avoid exposure to animal waste, bedding (straw or similar materials), unpasteurized (“raw”) milk, or materials that have been in contact with or been in close contact with birds or other animals suspected or confirmed to be infected with avian influenza A(H5N1) virus whenever possible.
- Avoid drinking unpasteurized milk: Be careful not to drink unpasteurized milk. Pasteurization kills avian influenza A(H5N1) viruses, and pasteurized milk is safe to drink.
- Take precautions for people who have contact with infected animals: People whose work requires contact with infected or potentially infected animals should be aware of the risks of exposure to avian influenza viruses and should take precautions. People should also wear appropriate and recommended personal protective equipment when exposed to an infected or potentially infected animal.
- Interim Recommendations for Prevention and Surveillance: CDC has interim recommendations for prevention, surveillance, and public health investigations related to avian influenza A(H5N1) virus infections in humans.
Following these recommendations is essential to reducing the risk of infection and to reducing overall public health risks. In addition to reducing contact between infected animals and humans, containing outbreaks among animals is also important, highlighting the importance of USDA efforts.
WHO recommendations for risk management:
- The diversity of zoonotic influenza viruses requires increased surveillance in both animals and humans, as well as comprehensive screening of each zoonotic infection, and pandemic planning. To prevent viral mutations that could make human-to-human transmission easier, WHO recommends that poultry workers receive seasonal influenza vaccination.
- Global surveillance to detect virological, epidemiological and clinical changes associated with the spread of influenza viruses that may affect human and animal health, collaboration between the animal and human health sectors, and systematic follow-up of suspected human cases.
- When traveling to countries known to have animal influenza outbreaks, avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered, or touching any surface contaminated with animal waste. Travelers should also wash their hands frequently with soap and water, and the community at large should follow good food safety and hygiene practices.
- All laboratory-confirmed human infections caused by a new subtype of influenza virus must be reported under the International Health Regulations (IHR, 2005).
- WHO does not recommend special screening of travelers at points of entry or restrictions in relation to the current status of influenza viruses at the human-animal interface.
References:
- Centers for Disease Control and Prevention (CDC)
- World Health Organization (WHO)