Avian Influenza A(H5) Outbreak | Center for Outbreak Response Innovation

Current US Outbreak

As of November 26, 2024:

Critical Epidemiological Updates

CDC has confirmed the first H5N1 case in a child living in Alameda County, CA. The case was mild, and follow-up testing was negative for H5 but positive for other common respiratory viruses. All household members of the child were symptomatic but negative for H5 at the time of testing, with some positive for the same common respiratory viruses as the child. The child did attend daycare while symptomatic prior to testing positive for H5; individuals have been notified and offered preventative testing and treatment "out of an abundance of caution.” No other information about daycare contacts is available at this time. Genetic information for the H5 strain is not yet available.
California identified that raw milk from Fresno County contained active H5N1 virus. CDPH has issued a press release and the company has elected to recall the batch. No individuals have been found ill yet as a result of the raw milk from this batch. An estimated 4% of the US population drinks raw milk once a month. People who consume raw milk may be exposed to H5N1 and have the potential to become ill. Previous animal studies have demonstrated this type of transmission among other mammals. Pasteurizing milk is the only known safe way to eliminate the risk of H5N1 in dairy products.
A mutation was observed from the Canadian teen that has the potential to confer better adaptation of the virus for humans. This mutation is a residue 226, and has the potential to dramatically increase receptor binding preference for human lungs, which can make it more transmissible to humans through the air. Canadian health experts believe that it is likely the virus acquired this new trait during the course of infection for the Canadian teen and the mutation will die out since no other contacts tested positive for H5N1, however, since the source of the infection remains unknown this is not certain.

Routine Surveillance Updates

The Centers for Disease Control and Prevention (CDC) is reporting 55 confirmed human cases of H5 in the United States as of November 25, 2024. Two of these cases have not had a known source of infection, and reported no contact with animals or raw milk.
The United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) has reported 261 new infected cattle herds across two states (UT, CA) in the last 30 days, bringing the total for the outbreak to 650 cattle herds in 15 state. This represents a slight increase compared to the previous 30 days.
CDC reports that for the duration of the outbreak, 250 tests for poultry workers and 131tests for dairy workers have been sent to CDC for H5N1 testing, resulting in a positivity rate since March 2024 of 8.4% (21/250) and 20.6% (32/140), respectively.