One in five samples of milk from grocery store shelves tested positive for the highly pathogenic avian influenza, the U.S. Food and Drug Administration (FDA) announced late April 25.
The FDA has refused to disclose how many samples it tested and from which stores the samples came, and a Freedom of Information Act request for the information has not yet yielded results.
Thirty-three cattle herds across eight states—Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota, and Texas—have tested positive for avian influenza, commonly known as the bird flu, according to the U.S. Department of Agriculture. Poultry in Minnesota and a person in Texas have also become infected with the same genotype of the H5N1 avian influenza strain found in cattle.
Authorities have stressed that positive results from qPCR testing do not mean the pasteurized milk contains intact virus, because the testing can return positive based on fragments of residual virus.
“Additional testing is required to determine whether intact pathogen is still present and if it remains infectious, which would help inform a determination of whether there is any risk of illness associated with consuming the product,” the FDA said.
Testing includes injecting eggs with samples that tested positive and seeing whether any active virus replicates.
In another round of testing, conducted by a team from Ohio State University, 58 of 150 milk samples gathered from grocery stores across six states tested positive for bird flu.
The FDA has said it will release more details about the testing in the future. Raw milk from farms with affected cows has also tested positive for bird flu.
Officials say it’s still safe to drink milk but some outside experts, including former U.S. government official Rick Bright, have said they’re going to hold off until more information is made public about the outbreak.
The flu originated in birds but has since moved to other animals, including cattle and goats.
The person in Texas, and an individual in Colorado who became sick in 2022, are the only humans with confirmed cases of the H5N1 version in the United States.
Monitoring of people who have come into contact with animals has only covered 44 people so far, Sonja Olsen, an epidemiologist with the U.S. Centers for Disease Control and Prevention, told an Association of State and Territorial Health Officials webinar this week. Twenty-three people who showed symptoms were tested. The person in Texas, a farm worker, has been the only person to test positive so far.
