Regulators have refused to disclose key details about the tested samples.
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.
In a brief 237-word update, the FDA said that initial results from a national commercial milk sampling study “show about 1 in 5 of the retail samples tested are quantitative polymerase chain reaction (qPCR)-positive for HPAI viral fragments, with a greater proportion of positive results coming from milk in areas with infected herds.”
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.
“We’ve screened them for the presence of influenza genetic material, so the viral RNA. Those that have tested positive, we have been forwarded to St. Jude Children’s Research Hospital, where they are conducting studies to see if there’s a viable virus in there. To date, none of them have been viable, but certainly they give the indication that there is viral genetic material in the region,” Dr. Andrew Bowman, an associate professor at Ohio State University, told the Bovine Veterinarian magazine.
