April 29, 2024 -- The virus that causes bird flu is effectively inactivated through the process of heating milk known as pasteurization, the FDA confirmed.
Concerns arose recently when dairy cattle tested positive for H5N1 avian influenza, as did a farm worker. Officials have said the human infection likely stemmed from close contact with infected cows. The situation prompted FDA officials to test samples of retail milk.
These latest results come from further laboratory tests of pasteurized milk that initially indicated the samples contained inactive fragments of bird flu virus. Scientists widely expected these subsequent findings.
“This additional testing did not detect any live, infectious virus. These results reaffirm our assessment that the commercial milk supply is safe,” the FDA said in a news release late Friday, adding that the results are “preliminary.”
Testing of several samples of powdered infant formula and powdered milk products marketed as toddler formula tested entirely negative, “indicating no detection of viral fragments or virus in powdered formula products,” the FDA news release also stated.
It’s unclear how widespread the virus is among cattle in the United States. The U.S. Department of Agriculture currently lists 33 positive test results among dairy cattle, dating back to March 25 results obtained from Texas livestock. The cows from those 33 positive test results were living in six states in addition to Texas: Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, and South Dakota.
Among the pasteurized milk sampled by the FDA, 1 in 5 specimens tested positive for containing fragments of genetic material constituting inactive bits of bird flu virus, the agency reported. The FDA says further testing is ongoing of 297 samples of retail dairy products from 38 states.
In recent years, bird flu has been detected in an increasing variety of animals. The virus is already widespread among wild birds and sporadically infects commercial and backyard chicken flocks. Occasional human infections have been reported worldwide, usually due to close contact with infected birds.
Like other viruses, H5N1 is known to evolve over time. Federal officials recently published data from U.S. infections for the science community to study. University of Arizona evolutionary biologist Michael Worobey, PhD, announced on X (formerly Twitter) on Sunday that he and his colleagues had analyzed the newly released genetic data from 202 cows, nine cats, 18 chickens, one skunk, one raccoon, three grackle birds, two blackbirds, one Canada goose, one peregrine falcon, and one goose.
The Reuters news agency reported that Worobey said genetic differences between the infected cattle worker and the animal samples indicate that "this was a very longstanding, widespread epidemic.”