On April 23, the FDA said remnants of the bird flu virus have been detected in samples of pasteurized milk in the U.S. The agency said the finding does not change its assessment that the commercial milk supply is safe.
While polymerase chain reaction testing found virus particles in samples of commercial milk, a positive result does not differentiate between live virus or fragments of inactive virus.
"Based on available information, pasteurization is likely to inactivate the virus, however the process is not expected to remove the presence of virus particles," the FDA said in a statement. "Therefore, some of the samples collected have indicated the presence of [highly pathogenic avian influenza] using quantitative PCR testing."
The FDA is conducting further testing to determine whether pasteurization inactivates bird flu in milk.
"To date, we have seen nothing that would change our assessment that the commercial milk supply is safe," federal regulators said, adding that results from multiple studies will be made public in the "next few days to weeks."
Officials did not specify how many samples of pasteurized milk tested positive for virus fragments or where the samples came from, which experts told The New York Times are key questions that would help indicate how widespread the outbreak in dairy cattle actually is.
In late March, the Department of Agriculture confirmed H5N1 had been detected among dairy cattle for the first time. Since then, dairy cows in eight states have tested positive for the virus. One human case in Texas is believed to be tied to the outbreaks among dairy cattle. The individual worked on a dairy farm and developed a mild case of illness.
While bird flu does not spread easily among humans, infectious disease experts have urged the federal government to ramp up testing and sequencing efforts among dairy cows to detect any potential genetic changes that could make it more adept at spreading to and among people.