WASHINGTON — Testing conducted by the Food and Drug Administration on pasteurized commercially purchased milk has found genetic evidence of the H5N1 bird flu virus, the agency confirmed Tuesday. But the testing, done by polymerase chain reaction, or PCR, cannot distinguish between live virus or fragments of viruses that could have been killed by the pasteurization process.
The agency said it has been trying to see if it could grow virus from milk found to contain evidence of H5N1, which is the gold standard test to see if there is viable virus in a product. The lengthy statement the agency released does not explicitly say FDA laboratories were unable to find live virus in the milk samples, but it does state that its belief that commercial, pasteurized milk is safe to consume has not been altered by these findings.
“To date, we have seen nothing that would change our assessment that the commercial milk supply is safe,” the statement said.
The document was long on assurances but short on details of what has been undertaken or found. It does not specify how many commercial samples were taken or in how many markets, nor does it indicate what percentage of the samples were PCR-positive for H5N1. The statement did not indicate if the testing suggested the amounts of viral genetic material in the milk were low or high.
The FDA, which has been dodging questions for some time about the work it is doing to assess the safety of the milk supply, said it did the commercial survey as part of its efforts to assess the federal-state milk safety system in the context of the current outbreak of H5N1 bird flu in dairy cows in at least eight states across the country. As of Monday, 33 outbreaks in herds have been confirmed.
“Some of the samples collected have indicated the presence of [H5N1] using quantitative polymerase chain reaction (qPCR) testing,” the FDA wrote in a statement.
The FDA reiterated Tuesday that it believes the pasteurization process is “very likely” to inactivate H5N1, though the agency acknowledged that no studies have been done testing the impact of pasteurization on H5N1 viruses.
The virus, which has been causing outbreaks around the world for more than a quarter century, had previously not been seen to infect cows.
“Data from previous studies that serve as the underpinnings of the FDA’s current milk supply safety assessment show that pasteurization is very likely to effectively inactivate heat-sensitive viruses, like H5N1, in milk from cows and other species,” the FDA wrote.
The FDA emphasized Tuesday that testing of commercially available milk is ongoing, and this includes efforts to discern any potential differences between different dairy products, such as cream and whole milk.
This is a developing story and it will be updated.