The early results suggest that pasteurization is killing the H5N1 virus in milk, something that regulators were not certain of.
Federal regulators on Friday said that they had not yet discovered live bird flu virus in the first batch of retail milk samples they tested, a reassuring indication that the milk on store shelves remains safe despite an outbreak of the virus among diary cows.
In an online update, the Food and Drug Administration said an initial set of tests looking for live virus, not just genetic fragments, suggested that the pasteurization process was effectively neutralizing the pathogen.
“These results reaffirm our assessment that the commercial milk supply is safe,” the F.D.A. wrote in the update, adding that the testing efforts were ongoing.
Officials also tested infant and toddler formula, which incorporate powdered dairy, and did not find the virus, the agency wrote.
The F.D.A. embarked on a national survey of milk samples shortly after an outbreak of the bird flu virus, called H5N1, was discovered among dairy cows. Government scientists have been testing 297 samples of retail dairy products from 38 states, a swath of the country that covers regions far beyond the nine states known to have infected herds.
The first type of testing regulators conducted, a form of polymerase chain reaction, or PCR, is relatively speedy, but it picks up only genetic traces of the virus and does not tell researchers whether the live pathogen is present.