Is Milk Safe? Your Questions About Bird Flu and Dairy, Answered

The U.S. Department of Agriculture announced Friday that it would soon begin testing the country’s milk supply for H5N1, the virus that causes avian influenza.

Milk has been a central concern as cases of bird flu have ticked up over the past year. Researchers believe the virus has spread between cows and to farmworkers through contaminated milk. More than 700 dairy herds have been affected by the virus, and at least 58 people, mostly farm workers, have been sickened.

Here’s what we know about the virus and its potential impact on milk.

Why do officials want to test unpasteurized milk?

Health officials will now begin testing milk from large storage tanks at dairy processing facilities, which typically pool milk from many dairy farms, before it is pasteurized. Farmers and dairy processors will also have to provide milk samples if the government requests them, and provide details to help identify more cases if a sample is positive. This testing was previously voluntary.

Testing can help officials understand which farms and cows are infected, and how the virus is moving between them, said Matthew Moore, an assistant professor in the department of food science at the University of Massachusetts, Amherst. It will also help protect farm workers from exposure, according to the U.S.D.A.

The new testing strategy is focused on dairy processing facilities, but does not cover farms that directly process and sell their own raw milk. Regulations on raw milk farms can vary from state to state.

How much of the virus might be in raw milk?

When cows are infected with bird flu, the virus is shed in very high concentrations in their milk, said Dr. Meghan Davis, a veterinarian and environmental epidemiologist at the Johns Hopkins Bloomberg School of Public Health. Far more virus is found in their milk than in nasal swabs or blood, which may help explain why milk appears to be the main way the virus is spreading between cows and from cows to people, she said.