Fragments of the virus that causes bird flu, H5N1, has been found in samples of pasteurized milk, according to a Tuesday update from the US Food and Drug Administration.
Since bird flu was first reported in dairy cows herds earlier this spring, health agencies have only previously reported detecting the virus in samples of raw or unpasteurized milk, which hasn’t gone through the process of heating milk to get rid of viruses and bacteria like pasteurized products have.
Still, the agency stressed the commercial milk supply is still safe. Pasteurization is expected to inactivate bird flu virus and make it non-infectious — even if parts of its genetic material are now showing up in some milk samples — and it’s a requirement for milk entering the commercial milk supply, making up the vast majority of milk found on store shelves (though not all, depending on local laws).
“Based on available information, pasteurization is likely to inactivate the virus, however the process is not expected to remove the presence of viral particles,” the FDA said.
“Therefore, some of the samples collected have indicated the presence of HPAI using quantitative polymerase chain reaction (qPCR) testing,” the agency said in the update, referring to bird flu’s official term, highly pathogenic avian influenza, and a type of test that can detect evidence of a virus that isn’t active or infectious.
While the current public health threat to people remains low, some scientists and infectious disease experts have expressed concerns about US health agencies’ response to bird flu in farm animals and their lack of details on the information pertaining to milk samples. Virologist Angela Rasmussen, for example, said in an X thread Tuesday that the new milk findings suggest the disease may be spreading asymptomatically in cows and more broadly than previously thought and that an “apparent lack of transparency and urgency” to share relevant data may be harming the ability to respond.
The US Department of Agriculture on Wednesday issued a federal order requiring testing of cows as they move across state lines, in hopes of curbing the spread of bird flu. The New York Times reported that the USDA doesn’t require farms to test cattle for infection. Normally, milk from sick cows (whatever their illness) and milk that looks off is separated from the rest of the supply.
And what about the noncommercial milk supply, or raw milk that hasn’t been pasteurized? While people who grew up on farms or around cattle might have had unpasteurized milk for dinner, raw milk has found a growing audience: people seeking it out for wellness purposes or sometimes traveling to local farms to consume a food they feel is more natural or holistic.
About raw milk or dairy products during these bird-flu times, citing limited information on bird flu in dairy, the FDA says it doesn’t know whether bird flu viruses can be transmitted through unpasteurized products. The agency is reiterating its general stance that people should avoid consuming raw or unpasteurized milk for risks of consuming pathogens that are particularly dangerous to children, older people, people who are pregnant and people with weakened immune systems.
The experts I spoke with for this story before it was first published earlier this month essentially said, in general, influenza isn’t spread to people through eating or drinking. However, they stressed the existing health risks of unpasteurized milk, consumption and sales of which often fall outside what you’d typically see on grocery store shelves, dependent on local laws.
“In my opinion, there’s a concern with raw milk acquisitions which can become part of the food system, and people secure that milk outside of going to the grocery store,” Meg Schaeffer, an infectious disease epidemiologist and National Public Health adviser at the analytics firm SAS, told CNET when this article was first published.
Here’s what to know about unpasteurized milk, why people drink it and how we should be thinking about it in the context of bird flu in dairy cows.