Why You Can Trust CNET FDA Update on Bird Flu Traces in Milk: What to Know About Pasteurized and Raw Milk
One in 5 milk samples across the US contained fragments of bird flu, the FDA says, but additional testing showed it's non-infectious.
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Fragments of the virus that causes bird flu, H5N1, were found in roughly one in five pasteurized milk samples across the US, the US Food and Drug Administration announced Thursday. A day later, the agency posted an update with good news, confirming that additional testing of the samples didn't turn up active or infectious virus, which is what experts have said would be the case since pasteurization is expected to kill or inactivate bird flu virus, as it does other potentially harmful bacteria and viruses.
The FDA says the milk supply remains safe; pasteurization is a requirement for commercial milk, making up the vast majority of milk found on store shelves (though not all, depending on local laws around raw milk sales).
Still, the announcement about evidence of virus in pasteurized milk was jarring because since bird flu was first reported in US dairy cows, evidence of it had only previously been reported in unpasteurized product, which hasn't gone through the process of heating milk to get rid of viruses and bacteria like pasteurized products have. It also suggested the virus has been spreading more widely than what's been realized in cattle.
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 FDA said in the update Friday that it would continue to assess retail samples of milk products and share results when possible.
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 pasteurization and the raw milk trend in bird flu times.
What is pasteurization? Will it kill bird flu?
Pasteurization is a heating process invented in the 1860s by French chemist Louis Pasteur and has been used widely since as a means to kill harmful bacteria and pathogens that can sometimes cause serious illness. These include bacteria that cause illness like E. coli, Listeria and Salmonella, and other pathogens.
Pasteurization is also expected to kill or inactivate the virus that causes bird flu, which is why health officials continue to say there's no risk to pasteurized dairy products or the commercial milk supply.
Some dairy products may be ultrapasteurized, which is when milk is heated more quickly than typical pasteurization (a couple of seconds) at a higher temperature and then rapidly cooled down. This extends its shelf life.
Pasteurized dairy products can be organic or nonorganic. Whether you can buy or sell raw, unpasteurized milk depends on the laws in your state. In California, for example, you can buy raw milk from stores, although it has to be properly labeled with a warning stating it's unpasteurized.
Jenna Guthmiller, an immunologist, influenza researcher and assistant professor in the Department of Immunology and Microbiology at the University of Colorado, told CNET for the article's first publish that if someone were to drink milk contaminated with H5N1, it doesn't necessarily mean they would be infected. Influenza viruses are unstable outside the body, she explained, and milk "bypasses the normal process by which we get infected" with flu.
Following up after health officials first announced traces of bird flu material in pasteurized milk, Guthmiller added Wednesday that bird flu outbreaks on dairy farms "seem to be linked to each other, in that the viruses are very closely related."
"At the moment, this outbreak seems to be isolated to these very large dairy farms," Guthmiller said, noting that she wasn't aware of these larger farms selling raw milk.
Dr. Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security, said in an email Wednesday that finding bird flu virus material in pasteurized milk doesn't change the public health risk assessment.
"Pasteurization is a process that would destroy the viability of pathogens -- it's not a process that eliminates their genetic material," he said.
Adalja previously noted it's "unclear" whether there would be a live virus in unpasteurized milk or if it could infect humans by their drinking it, he explained. Influenza viruses aren't spread to humans via ingestion. But on raw milk, he added, "there are many reasons not to drink it to begin with."
Why people drink raw or unpasteurized milk
Proponents of raw or unpasteurized milk prefer it for different reasons, including its creamier texture and taste or anecdotal reports that it's easier on digestion or more nutritious.
You can't argue with someone's taste or texture preferences when it comes to food. In terms of the nutritional or health benefits of raw milk compared with unpasteurized milk, research seems to have pushed back on or debunked the majority of claims. The FDA, for example, says that raw milk isn't a cure or antidote for lactose intolerance. The agency also claims on the same information page that people are misusing the results of a study from 2007 that was on farm milk consumption, not raw milk consumption.
In an analysis of the risks versus benefits of raw milk research, Healthline reported that any small antimicrobial benefit from raw milk would be neutralized when it's refrigerated. It also reported, based on the results of a systematic review, that minor nutrient losses of water-soluble vitamins, including some B vitamins, are already low in milk generally.
"Multiple studies have shown that pasteurization does not significantly affect the nutritional quality of milk," the Centers for Disease Control and Prevention concludes. "Scientists do not have any evidence that shows a nutritional benefit from drinking raw milk."
As someone who grew up on a dairy farm, Guthmiller used to drink unpasteurized milk herself -- she gets it. When it comes to consuming raw milk, she said, "the risks certainly outweigh the pros."
"We're getting to a point with pasteurization where it looks like real milk," Guthmiller said. In terms of nutritional quality, "you really do not affect the contents of the milk" by pasteurizing it, she said, because it's done so quickly.
If you're looking for foods with proven gut-health properties, look at adding foods like kimchi, pickled vegetables, sourdough, apple cider vinegar and buttermilk.
Risks of drinking unpasteurized milk
While the FDA says that it doesn't know yet whether bird flu can transmit to people via unpasteurized or raw dairy, it's probably not a reach to assume that raw milk is a riskier choice avian-influenza-wise than commercial milk, since raw milk hasn't gone through any type of process that would inactivate viruses.
In general, drinking raw milk has health risks. In addition to what Guthmiller called "old timey" bacteria that used to be a problem back in the day, before processes like pasteurization cleaned up the food supply, unpasteurized or raw milk can expose people to serious illnesses like E. coli and listeria. While it may cause only temporary or milder illness in most people, people with weakened immune systems, older adults, those who are pregnant and very young children are especially at risk of serious health effects from drinking unpasteurized milk.
The risk is especially high in children, according to Schaeffer, who are vulnerable to severe illness. In serious cases, health effects from drinking raw milk that's been contaminated can lead to kidney failure.
Schaeffer also pushed back on claims that diseases that once were a big problem in countries like the US, like tuberculosis, are no longer an issue. That's true about tuberculosis, she said, but we also have effective treatment for it. That's not the case, she said, for some types of illness that children can get from unpasteurized milk.
"The diseases, if anything, are even stronger -- antibiotic resistant," Schaeffer said. She added that some bacteria that may be in raw milk may go undetected by farmers because they don't cause illness in cows but do in people.
While buying raw milk from a farm you know sets higher safety standards and practices "good hygiene" during milking can reduce the risk of contaminated raw milk, it won't eliminate it, according to the CDC.