Raw milk can be more dangerous than previously thought. Researchers have recently found evidence that flu viruses that end up in raw milk can infect people for about a week.
Scientists from Stanford University conducted the study, which was aimed at estimating the threat of exposure to influenza through contaminated milk. They found that a strain of the influenza A virus was still infectious after five days in refrigerated raw milk. The findings suggest that raw milk is an effective means of transmission of the same flu strains—especially the bird flu viruses that are now circulating among dairy cows.
Pasteurization is the simple and brief heating of foods and liquids to kill bacteria that can cause spoilage or food poisoning. Surprisingly, extensive research has shown that raw, or raw, dairy products can spread harmful bacteria. A 2018 study, for example, found that raw milk and cheese products accounted for 96% of all reported foodborne illnesses traced back to milk over a five-year period.
The emergence of H5N1, a strain of avian influenza A (HPAI), which is causing more disease in dairy cattle this year has made raw milk even more of a gamble. People are already getting H5N1 from sold raw milk products. And some animals, especially farm cats, are suspected to have contracted H5N1 by drinking raw milk. But researchers at Stanford University say their first study is to test the persistence of influenza in raw milk under real-world conditions in humans.
The researchers inoculated samples of raw milk with H1N1 type of influenza A. They used an initial dose of the virus similar to the doses seen in contaminated store milk products (thanks to pasteurization, however, no infectious virus is found in these products). They then kept the samples in a refrigerator at room temperature and tracked how long it took for the levels of the live virus to drop before it could no longer infect a person. They also tested how pasteurization could affect the viability of the virus.
Like other studies, they found that pasteurization completely eliminated the presence of any infectious influenza virus. But it took five days for the raw milk samples to become non-contagious.
“Overall, our study shows that influenza viruses are often transmitted from raw milk, where they may pose a significant risk to human health,” the researchers wrote in their paper, published this month in the journal. Books on Environmental Science and Technology.
The study looked at a different strain of influenza A than H5N1. But other studies have shown that both strains seem to decay at the same rate in milk, and that influenza A viruses generally don’t differ much from each other. So H1N1 is probably a good surrogate for H5N1.
As of early December, outbreaks of H5N1 among dairy cattle have occurred in 16 states this year, although only California and Nevada reported cases last month. In the US, 60 human cases of H5N1 have been documented, most of which have been linked to contact with infected cattle or poultry.
So far, human cases have generally been mild, and the virus is not believed to have adapted to spread easily between people yet.
But there have been more serious cases of H5N1 reported as well. And the longer these strains are allowed to spread among cows and other mammals like us, the more likely a nightmare version of H5N1 will emerge and cause a widespread pandemic—a risk only amplified by the continued popularity of raw milk. About 4% of Americans are thought to consume raw dairy products at least once a year, and 1% consume them regularly.
“This work highlights the potential risk of bird flu transmission through the use of raw milk and the importance of milk pasteurization,” said senior researcher Alexandria Boehm in a statement from the university.
Unfortunately, the very people who love raw milk products may also ignore any warning about them. Sales of raw milk have soared since the H5N1 outbreak this year, even with bird flu-related recalls. And many fans of raw milk continue to spread misinformation about its supposed advantages over unpasteurized milk, such as improving people’s immunity.
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