Infectious bird flu can remain in refrigerated raw milk for 5 days

Raw milk may be more dangerous than you think. Researchers just found evidence that flu viruses that end up in raw milk can infect people for almost a week.

Scientists at Stanford University conducted a study aimed at quantifying the threat of exposure to the flu through contaminated milk. They found that a particular strain of influenza A virus remained infectious after five days in refrigerated raw milk. The findings suggest that raw milk is a viable transmission route for similar influenza strains, particularly bird flu viruses that are now actively spreading among dairy cows.

Pasteurization is the simple, brief heating of foods and liquids to eliminate microbes that can cause spoilage or food poisoning. Unsurprisingly, extensive research has shown that raw or unpasteurized dairy products can spread harmful germs. A 2018 study, for example, found that raw milk and cheese products accounted for 96% of all reported foodborne illnesses attributed to dairy over a five-year period.

The emergence of H5N1, a highly pathogenic avian influenza A (HPAI) strain, in dairy cows this year has made raw milk even more of a risk. People have already found H5N1 in commercially sold raw dairy products. And some animals, particularly cats living on farms, are suspected of contracting H5N1 by drinking raw milk. But researchers at Stanford University say theirs is the first research to examine the persistence of influenza in raw milk under conditions more realistic to people.

The researchers seeded raw milk samples with an H1N1 strain of influenza A. They used an initial dose of the virus similar to the doses seen in contaminated commercial brand dairy products (however, thanks to pasteurization, no infectious virus was found in these products). They then kept the samples refrigerated at a typical temperature and tracked how long it took for viable virus levels to decline before it could no longer infect someone. They also tested how pasteurization would affect the viability of the virus.

As with other research, they found that pasteurization completely eliminated the presence of any infectious influenza virus. But it took up to five days for the raw milk samples to become non-infectious.

“Overall, our study demonstrates that influenza viruses remain infectious in raw milk, where they could pose a significant risk to human health,” the researchers wrote in their paper. published this month in the magazine Environmental science and technology letters.

The study analyzed a strain of influenza A other than H5N1. But other studies have shown that infectivity of both strains seems to break down at about the same rate in milk, and that influenza A viruses generally don’t differ much from each other in that regard. Therefore, H1N1 is likely to be a good substitute for H5N1.

From beginning of decemberThere have been H5N1 outbreaks among dairy cows in 16 states this year, although only California and Nevada reported cases last month. In the United States, 60 human cases of H5N1 have been documented, most related to contact with infected cows or poultry.

So far, human cases have generally been mild and the virus is not thought to have yet adapted to spread easily between people.

But more serious cases of H5N1 have also been reported. And the longer these strains are allowed to spread among cows and other mammals like us, the greater the risk that a nightmarish version of H5N1 will emerge and trigger a widespread epidemic, a risk that is only amplified by the continued popularity of raw milk. About 4% of Americans are designed to consume raw dairy products at least once a year, and 1% consume them regularly.

“This work highlights the potential risk of transmission of avian influenza through consumption of raw milk and the importance of milk pasteurization,” said lead researcher Alexandria Boehm in a statement. statement from the university.

Unfortunately, the same people who love raw dairy products are also likely to ignore any warnings about them. Raw milk sales have only skyrocketed since the emergence of the H5N1 virus this year, even in the face of remember linked to bird flu. And many raw milk supporters continue to spread misinformation about its supposed benefits over pasteurized milk, such as that it improves people’s immunity.