Researchers at Stanford University found flu virus can remain infectious in raw milk for as long as five days.
In a study published December 12, scientists investigated how the human flu virus H1N1 PR8 behaved in raw milk kept at refrigeration temperature. The study showed the strain survived and stayed infectious for up to five days, and molecules of flu virus RNA — which are not an infection risk — persisted for at least 57 days.
The pasteurization process, which heats milk and milk products to high temperatures, destroys infectious virus material completely and reduces levels of viral RNA by close to 90%.
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The new research comes as flu concerns in the U.S. are on the rise.
Multiple batches of raw milk tested positive for bird flu in California in November, leading to voluntary recalls.
And in December, two domestic cats died from suspected bird flu after drinking raw milk linked to the flu recalls.
Raw milk is also in the public eye thanks in part to President-elect Donald Trump’s nomination of Robert F. Kennedy, Jr. to lead the Department of Health and Human Services. Kennedy has promoted raw milk and claimed it has health benefits — a position that some health experts warn is dangerous, particularly for young children who may drink it.
While bird flu in raw milk has so far not presented a danger to humans, the Stanford researchers say their new findings show that there could be an increased risk of spreading the disease in human environments.
“The persistence of infectious influenza virus in raw milk for days raises concerns about potential transmission pathways,” said study co-lead author Mengyang Zhang in a news release. “The virus could contaminate surfaces and other environmental materials within dairy facilities, posing risks to animals and humans.”
Flu viruses in general kill some 50,000 people in the U.S. every year.
