Flu virus can remain infectious in refrigerated raw milk for 5 days: Study

Influenza or flu virus can remain infectious in refrigerated raw milk for up to five days, scientists have warned.

The new Stanford University study comes at a time when outbreaks of bird flu in dairy cattle have raised concerns about the potential for a new pandemic.

“This work highlights the potential risk of avian influenza transmission through consumption of raw milk and the importance of milk pasteurisation,” said study senior author Alexandria Boehm from the Stanford Doerr School of Sustainability and the Stanford School of Engineering.

Proponents of raw milk claim that it leaves more beneficial nutrients, enzymes, and probiotics than in pasteurised milk, and can boost immune and gastrointestinal health.

The US Food and Drug Administration (FDA) has tied raw milk to over 200 outbreaks of illnesses, and warns that germs, such E. coli and Salmonella, in raw milk present “serious” health risks, especially for children, the elderly, pregnant women, and people with weakened immune systems.

The study, published in the journal Environmental Science and Technology Letters, explored the persistence of a strain of human influenza virus in raw cow’s milk at typical refrigeration temperatures.

The flu virus, called H1N1 PR8, survived and remained infectious in the milk for up to five days.

“The persistence of infectious influenza virus in raw milk for days raises concerns about potential transmission pathways,” said study co-lead author Mengyang Zhang, a postdoctoral scholar in civil and environmental engineering. “The virus could contaminate surfaces and other environmental materials within dairy facilities, posing risks to animals and humans.”

Notably, the researchers found that flu virus RNA – molecules that carry genetic information but are not considered a health risk – remained detectable in the raw milk for at least 57 days.

By comparison, pasteurisation completely destroyed infectious influenza in the milk and reduced the amount of viral RNA by almost 90 per cent, but didn’t eliminate the RNA entirely.

The findings underscore the importance of improving monitoring systems, particularly as bird flu continues to spread among livestock, according to the study’s authors.