A new study from Stanford University warns that the influenza virus can remain infectious in raw milk for up to five days, raising concerns about food safety and the potential risks of avian influenza transmission.
The findings, published in Environmental Science & Technology Letters, come as bird flu spreads among U.S. dairy cattle, prompting questions about its ability to jump to humans.
Raw Milk and the Risk of Viral Contamination
More than 14 million Americans consume raw milk annually, opting for its unprocessed state, which proponents claim preserves nutrients, enzymes, and probiotics. However, unpasteurized milk also carries significant health risks, as it has been linked to outbreaks of E. coli, Salmonella, and other harmful bacteria.
The Stanford study expands on these concerns, demonstrating that the H1N1 influenza virus (a common human flu strain) can survive in raw milk for days at typical refrigeration temperatures.
- Live influenza virus remained infectious in raw milk for up to five days.
- Flu virus RNA (genetic material) persisted in the milk for at least 57 days, even after pasteurization.
“The persistence of infectious influenza virus in raw milk for days raises concerns about potential transmission pathways,” said Mengyang Zhang, a postdoctoral scholar in civil and environmental engineering and co-lead author of the study.
Pasteurization Eliminates Live Influenza Virus
The good news is that pasteurization completely destroyed live influenza viruses in milk. However, it did not eliminate viral RNA entirely, which is not a health risk but could complicate environmental surveillance efforts that rely on RNA detection.
“Pasteurization significantly reduces viral RNA, but traces still linger, which has implications for food safety assessments and public health monitoring,” said co-lead author Alessandro Zulli.
Bird Flu in Dairy Cattle Sparks Pandemic Concerns
The study’s findings are particularly alarming in light of recent bird flu outbreaks in U.S. dairy cows. While avian influenza has not yet caused widespread human illness, experts warn that mutations could make it more transmissible to humans—similar to the swine flu pandemic of 2009-2010, which infected as many as 1.4 billion people worldwide.
“Bird flu has not yet proven highly dangerous to humans, but it could mutate to become so,” said study senior author Alexandria Boehm, a professor at the Stanford Doerr School of Sustainability and Stanford School of Engineering. “Our work highlights the importance of pasteurization and monitoring systems as bird flu spreads.”
Reference: Alessandro Zulli, Mengyang Zhang, Sehee Jong, Catherine Blish, Alexandria B. Boehm. Infectivity and Persistence of Influenza A Virus in Raw Milk. Environmental Science & Technology Letters, 2024.
