Over 14 million Americans consume raw milk yearly, not heated like pasteurized milk, to kill harmful pathogens. Raw milk advocates argue that it retains more beneficial nutrients, enzymes, and probiotics and can help boost immune and digestive health.
However, the Food and Drug Administration (FDA) has linked raw milk to over 200 illness outbreaks. Along with the Centers for Disease Control and Prevention (CDC), the FDA warns that raw milk can carry dangerous germs, such as E. coli and Salmonella, which pose serious health risks, particularly to children, the elderly, pregnant women, and those with weakened immune systems.
Now, a new study has added a new risk to the list. The study by Stanford University reveals that influenza or flu virus can remain infectious in refrigerated raw milk for up to five days.
The findings come as outbreaks of bird flu, a different subtype of influenza virus, in dairy cattle have sparked concerns about the potential for a new pandemic. These incidents have added to the ongoing debate over the safety of consuming raw milk, as the risk of transmitting diseases from animals to humans continues to be a significant public health concern.
Study senior author Alexandria Boehm, the Richard and Rhoda Goldman Professor of Environmental Studies in the Stanford Doerr School of Sustainability and the Stanford School of Engineering, said, “This work highlights the potential risk of avian influenza transmission through consumption of raw milk and the importance of milk pasteurization.”
Researchers have studied the persistence of the H1N1 PR8 human influenza virus in raw cow’s milk at typical refrigeration temperatures. They found that the virus could survive and remain infectious for up to five days.
The persistence of infectious influenza virus in raw milk for days raises concerns about potential transmission pathways. The virus could contaminate surfaces and other materials in dairy facilities, posing risks to animals and humans.
In addition, the researchers detected flu virus RNA—genetic material that does not pose a direct health risk—in the raw milk for at least 57 days.
In comparison, pasteurization completely destroys the infectious influenza virus in the milk and reduces the amount of viral RNA by nearly 90%, although it doesn’t eliminate the RNA entirely. While RNA is not harmful, environmental surveillance often uses it to track pathogens like influenza.
The prolonged presence of viral RNA in both raw and pasteurized milk has important implications for food safety assessments and environmental surveillance.
Although bird flu has not yet proven highly dangerous to humans, it could mutate into a more harmful strain. The recent detection of bird flu in cattle has raised concerns about the virus’s possible transmission through milk and other dairy products.
The study’s findings highlight the need for improved monitoring systems, especially as bird flu continues to spread among livestock. According to the study’s authors, better tracking could help prevent outbreaks and mitigate risks to public health.
Journal Reference:
- Alessandro Zulli, Mengyang Zhang, Sehee Jong, Catherine Blish, and Alexandria B. Boehm. Infectivity and Persistence of Influenza A Virus in Raw Milk. Environmental Science & Technology. DOI: 10.1021/acs.estlett.4c00971