Influenza viruses can remain infectious in refrigerated raw milk for up to five days, according to a recent study from Stanford University. This raises concerns about the potential risks of consuming unpasteurized milk, especially as outbreaks of bird flu in livestock increase globally.

The study, led by researchers from the Stanford Doerr School of Sustainability and the Stanford School of Engineering, shows the importance of pasteurization to prevent the transmission of avian influenza and other pathogens. “This work underscores the potential risk of avian influenza transmission through raw milk consumption and the critical role of milk pasteurization,” explained senior author Alexandria Boehm.

Proponents of raw milk argue that it retains more nutrients, enzymes, and probiotics compared to pasteurized milk, which they believe benefits immune and gastrointestinal health. However, the U.S. Food and Drug Administration (FDA) strongly cautions against consuming raw milk, linking it to over 200 outbreaks of illnesses caused by bacteria such as E. coli and Salmonella. These pathogens pose significant health risks, particularly to vulnerable groups like children, the elderly, pregnant women, and individuals with weakened immune systems.

The research, published in Environmental Science and Technology Letters, examined how a strain of human influenza virus, H1N1 PR8, behaved in raw cow’s milk stored at typical refrigeration temperatures. The virus survived in the milk for up to five days and remained infectious during that period.

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

Interestingly, while pasteurization eliminated infectious influenza virus in the milk and reduced the presence of viral RNA by nearly 90 per cent, the RNA itself remained detectable for at least 57 days. Although viral RNA is not infectious, its presence signals the potential for contamination.

These findings emphasize the need for robust monitoring systems, especially as bird flu continues to spread among livestock. The researchers advocate for stricter safety measures in dairy production to minimize the risks associated with raw milk consumption.

As Dr Boehm noted, “Pasteurization remains a critical safeguard against the transmission of infectious diseases through milk products.”

Raw milk may harbour harmful bacteria such as E. coli, Salmonella, and Listeria, which pose serious health risks. To make raw milk safe for consumption, pasteurization is the most effective method. Here’s how you can do it at home:

Pour the raw milk into a clean, heavy-bottomed pot. Heat it slowly over medium heat until it reaches 161 degrees F (72 degrees C). Use a food thermometer to monitor the temperature accurately.

Once the milk reaches 161 degrees F, maintain this temperature for at least 15 seconds. This step ensures the destruction of harmful pathogens while retaining much of the milk's nutritional value.

Remove the pot from the heat and transfer the milk to a sterilized container. Place the container in an ice bath to cool it rapidly to 40 degrees F (4 degrees C) or lower.

- Store Properly:

Refrigerate the pasteurized milk immediately in a sealed container. Consume it within a week for the best quality and safety.

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