A recent study has revealed potential dangers in raw milk, which is often marketed as a natural and healthier alternative to pasteurized dairy. The research has found that the influenza virus can stay infectious in refrigerated raw milk for up to five days. This finding comes amid concerns over bird flu outbreaks in dairy cattle, heightening fears of a possible new pandemic. The study was conducted by Stanford University.

Alexandria Boehm, the senior author of the study and the Richard and Rhoda Goldman Professor of Environmental Studies at the Stanford Doerr School of Sustainability and the Stanford School of Engineering said, "The study says the potential risk of avian influenza transmission through the consumption of raw milk and emphasizes the critical importance of milk pasteurization."

Each year, over 14 million Americans drink raw milk. Unlike pasteurized milk, raw milk is not heated to eliminate harmful pathogens. Supporters of raw milk argue that it retains more beneficial nutrients, enzymes, and probiotics than pasteurized milk and that it can improve immune and gastrointestinal health.

The Food and Drug Administration has connected raw milk to over 200 illness outbreaks. Together with the Centers for Disease Control and Prevention, they warn that harmful bacteria like E. coli and Salmonella in raw milk can be dangerous, especially for children, the elderly, pregnant women, and people with weakened immune systems.

In their study, researchers tested how long the H1N1 PR8 flu virus could survive in raw cow's milk at regular fridge temperatures. They found it remained infectious for up to five days."The presence of infectious flu virus in raw milk for several days raises concerns about how it could spread," said Mengyang Zhang, a co-lead author of the study.

"The virus could contaminate surfaces and materials in dairy facilities, putting both animals and humans at risk."
The researchers also found that the genetic material (RNA) of the flu virus, which is not harmful by itself, stayed detectable in raw milk for up to 57 days. 

In comparison, pasteurization completely killed the infectious virus and reduced the viral RNA by nearly 90%, though some RNA remained. While the RNA doesn’t pose a health risk, it is commonly used in testing to monitor the presence of viruses like influenza.This research was built on a previous project funded by the Stanford Woods Institute, which focused on human norovirus and the viruses behind Covid-19.

In the U.S., flu viruses infect over 40 million people and cause more than 50,000 deaths each year. These viruses can spread from animals to humans, as seen with swine flu, which caused 1.4 billion infections worldwide in 2009-2010. While bird flu hasn't been very harmful to people yet, it could mutate into a more dangerous form. Recent bird flu cases in cattle have raised concerns about the virus spreading through milk and dairy products.

The study marks the need for better monitoring, especially as bird flu spreads among livestock. It also builds on earlier research by the same team, which used wastewater to detect avian influenza. This method showed that dairy waste is a major source of the virus. By analyzing wastewater, public health officials could track virus activity in cattle populations nearby.