In a groundbreaking study researchers at Stanford University have discovered that raw milk can harbor infectious flu viruses including avian influenza for several days under standard refrigeration conditions. The findings have raised serious concerns about the potential spread of bird flu through unpasteurized dairy products, prompting experts to stress the importance of pasteurization in safeguarding public health.
The study focused on the H1N1 virus, a subtype of influenza A often used as a research surrogate for the highly pathogenic avian influenza (HPAI) H5N1 virus. Researchers infected raw milk with H1N1 and stored it at 4°C (about 39°F), the typical temperature of household refrigerators.
The results were alarming while the virus showed a 99% reduction in infectivity within 2.3 days, a small fraction of infectious particles persisted for up to five days. This timeline overlaps with raw milk’s shelf life, which is usually five to seven days, suggesting that contaminated milk could potentially infect consumers.
Thankfully, pasteurization heating milk to 63°C (145°F) for 30 minutes was found to completely inactivate the virus, eliminating the threat.
“This work highlights the potential risk of avian influenza transmission through the consumption of raw milk and underscores the critical role of pasteurization in protecting public health,” said Alexandria Boehm, lead researcher and environmental engineer at Stanford.
Bird Flu’s Leap to Dairy Farms
The study comes amid a historic development: the H5N1 bird flu virus has jumped from poultry to dairy cows in the United States for the first time. Hundreds of dairy farms have reported infections, and raw milk from infected cows has been recalled in California due to contamination concerns.
Public health officials have confirmed that H5N1 can infiltrate cows’ mammary glands, posing risks to dairy farm workers handling raw milk and milking equipment. Even domesticated cats on some dairy farms have reportedly died after consuming infected raw milk.
Cultural Beliefs vs. Public Health Risks
Despite the risks, raw milk consumption remains relatively common in the U.S., with about 4% of Americans drinking it at least once a year. Cultural beliefs and misconceptions about raw milk’s supposed health benefits such as curing lactose intolerance, boosting immunity, or providing superior nutrition fuel its popularity.
However, health experts strongly dispute these claims, pointing out that scientific evidence does not support them. Instead, raw milk is known to carry a host of dangerous pathogens, including Listeria, Salmonella, Campylobacter, and E. coli.
“Drinking raw milk can have serious, even fatal, consequences,” the Stanford researchers warned.
The risk from raw milk is heightened by the ongoing spread of HPAI H5N1. While this bird flu strain has not yet evolved to transmit easily between humans, it can jump from animals to humans, raising concerns about future mutations.
So far, human cases linked to dairy farm exposure have been mild, but the fatality rate of H5N1 in human outbreaks historically sits at around 50%. The more time the virus spends in human hosts, the greater the chance of it mutating to become more transmissible.
The Stanford study emphasizes the urgent need for widespread pasteurization and stricter monitoring of raw milk production, especially amid the growing threat of avian influenza. Public health officials are urging consumers to avoid raw milk and opt for pasteurized alternatives to protect themselves and their families.
“With bird flu spreading to new species, the risks are too great to ignore,” Boehm said.
As the flu virus adapts and evolves, safeguarding public health requires vigilance, scientific innovation, and adherence to proven safety measures like milk pasteurization
