Chilled raw milk contains a contagious flu virus for five days, research shows

Raw milk, praised by some as a natural and nutritious alternative to pasteurized dairy, may carry hidden dangers, according to a new study from Stanford University. The research, published December 12 Letters on Environmental Science and Technology reveals that flu or influenza virus in refrigerated raw milk can remain contagious for up to five days. The findings come at a time when bird flu outbreaks among dairy cattle have raised concerns about the potential for a new pandemic.

“This work highlights the potential risk of bird flu transmission through the consumption of raw milk and the importance of milk pasteurization,” said senior author Alexandria Boehm, Richard and Rhoda Goldman Professor of Environmental Studies at the Stanford Doerr School of Sustainability and Stanford University. School of Technology.

More than 14 million Americans consume raw milk every year. Unlike pasteurized milk, raw milk is not heated to kill potentially harmful pathogens. Proponents of raw milk claim that it contains more beneficial nutrients, enzymes and probiotics than pasteurized milk, and that it can promote immune and gastrointestinal health.

The Food and Drug Administration has linked raw milk to more than 200 disease outbreaks, and – along with the Centers for Disease Control and Prevention– warns that pathogens, such as E. coli and Salmonella, in raw milk pose ‘serious’ health risks, especially for children, the elderly, pregnant women and people with weakened immune systems.

The science behind the risk

The researchers examined the persistence of a strain of human influenza virus in raw cow’s milk at typical refrigeration temperatures. The flu virus, called H1N1 PR8, survived and remained infectious in the milk for up to five days.

“The persistence of the contagious influenza virus in raw milk for days raises concerns about possible transmission routes,” said co-lead author Mengyang Zhang, a postdoctoral researcher in civil and environmental engineering. “The virus can contaminate surfaces and other environmental materials within dairy facilities, posing risks to animals and people.”

In addition, the researchers found that flu virus RNA – molecules that contain genetic information but are not considered a health risk – remained detectable in the raw milk for at least 57 days. By comparison, pasteurization completely destroyed the infectious flu in the milk and reduced the amount of viral RNA by almost 90%, but did not completely eliminate the RNA. Although exposure to influenza virus RNA does not pose a health risk, RNA-based testing methods are often used to conduct environmental surveillance for pathogens such as influenza.

“The long-term persistence of viral RNA in both raw and pasteurized milk has implications for food safety assessments and environmental surveillance, especially since many of the techniques used in environmental surveillance detect RNA,” said co-lead author Alessandro Zulli, a postdoctoral researcher in the laboratory . civil engineering and environmental engineering.

The research grew out of an earlier project focused on human norovirus and the subfamily of viruses responsible for the COVID-19 pandemic.

Why it matters now

In the US alone, flu viruses infect more than 40 million people and kill more than 50,000 each year. These types of viruses can spread from animals to humans, as in the case of swine flu, which led to as many as 1.4 billion human infections worldwide between 2009 and 2010.

Although bird flu has not yet proven to be that dangerous to humans, it could mutate to become so. The recent detection of bird flu in cattle has raised questions about its possible transmission through milk and other dairy products.

The study’s findings underscore the importance of improving monitoring systems, especially as bird flu continues to spread among livestock, the study authors said.

The study adds previous research involving some of the same researchers who pioneered the use of wastewater for bird flu detection. That analysis found that commercial and industrial dairy waste was the primary source. By analyzing wastewater, public health officials were able to detect virus activity in nearby livestock populations.

“We never imagined that wastewater could be used to detect and respond to zoonotic pathogens circulating in the community,” Boehm said. “It has been great to see how our work in wastewater detection has developed in the United States and around the world.”