Study Highlights Bird Flu Risks in Raw Milk Cheese

Health authorities have long cautioned against drinking raw milk due to its potential to harbor pathogens, including the bird flu virus. However, the safety of cheeses made from raw milk has remained less clear—until now.  

A preprint study conducted by researchers at Cornell University revealed that the bird flu virus can remain active in raw milk cheeses for months, raising concerns about potential public health risks. In the United States, cheeses made with raw, unpasteurized milk must be aged for 60 days before being sold, under the assumption that this process reduces the risk of dangerous pathogens. However, the study suggests that this aging period may not be sufficient to neutralize the H5N1 bird flu virus.  

While no cases of bird flu have been linked to raw milk cheese consumption in the U.S., public health experts are keeping a close watch on developments surrounding the virus.  

“The great news is that there have been no raw milk cheeses available in the marketplace to date that have been found to have infectious virus,” Nicole Martin, PhD, co-author of the study and assistant research professor in dairy foods microbiology at Cornell University, said in an email.  

The Centers for Disease Control and Prevention (CDC) advise consumers to reduce their risk of bird flu by avoiding contact with infected animals and refraining from consuming raw milk or products made from raw milk, particularly if sourced from infected cows.  

Raw Cheese Safety: Exploring the Risks  

According to experts, most raw milk cheeses should be safe for consumption after the mandated 60-day aging period. This process has historically been shown to deactivate bacterial pathogens in cheese. Keith Poulsen, DVM, PhD, clinical associate professor of medical sciences at the University of Wisconsin-Madison School of Veterinary Medicine, noted that aged raw cheese is generally safer compared to unaged raw cheese.  

“We have a lot of history and data to back that up,” Poulsen said in an email. “Unfortunately, the data from Cornell suggests that if raw milk cheeses were made on an affected farm, they would not be recommended for consumption.”  

The study’s findings point to potential reasons why the bird flu virus survived the aging process. Researchers believe the cheese’s fat and protein content, along with low aging temperatures, may contribute to the virus’s stability. Other viruses affecting cows, though not humans, may also withstand the aging process but have not been studied because they pose no widespread risk to human health.  

David J. Topham, MS, PhD, microbiology professor at the University of Rochester Translational Immunology and Infectious Disease Institute, added that the H5N1 bird flu virus likely does not have unique properties granting it the ability to endure the aging process.  

Should You Avoid Raw Cheese?  

Consumers may not need to stop eating raw cheese despite the study’s findings. Poulsen explained that most aged raw milk cheese producers operate smaller, niche artisanal cheese-making operations, which are likely at lower risk for bird flu contamination due to factors such as closed herds and limited interstate animal transport.  

For those who wish to avoid raw milk cheeses as a precaution, checking ingredient labels for “unpasteurized milk” is one option. However, the Food and Drug Administration (FDA) does not require producers to label whether cheeses were made from unpasteurized milk, which may necessitate contacting manufacturers directly to confirm processing details.  

Ultimately, the decision to avoid raw milk cheese depends on personal comfort levels. “Everybody needs to make their own decisions about how important it is to them to have these things, or maybe take a break, or adopt a wait-and-see attitude,” Topham explained.  

He added that, hypothetically, a person would likely need to eat a large quantity of contaminated cheese to be at risk of bird flu.  

The study raises important questions about the safety protocols for raw milk products, particularly amid growing concerns about zoonotic diseases such as bird flu. Although the risk remains minor for most consumers, further scientific investigations will be critical in determining whether additional measures are needed to protect public health.