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New research suggests that the H5N1 bird flu virus may survive the aging process in raw milk cheese, raising concerns about potential infection risks. A study published on the bioRxiv preprint server indicates that the virus can remain infectious in raw milk cheese aged for 60 days, the minimum period required for legal sale across state lines in the U.S.
The study, led by Dr. Diego Diel of Cornell University, involved creating mini cheeses laced with the H5N1 virus at varying pH levels. Researchers then tested the cheeses by injecting samples into fertilized chicken eggs to determine the virus’s viability. The results showed that while viral levels decreased in less acidic cheeses, infectious levels persisted in cheeses with a pH of 6.6 for the full 60-day aging period. No live virus was detected in the most acidic cheese (pH 5.0).
“There is a risk of infection,” Dr. Diel told CNN, emphasizing that the risk depends on the dose of contaminated product ingested. The team had previously demonstrated that the H5N1 virus can remain infectious in refrigerated raw milk for up to eight weeks.
The findings challenge the long-held belief that the 60-day aging process effectively eliminates pathogens in raw milk cheese. “Our study demonstrates that the HPA1 H5N1 virus exhibits remarkable stability throughout the cheese-making process,” the authors wrote.
While pasteurization has been shown to inactivate the virus, the new research suggests that acidity plays a crucial role in virus survival. Dr. Seema Lakdawala of Emory University, who reviewed the findings, noted that “a much lower pH than is normal is needed to inactivate the virus.”
Despite these findings, U.S. health officials maintain that food does not present a bird flu risk. Robert F. Kennedy Jr., Secretary of the U.S. Department of Health and Human Services, stated last week that “the disease is not passed through food, so you cannot get it—as far as we know, you cannot get it from an egg or milk or meat from an infected animal.”
The FDA has also addressed the issue, posting the research findings alongside preliminary results from an ongoing sampling study of raw cheese. Of 110 cheese samples, 96 tested negative for live virus and inactive viral particles, suggesting they were likely made from uncontaminated milk. Results for 14 samples are pending.
“The FDA is confident that pasteurization is effective at inactivating H5N1, and that the commercial, pasteurized milk supply is safe,” the agency stated. They also noted that while labeling regarding raw or pasteurized milk use is not federally mandated, many producers voluntarily disclose this information.
The FDA has stated that they are not aware of any H5N1 illnesses to date from the consumption of aged raw milk cheese products.
It remains unclear whether humans can be infected by consuming contaminated food. Further research is needed to fully understand the risks.
Disclaimer: The findings discussed in this article are based on a preprint study and should be considered preliminary until peer review and publication in a scientific journal. While health officials maintain that foodborne transmission is unlikely, ongoing research is crucial to fully assess the risks associated with consuming raw milk products. Consumers should consult with healthcare professionals for personalized advice.
