Cheeses made with raw milk have gained immense popularity in the United States and worldwide due to their rich flavors and textures. However, these products must be aged for a minimum of 60 days to effectively inactivate bacterial pathogens. Recent findings concerning the detection of H5N1 avian flu in dairy cattle have sparked significant concern regarding whether this aging process can similarly disable the virus. A study conducted by scientists from Cornell University, recently reported on bioRxiv, suggests that the answer is predominantly no.
The research, which was funded by the U.S. Food and Drug Administration (FDA) and the state of New York, aims to evaluate the potential threat of H5N1 avian flu contamination in raw milk cheese. In addition to this research, the FDA announced an initiative in December 2024 to test nearly 300 samples of 60-day aged raw milk cheese. As of today, the FDA has provided an update on its findings, reporting that of 110 samples collected thus far, 96 tested negative for H5N1 using polymerase chain reaction testing. Testing on 14 additional samples is still ongoing, with no positive results for H5N1 reported at this time.
The Cornell study, which has not undergone peer review yet, involved creating raw milk cheese from milk intentionally contaminated with H5N1. The researchers conducted experiments at various pH levels, ranging from 6.6 to 5.0—all classified as acidic. They also evaluated samples of raw milk cheddar cheese that were unintentionally produced using H5N1-contaminated milk after an outbreak occurred on a dairy farm.
Results showed that the infectious virus was present throughout the cheese-making process and remained viable for up to 60 days of aging at pH levels of 6.6 and 5.8. However, at the most acidic pH level of 5.0, the virus did not survive, supporting previous studies indicating that influenza A viruses are sensitive to acidic environments. The study's authors warned that the repeated consumption of contaminated raw dairy products could potentially increase the risk of infections.
These findings not only raise concerns about the safety of aged raw milk cheese but also highlight potential risks associated with other raw milk products. The researchers noted that H5N1 can persist for up to 56 days when refrigerated, which could pose a significant risk to public health. Although the infectious dose of the virus in humans is not established, the team emphasized that repeated ingestion of contaminated products may heighten the likelihood of infections.
In related news, the New York City Health Department reported that it is investigating cases of H5 avian flu in two cats from separate households. Officials did not disclose how the cats were exposed to the virus but urged pet owners to refrain from feeding their pets raw food or raw milk. They recommended keeping animals indoors to prevent contact with wild birds or other potential carriers of the virus. Health authorities also reassured the public that the risk to humans remains low.
