Recent research conducted by Cornell University has revealed concerning findings about the persistence of H5N1 virus in raw milk cheese. The virus can survive for up to 60 days in cheese, depending on specific pH conditions, which challenges existing food safety assumptions about aging processes. This persistence occurs primarily at pH levels of 6.6 and 5.8, while the virus doesn’t survive at more acidic pH 5.0 environments. These results raise significant food safety concerns for aged raw milk cheese and other unpasteurized dairy products in light of ongoing avian influenza outbreaks.
Understanding the Cornell University Research
The groundbreaking study, funded jointly by the FDA and New York State, investigated how H5N1 virus behaves during the cheese-making process. Cornell University researchers created an experimental model where raw milk was intentionally spiked with H5N1 to produce cheese under varying acidity conditions. The team also examined raw milk cheddar cheese that had been inadvertently made with H5N1-contaminated milk to provide a real-world scenario assessment.
What makes this research particularly concerning is the discovery that infectious virus particles remain viable throughout the cheese-making process under certain pH conditions. The findings, published as a preprint on bioRxiv (though not yet peer-reviewed), challenge the long-held belief that the 60-day aging process for raw milk cheese eliminates harmful pathogens. This aging period has been the standard safety protocol for raw milk cheese in the United States for decades.
The pH level of cheese emerges as a critical factor in virus survival. At pH levels of 6.6 and 5.8, which are common in many cheese varieties, the virus remained detectable and infectious for the full 60-day study period. Only at the more acidic pH level of 5.0 did the virus fail to survive throughout the aging process.
FDA’s Response and Current Surveillance Efforts
In response to these findings, the FDA launched a comprehensive testing program for raw milk cheese in December 2024. The agency plans to test approximately 300 samples of 60-day aged raw milk cheese to evaluate whether current aging requirements provide adequate protection against H5N1 contamination. This proactive surveillance represents an important step in protecting public health.
The preliminary results from this testing program show no cause for immediate alarm. Of the 110 samples collected so far, 96 have tested negative for H5N1 using PCR testing, with 14 samples still in progress. No positive H5N1 samples have been detected in commercial products at this time, which is reassuring for consumers and dairy producers alike.
However, the FDA continues to monitor the situation closely as more test results come in. The agency has emphasized that this surveillance effort is aimed at evaluating the safety of the 60-day aging process, which has been the regulatory standard for raw milk cheese in the United States. The results will help determine whether additional safety measures might be needed for raw milk dairy products.
Public Health Implications of the Findings
The Cornell University research team noted a particularly concerning aspect of their findings: “Although the infectious dose of the virus to humans is not known, ingestion of contaminated raw dairy products repeatedly may increase the probability of infections.” This statement highlights the potential risk, especially for regular consumers of raw milk products. The accumulation of exposure through multiple consumptions could potentially increase infection risk even if individual exposures remain below infectious thresholds.
Despite these concerns, the Centers for Disease Control and Prevention (CDC) maintains that the current public health risk from H5N1 in dairy products remains low. This assessment is based on various factors, including the limited number of documented human infections despite widespread dairy industry challenges with H5N1. The CDC continues to monitor the situation and will update guidance as needed based on emerging evidence.
For consumers who enjoy artisanal cheeses, these findings might prompt reconsideration of raw milk cheese consumption, especially for vulnerable populations such as pregnant women, young children, elderly individuals, and those with compromised immune systems. Pasteurized milk cheeses provide a safer alternative while still offering excellent flavor and variety.
The Science Behind Virus Survival in Cheese
Understanding why H5N1 can survive in cheese requires examining the cheese-making process itself. During production, milk undergoes several transformations including curdling, draining, and aging. These processes create environments with varying moisture levels, salt concentrations, and pH values that affect microbial growth.
The cheese matrix – the physical structure of proteins, fats, and other components – can potentially shield viruses from environmental factors that would normally inactivate them. This protective environment may explain why H5N1 remains viable in cheese even after extended aging periods. The fat content in cheese might also play a role in protecting viral particles, as lipids can stabilize viral structures.
Interestingly, different cheese varieties create different microenvironments. Hard cheeses tend to have lower moisture content and higher salt levels, which generally inhibit microbial growth. However, as the Cornell study demonstrated, pH appears to be the determining factor for H5N1 survival rather than cheese type alone. This helps explain why the virus persisted at pH 6.6 and 5.8 but was inactivated at pH 5.0.
Previous assumptions about pathogen reduction during cheese aging were largely based on studies with bacterial contaminants rather than viruses. Viruses like H5N1 follow different survival patterns than bacteria, which may explain why the 60-day aging requirement – primarily designed for bacterial control – appears inadequate for certain viral pathogens.
Broader Context of Avian Influenza Outbreaks
The concern about H5N1 in dairy products exists within the larger context of avian influenza’s spread beyond bird populations. Recently, New York City health officials began investigating two cats infected with H5 avian flu, highlighting the virus’s ability to cross species barriers. These cases add to growing evidence that H5N1 is expanding its host range.
The USDA has also reported new H5N1 detections in poultry in Oklahoma and Philadelphia. These outbreaks demonstrate the ongoing challenge of containing the virus within the United States. The spread into dairy cattle in early 2023 represented a significant development, as it was the first documented instance of sustained transmission among cattle herds.
Globally, H5N1 continues to cause concern as it evolves and adapts to new hosts. While human infections remain rare, health officials maintain vigilance due to the virus’s potential to cause severe disease in humans. The FDA provides regular updates on avian influenza through its dedicated portal, which tracks developments and provides guidance for consumers and producers.
Alternative Dairy Options and Future Directions
For those concerned about potential risks associated with raw milk cheese, numerous alternatives exist in today’s diverse food landscape. Pasteurized milk cheeses undergo heat treatment that effectively inactivates viruses like H5N1 while still producing excellent flavor profiles. Many artisanal cheesemakers now create award-winning cheeses using pasteurized milk.
The growing plant-based dairy alternatives also offer options for consumers looking to avoid animal milk entirely. These products continue to improve in taste and texture, providing viable alternatives for those with health concerns or dietary preferences. Innovations in fermentation technology are also creating new possibilities for cultured dairy products with enhanced safety profiles.
Looking ahead, this research may prompt regulatory agencies to reevaluate safety standards for raw milk products. The current 60-day aging requirement was established based on different pathogen concerns, and the H5N1 findings suggest this standard may need updating. Future research will likely focus on identifying processing conditions that can reliably inactivate viral pathogens while preserving the qualities that make artisanal cheeses desirable to consumers.
In the meantime, I encourage cheese enthusiasts to stay informed about developments in this area while making personal choices that balance culinary preferences with health considerations. The FDA’s ongoing surveillance will provide valuable data to guide both regulatory decisions and consumer choices in the coming months.