Survival of influenza virus H1N1 and murine norovirus in raw milk cheeses.

The spillover of highly pathogenic avian influenza (HPAI) to dairy cattle and its presence at high titers in raw milk has created a concern that consumption of dairy products made from unpasteurized milk could result in human exposure. We examined whether H1N1, as a surrogate for HPAI viruses, and murine norovirus (MNV), as a surrogate for unenveloped enteric viruses, can survive the cheese-making process by making cream cheese-style and feta-style cheeses from artificially inoculated raw milk. We used the modified ISO 15216 method for viral extraction, which has a limit of detection of 3.0-3.7 log for infectious H1N1 in soft cheeses. Infectious H1N1 virus was detected in the curd from both types of cheeses and in the whey from cream cheese but not in the whey from feta cheese. Infectious MNV particles were detected in the curd and in the whey for both types of cheeses. To study the effect of salt, pH, aging, and microbiome of various unpasteurized milk cheeses on viral survival, we artificially inoculated different commercial unpasteurized milk cheeses with 7 log PFU of H1N1 and 6 log PFU of MNV and examined viral survival over an 8 week period at 4°C. We observed that H1N1 survived for 8 weeks, with an average of 2.6, 2.75, and 4.0 log reductions on cheddar, washed rind firm cheese, and semisoft brie-like cheese, respectively (