Quantitative microbial risk assessment of human H5N1 infection from consumption of fluid cow's milk

The spillover of H5N1 clade 2.3.4.4b into dairy cattle has raised concerns over the safety of fluid milk. While no foodborne infection has been reported in humans, this strain has infected at least 70 people and milk from infected cows is known to be infectious by ingestion in multiple other species. Investigation into the public health threat of this outbreak is warranted. This farm-to-table quantitative microbial risk assessment (QMRA) uses stochastic models to assess the risk of human infection from consumption of raw and pasteurized fluid cow's milk from the United States supply chains. These models were parameterized with literature emerging from this outbreak, then employed to estimate the H5N1 infection risk and evaluate multiple potential interventions aimed at reducing this risk. The median (5^th, 95^th percentiles) probabilities of infection per 240-mL serving of pasteurized, farmstore-purchased raw, or retail-purchased raw milk were 7.66E-19 (2.39E-20, 4.02E-17), 1.56E-7 (6.67E-10, 1.28E-5), and 1.40E-7 (6.65E-10, 1.13E-05), respectively. Our results confirm that pasteurization is highly effective at reducing H5N1 infection risk. Scenario analysis revealed quantitative real-time reverse transcriptase-polymerase chain reaction (qrRT-PCR) testing of bulk tank milk to be an effective method for numerically reducing risk from raw milk. Additionally, we identify knowledge gaps related to human H5N1 dose-response by ingestion and raw milk consumption patterns. These findings emphasize the importance of mechanistic epidemiologic models for informing public health responses amidst outbreaks with foodborne potential and highlight the need for additional research into raw milk consumption patterns to better understand this exposure pathway.