Risk of Fetal Mortality After Exposure to Listeria monocytogenes Based on Dose‐Response Data from Pregnant Guinea Pigs and Primates

One‐third of the annual cases of listeriosis in the United States occur during pregnancy and can lead to miscarriage or stillbirth, premature delivery, or infection of the newborn. Previous risk assessments completed by the Food and Drug Administration/the Food Safety Inspection Service of the U.S. Department of Agriculture/the Centers for Disease Control and Prevention (FDA/USDA/CDC)(1) and Food and Agricultural Organization/the World Health Organization (FAO/WHO)(2) were based on dose‐response data from mice. Recent animal studies using nonhuman primates(3,4) and guinea pigs(5) have both estimated LD50s of approximately 107 Listeria monocytogenes colony forming units (cfu). The FAO/WHO(2) estimated a human LD50 of 1.9 × 106 cfu based on data from a pregnant woman consuming contaminated soft cheese. We reevaluated risk based on dose‐response curves from pregnant rhesus monkeys and guinea pigs. Using standard risk assessment methodology including hazard identification, exposure assessment, hazard characterization, and risk characterization, risk was calculated based on the new dose‐response information. To compare models, we looked at mortality rate per serving at predicted doses ranging from 10−4 to 1012 L. monocytogenes cfu. Based on a serving of 106 L. monocytogenes cfu, the primate model predicts a death rate of 5.9 × 10−1 compared to the FDA/USDA/CDC (fig. IV‐12)(1) predicted rate of 1.3 × 10−7. Based on the guinea pig and primate models, the mortality rate calculated by the FDA/USDA/CDC(1) is underestimated for this susceptible population.