Purpose: The objective of this study was to develop a QMRA of consumption of raw oysters contaminated with norovirus, to populate the assessment with data from well-characterized outbreaks, and evaluate the dose-response relationship for circulating strains of norovirus.
Methods: A 2D Monte Carlo-based exposure model was developed in Crystal Ball (Oracle Corp., Redwood Shores, CA) and used to simulate dose of norovirus per serving of raw oysters in well-characterized outbreaks. Dose was modeled based on published concentration and occurrence of virus in the oysters, serving size, and an estimate of percentage of particles that are infectious (10 to 100%). Previously characterized dose-response models were then used to estimate the probability of illness. Predicted illness rates were compared to actual reported illness rates for the reported outbreak conditions.
Results: The exposure module estimated dose levels in the range of 25,000 to 43,000 copies of norovirus per serving of oysters. At these doses, the estimated probability of infection ranged from 0.50 to 0.63 depending on the dose-response model. The results demonstrate that the dose-response models provide estimates consistent with observed attack rates (46 and 67%) in examined outbreaks.
Significance: The modeled dose range (25,000 to 43,000 copies) for the examined outbreaks is in a region where the previously proposed dose-response models converge. Additional outbreak analysis or clinical studies are needed in the lower range of doses where the dose-response models diverge to further evaluate the models for circulating strains of norovirus.