Purpose: Develop and apply a quantitative microbial risk assessment (QMRA) model that simulates the likelihood and magnitude of NoV contamination of produce from infected workers during harvest and packing.
Methods: A stochastic QMRA model was developed in R using data (derived from the literature or experts) on key parameters related to: NoV load on worker hands, worker behavior, and transfer, persistence, and dissemination of NoV. A stochastic sensitivity analysis identified the most relevant parameters. Scenario testing assessed the impact of hand washing, reduced produce contact, and worker illness severity on produce contamination.
Results: Produce contamination was greatest for the first several items harvested immediately after infected workers used the restroom, declining by over 2 log to approximately 20 virions/cm2 by the 10th item. Complete compliance of workers with recommended handwashing reduced contamination by 26.3% (SD = 33.2%) (packers) and 20.2% (SD = 23.8%) (harvesters), compared to the baseline model. A doubling of handwashing efficacy reduced contamination by 29.9% (SD = 35.2%). Contamination of produce declined to a negligible level (10 virions/cm2) when both packers and harvesters were shedding less than 107 NoV virions/g stool. This suggests that it might be relatively safe for workers to return after the period of peak viral shedding has passed, as long as they adhere to rigorous hand hygiene.
Significance: QMRA modeling can identify key factors that contribute to NoV transmission and allows for prioritization by magnitude of these effects. Model results support guidelines that reduce acutely ill workers’ contact with produce and encourage brief furlough and handwashing compliance to reduce the risk of NoV contamination.