Purpose: To conduct a quantitative risk assessment of human salmonellosis arising from the consumption of pistachios in the U.S. and to evaluate the impact of exceptional situations occurring prior to microbial reduction treatment.
Methods: A baseline exposure assessment model was developed that includes Salmonella prevalence and levels on floater and sinker pistachios in silo storage, microbial reduction treatment (0-5 log CFU), Salmonella persistence during post-processing and retail storage, and consumption levels. Exceptional situations occurring prior to microbial reduction treatment, including increasing the prevalence and levels of Salmonella cross-contamination in a float tank, Salmonella growth due to a delay in drying hulled pistachios, and Salmonella recontamination by pests in the storage silos, were each modeled with a subsequent microbial reduction treatment (0-5 log CFU). A homogeneous distribution of the Salmonella cells was assumed. Risks per serving and per exceptional situation were calculated using Monte Carlo simulations developed in R using the mc2d package. Variability was set to 10,001 replicates and uncertainty dimension to 501 replicates; these were modeled independently.
Results: The baseline model predicted a 90% reduction in risk of salmonellosis for each log of microbial reduction treatment level applied. The predicted relative risk of illness per pistachio serving was higher in the modeled exceptional situations – Salmonella cross-contamination in a float tank (6.8 to 7.5-fold higher), Salmonella recontamination by pests in the silos (1.0 to 1.2-fold higher), and Salmonella growth due to a delay in drying (1.1 x 102 to 4.3 x 108-fold higher) – when compared to the baseline model.
Significance: While process control through microbial reduction treatment is predicted to significantly reduce the risk from pistachio consumption, certain pre-processing exceptional situations may contribute to increased risk.