Purpose: The objective was to develop a probabilistic model accounting for NoV transmission during vegetable preparation at school cafeterias.
Methods: A probabilistic risk model was constructed using Visual Basic program for Excel (Microsoft®, Redmond) and @Risk, add-in for Excel (Palisade©, New York). Different contamination scenarios were constructed based on structured food handling observations from 14 secondary school cafeterias in Kansas. Transfer rates, survival rates, disinfection treatment and hand washing efficacy were considered among other variables by defining probability with data collected from literature. The safety criterion was established to 10 PFU/serving. The output of the model corresponded to plaque-forming units (PFU) NoV per serving. In addition, a sensitivity analysis was conducted to assess the effect of the different variables on the final risk.
Results: Results for the pathway describing transfer from contaminated surface or handler to foods (P1) indicated that levels of ≤4 log PFU/fomite did not result in any servings with values >10 PFU/serving . When initial levels were higher, around 20% servings contained levels >10 PFU/serving (for a 7 log PFU/fomite scenario). In the pathway modeling transfer from contaminated vegetables to uncontaminated vegetables, prevalence was lower than the previous pathway, obtaining 10% of servings with >10 PFU/serving (when 7 log PFU/vegetable was the initial contamination level). However, concentration in this pathway was higher than in P1. Also, results indicated that contamination by contaminated work surfaces was more significant than by hands.
Significance: Based on sensitivity analysis, effective training programs specifically addressing food and non-food contact work area sanitation to minimize NoV transfers to fresh produce may be implemented to ensure food safety at school cafeterias.