Modeling of norovirus transmission during slicing and quantitative risk assessment of human norovirus transmission in a foodservice system

Human norovirus is the leading cause of outbreaks of acute non-bacterial gastroenteritis worldwide. Recent epidemiological evidence indicated that preparation of fresh produce for use as ingredients in ready-to-eat food in commercial settings has been a significant source of the norovirus infections in the United States. In this dissertation, to help understand the cross-contamination of norovirus during preparation and service of fresh produce product in foodservice systems, we analyzed spread pattern of norovirus from a single tomato to many others via the use of a commercial slicer. Murine norovirus (MNV) was used as a surrogate. A non-linear regression equation was generated: y = -0.903* ln(x) + 7.945, (R² = 0.91), where y = log MNV per slicing and x = tomato number. The MNV levels transferred generally decreased as the number of tomatoes sliced increased, with some exceptions. Infrequent but erratic transfers, where the MNV level of a subsequent tomato was higher than that of a preceding tomato, occurred in later transfer of some trials. This study illustrates the complex nature of risk prediction associated with norovirus cross-contamination during food preparation in commercial establishments. We also developed a simulation model to quantify the overall effect of norovirus cross-contamination in a food service establishment. For each possible source of initial contamination, using a manual tap versus a hands-free faucet were studied at 0, 30, 50, 70, and 100% handwashing compliance levels to check the number of salads and employees that may end up carrying more than 10 norovirus. When a lettuce/tomato was the initial source of contamination, change of knife and cutting board/slicer every 100 lettuce/tomato units was simulated. Change of tongs after preparation of every 100 salads was also simulated when a manual tap was used. Our model provides valuable information that can be considered for the control of NoV outbreaks. The results from our study suggested that multiple factors should be considered to control the spread of NoV, and that no one or even multiple combinations of factors will completely control NoV transmission risk.Ph. D.Includes bibliographical referencesIncludes vitaby Di L