Quantitative farm-to-fork human norovirus exposure assessment of individually quick frozen raspberries and raspberry puree.

A quantitative human norovirus (NoV) exposure model describing transmission of NoV during pre-harvest, harvest and further processing of soft red fruits exemplified by raspberries is presented. The outcomes of the model demonstrate the presence of NoV in raspberry puree or individual quick frozen (IQF) raspberry fruits and were generated by Monte Carlo simulations by combining GoldSim® and @Risk® software. Input data were collected from scientific literature, observational studies and assumptions. NoV contamination of soft red fruits is assumed to take place at farms by application of contaminated water for pesticides dilution or by berries' pickers shedding NoV. The model was built simulating that a collection center received berries from ten farms with a total of 245 food handlers picking soft red fruits during a 10-hour day shift. Given 0, 5 and 20 out of 245 berries' pickers were shedding NoV, these conditions were calculated to result in a mean NoV contamination of respectively 0.47, 14.1 and 36.2 NoV particles per kg raspberries in case all raspberries are mixed to one day-batch of 11tons. The NoV contamination of the fruits was mainly driven by the route of NoV shedding food pickers (95.8%) rather than by spraying contaminated pesticide water (4.2%) (baseline scenario with 5 shedding pickers and contaminated pesticide water). Inclusion of appropriate hand washing procedures or hand washing followed by hand disinfection resulted in estimated reductions of the mean NoV levels from 14.1 to 0.16 and 0.17 NoV particles per kg raspberries, respectively, for the baseline scenario with 5 out of 245 food pickers shedding NoV. The use of a mild heat treatment (30s at 75°C) during further processing of berries to purees was noted to reduce mean NoV levels substantially from 14.1 to 0.2 NoV particles per kg raspberry puree. For IQF raspberries, the NoV contamination is heterogeneously distributed and resulted in a mean contamination of 3.1 NoV particles per 250g package containing approximately 115 berries. This farm-to-fork model is a useful tool for evaluating NoV mitigation strategies in the soft red fruit supply chain.