Contaminated food is a significant vehicle for human norovirus transmission. The present study determined the effect of physicochemical treatments on the tenacity of infective human norovirus genogroup II in selected foods. Artificially contaminated produce was subjected to a number of processes used by the food industry for preservation and by the consumer for storage and preparation. Virus recovery was carried out by using ultrafiltration and was monitored by using bacteriophage MS2 as an internal process control. Norovirus was quantified by using monoplex one-step TaqMan real-time reverse transcription (RT)-PCR and an external standard curve based on recombinant RNA standards. An RNase pretreatment step was used to avoid false-positive PCR results caused by accessible RNA, which allowed detection of intact virus particles. Significant reductions in titers were obtained with heat treatments usually applied by consumers for food preparation (baking, cooking, roasting). Generally, processes used for preservation and storage, such as cooling, freezing, acidification (>pH 4.5), and moderate heat treatments (pasteurization), appear to be insufficient to inactivate norovirus within a food matrix or on the surface of food. Besides data for persistence in processed food, comparable data for individual matrix-specific protective effects, recovery rates, and inhibitory effects on the PCRs were obtained in this study. The established procedure might be used for other noncultivable enteric RNA viruses that are connected to food-borne diseases. The data obtained in this study may also help optimize the process for inactivation of norovirus in food by adjusting food processing technologies and may promote the development of risk assessment systems in order to improve consumer protection.Norovirus (NV) (formerly Norwalk-like virus) is a member of the family Caliciviridae and is a nonenveloped virus with a single-stranded RNA (ssRNA) genome. Genetically, the human noroviruses are subdivided into three distinct genogroups (genogroup I [GGI], GGII, and GGIV) and into at least 31 genetic clusters or genotypes (53). Noroviruses have emerged as the most common cause of food-borne outbreaks and sporadic cases of acute nonbacterial gastroenteritis worldwide (62,87).In addition to direct person-to-person infection, transmission via environmental contamination (70) and transmission via foods and drinking water (primary and secondary contamination) are known. Food can be contaminated by contact with sewage or sewage water before harvest; e.g., shellfish (3,52,58,60,81) and raspberries (33, 72) have been reported to be vehicles of NV infection. Food is often directly contaminated during production, storage, distribution, and preparation by infected persons (22); e.g., ill or asymptomatic food handlers have been identified as sources of virus contamination of fresh produce and ready-to-eat foods (25, 69). The percentage of cases that can be attributed to food-or waterborne transmission is estimated to be between 16% (56) and 57% (34). Hu...
