Critical Points of Food Contamination with Human Noroviruses

Human noroviruses are identified as the leading cause of foodborne diseases in many countries worldwide. Since 2011, in the EU the number of outbreaks caused by viruses has more than doubled, while in the US they cause 5.5 million foodborne illnesses (58%) annually. Contributing factors are some of the characteristics of human norovirus like ability to replicate to high titers, low infectious dose, persistence and stability in the environment. Noroviruses are typically spread by the fecal–oral route and transmitted by contaminated food, water or aerosols, person-to-person contact, cross-contamination from surfaces and contact with fomites. Some critical issues for contamination of foods at risk are: (i) Contamination of water sources with enteric viruses, particularly those used for agricultural practices (crop irrigation, food processing). Food at risk are fresh produce like salads and berries and bivalve shellfish due to filter-feeding what enables the concentration of norovirus from polluted water in the digestive glands. (ii) Norovirus is highly infectious and could be shed in feces at very high numbers (up to 1011 particles/g) for prolonged times (more than 3 weeks), which indicates ease of spread by food handlers. Infected foods handlers are the source of 53% of norovirus foodborne outbreaks. Foods at risk are those that need extensive handling and ready-to-eat foods that do not undergo further processing. (iii) Human noroviruses are able to attach to inert surfaces and persist for up to 28 days on common foodpreparation surfaces. Likewise is their high survival on finger pads and transfer to, for example, stainless steel surfaces and successively to foods.