How do viruses enter the fruit and vegetables food chain and estimation of consumer risk

In developed countries a substantial number of foodborne disease outbreaks is caused by enteric pathogenic viruses. Contamination by viruses like noroviruses (NoV), hepatitis A virus (HAV) and hepatitis E virus (HEV) in foods does not correlate with indicator bacterial loads that are used for assessment of microbiological quality of food products. Typically also backtracking of foods such as shellfish and frozen berries is challenging; one batch includes berries picked at numerous farms and oysters from different cultivation areas can be mixed, even across borders. The viral contamination of food is closely linked to human population and sewage, except for the zoonotic HEV that is linked to animal products.

The viruses enter the soft fruit chain in production mainly via contaminated irrigation water and/or harvesters’ hands. During processing the critical points are washing and chlorination for leafy greens, freezing and packaging for soft fruit. Manual handling of food produce at point-of-sale has also to be taken into account. Recent epidemiological investigations of outbreaks have shown evidence about the role of asymptomatic food handlers in contaminating food. However, virus transmission by food handlers leading to outbreaks occurs often at food serving facilities rather than at food industry.

With data obtained by harmonized quantitative viral detection methods it is possible to build more accurate risk models and compare scenarios, although due to numerous data gaps many assumptions are still made. Here we describe our long-term experiences of analyzing NoV from foods, mainly soft fruits.