Evidence of the presence of viral contamination in shellfish after short rainfall events

Infectious diseases linked to the consumption of raw shellfish have long been identified. Over the past century, various strategies have been set up in shellfish growing areas throughout the world to guarantee the sanitary quality of shellfish and to protect consumers. However despite sanitary improvements, human enteric viruses especially Hepatitis A virus and norovirus– have been found to be associated with shellfish outbreaks. A recent example demonstrated the impact of storm events. Following heavy rain and sewage overflow, shellfish beds were contaminated and the shellfish from them were marketed after depuration. However, since viruses persist longer than fecal contamination indicator bacteria, several clusters of gastroenteritis cases were reported. Analysis of both clinical and shellfish samples showed the presence of up to eight different strains of viruses: norovirus genogroup I genogroup II, astrovirus, and rotavirus, all strains being identical between clinical and environmental samples. Finding such a mixture is an indication of a fecally contaminated source such as sewage, especially in winter when a high diversity of strains may be present. In the future, standardization of methods, a better understanding of virus epidemiology will lead to improved shellfish safety for the consumer and to protect shellfish growing areas and to identify all possible sources of contamination.