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<p>This study applied a standardised, quantitative norovirus detection method to provide monthly surveillance data on up to 50 representative oyster harvesting locations across the UK over a 2 year period. A range of sites was selected based on relative risk of norovirus contamination according to pre-defined criteria. All samples will also be tested for E. coli as a generalised indicator of faecal contamination. In addition, pairs of sewage samples (crude and treated) from a sewage treatment works that potentially impacts on the selected oyster sites were collected fortnightly and tested for norovirus using an adapted CEN/ISO detection method.</p>
<p>Background: Contamination of bivalve shellfish with norovirus (causing gastroenteritis) is recognised as a major human health risk associated with the consumption of contaminated shellfish. Risk assessment and management relies on E. coli levels as an indicator of faecal (sewage) contamination in shellfish. However this is considered to be inadequate in determining the risk from human enteric viruses such as norovirus. There is currently a lack of quantitative data on the prevalence, distribution and levels of norovirus in oysters and oyster production/harvesting areas within the UK.</p>
<p>Over recent years considerable progress has been made towards the development of sensitive molecular methods (PCR) to detect norovirus in shellfish. The Centre for Environment, Fisheries and Aquaculture Science (Cefas) has developed a quantitative method for detection of norovirus in bivalve shellfish which targets the shellfish digestive glands (hepatopancreas), based on the CEN draft standard for detection of viruses in food.</p>
<p>The systematic surveillance data generated will be used to develop the Agency’s policy on virus contamination of bivalve shellfish and contribute to an EFSA review of data on norovirus in oysters expected to inform further discussions in Europe. </p>