More than three-quarters of British-grown oysters contain norovirus, new research from the Food Standards Agency (FSA) has found.
The study, which tested 39 UK growing beds across the UK, discovered that 76% of oysters had traces of the winter vomiting bug, with low levels of the virus, which can cause vomiting and diarrhoea, found in more than half (52%) of the contaminated samples.
However, the FSA said it was "difficult" to assess the potential health impact of the findings, as the available research techniques are unable to differentiate between infectious and non-infectious norovirus material within the oysters.
Nonetheless the results of the study will be used as part of a review by the European Food Safety Authority, which is to advise the European Commission on setting legal safety standards for norovirus in oysters, which currently have not been established.
Commenting on the report, Andrew Wadge, chief scientist at the FSA, said: "This research is the first of its kind in the UK. It will be important to help improve the knowledge of the levels of norovirus found in shellfish at production sites.
"The results, along with data from other research, will help us work with producers to find ways to reduce the levels of norovirus in shellfish, and work within Europe to establish safe levels."
Between 600,000 and one million people in the UK catch norovirus every year, with most infections thought to be spread from person to person.
In 2009, Heston Blumenthal closed the Fat Duck for two weeks after more than 500 diners were struck down by norovirus after eating contaminated shellfish at the three-Michelin-starred restaurant.
Blumenthal later received £200,000 compensation for lost business over the period while environmental health officials investigated.
By Kerstin Kühn
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