It is difficult to assess the potential health impact of these findings, as the available research techniques are not able to differentiate between infectious and non-infectious norovirus material within the oysters. Furthermore, a safe limit for norovirus has not been established.
Between 2009 and 2011, scientists from the Centre for Environment, Fisheries and Aquaculture Science (Cefas), on behalf of the Food Standards Agency, took samples from 39 oyster harvesting areas across the UK. More than 800 samples of 10 oysters each were tested.
The research will contribute to a European Food Safety Authority review of norovirus levels in oysters, which will advise the European Commission on setting a specific legal safe level for norovirus in oysters placed on sale in the EU. The Agency and the shellfish industry are also continuing to work together to develop controls for norovirus.
Andrew Wadge, Chief Scientist at the Food Standards Agency, 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.
‘Though oysters are traditionally eaten raw, people should be aware of the risks involved in eating them in this way,’ he explains. ‘The Agency advises that older people, pregnant women, very young children and people who are unwell should avoid eating raw or lightly cooked shellfish to reduce their risk of getting food poisoning.’
David Lees, the lead investigator at Cefas, said: ‘We were fortunate to have excellent cooperation from the oyster producers and from local authority officers in conducting this study. Norovirus is a recognised problem for the sector, and this study provides important baseline data to help the industry and regulators to focus on the key risks.’