An outbreak of norovirus infection linked to oyster consumption at a UK restaurant, February 2010

Background We present the investigation of an outbreak of gastroenteritis at a UK restaurant incorporating both epidemiological and microbiological analysis. Methods Structured postal questionnaires were sent to 30 diners who ate at the restaurant during the outbreak period (5-7 February 2010). Stool specimens collected from staff and diners were submitted for bacterial culture and norovirus testing, and 15 Pacific oysters (Crassostrea gigas) from the batch served during the outbreak period were tested for norovirus. Results A strong association was observed between illness and oyster consumption (odds ratio undefined, confidence interval: 11.7 to infinity, P = 0.00001). Multiple different sequences of norovirus RNA were present in both stool and oyster specimens, typical of a shellfish origin. Several contemporaneous norovirus outbreaks throughout the UK were linked to oysters, particularly, though not exclusively, those sourced from Carlingford Lough in Ireland (as in this study), which were subsequently withdrawn from distribution. Conclusion Despite the risk to human health, there is significant uncertainty surrounding the quantitative correlation between oyster norovirus levels and consumer illness. Continued research should help further our understanding of this crucial correlation and identify ways in which viral depuration of oysters can be enhanced.