The Health Protection Agency (HPA) and Environmental Health Officers from the Royal Borough of Windsor and Maidenhead Berkshire East Primary Care Trust have reported an in-depth investigation into what caused the outbreak at the Michelin-starred establishment. Investigations focused on laboratory testing of diners with symptoms of diarrhoea and vomiting (where possible); analysis of detailed questionnaires sent to others who reported similar illness; investigation of illness among staff; examination of the restaurant environment and food processing, handling and supply; laboratory testing of food samples. The main conclusions were that more diners who ate shellfish reported illness. The oysters were served raw and tracing of shellfish showed evidence of contamination and there have been reports of illness in other ventures associated with oysters from the same source. The restaurant co-operated fully with the investigation and was able to re-open in March. Restaurants that suspect food-poisoning among staff or diners should quickly seek advice and support from their local authority's environmental health team and the HPA. This can prevent incidents becoming prolonged outbreaks and reduce the number of diners and staff affected. HPA South East regional director, Dr Graham Bickler, said: "This investigation has been long, complex and thorough. It confirms the well-known risks that raw shellfish pose. Oysters and other shellfish can become contaminated with norovirus originating from human sewage, especially during winter months. "Individuals infected with norovirus can readily transfer the virus onto foods they prepare. The virus will remain viable and capable of causing illness in those foods that are not subsequently cooked…the more intensively that food is handled the more likely it is to become contaminated by infected food handlers."