Potential role of asymptomatic kitchen food handlers during a food-borne outbreak of norovirus infection, Dublin, Ireland, March 2009

In March 2009, the Department of Public Health in Dublin, Ireland, was notified of a cluster of four gastroenteritis cases among people who attended a family lunch in a Dublin hotel. A retrospective cohort study was carried out. An outbreak case was defined as an attendee who developed diarrhoea and/or vomiting in the 60 hours following the lunch. Of 57 respondents, 27 met the case definition. Consumption of egg mayonnaise, turkey with stuffing or chicken sandwiches were each associated with increased risk of gastroenteritis: (risk ratio (RR): 2.3; 95% CI: 1.4–3.9), (RR: 1.9; 95% CI: 1.2–3.2), (RR: 1.9; 95% CI: 1.1–3.1), respectively. An environmental investigation established that before notification of the cluster, there had been unreported gastroenteritis among staff at the hotel. The earliest symptomatic person identified was a staff member who had vomited in the staff toilets but had not reported it. The sandwiches had most likely been contaminated by three asymptomatic kitchen food handlers who had used the same toilets. Stool samples were submitted by eight cases and 10 staff members. All eight cases and three asymptomatic food handlers on duty at the lunch tested positive for norovirus genogroup II.4 2006. Our analysis suggests that asymptomatic food-handlers can be responsible for norovirus transmission.