A food-borne outbreak of hepatitis A virus (HAV) infection in a secondary school in Upper Normandy, France, in November 2006

In November 2006, six symptomatic cases of hepatitis A in pupils of a secondary school in Upper Normandy, France, were reported to the district health service. This paper describes the outbreak investigation undertaken with the aim to identify the vehicle and source of infection, implement control measures and estimate the size of the outbreak. A primary case at the secondary school was defined as a pupil or a member of the staff with IgM anti-HAV detected in the serum and with onset of symptoms between 12 and 21 November 2006; a secondary case was defined as a contact to a primary case and who developed symptoms and had IgM anti-HAV two to seven weeks later. We performed a case control study of primary cases, controls being pupils visiting the same school (cases/controls 1:4) and inspected the canteen facilities. All 13 canteen employees were examined for anti-HAV IgM antibodies. A phylogenetic analysis of HAV of cases was performed. We identified 10 primary and 5 secondary cases. Among primary cases 90% reported eating liver pate at the canteen compared to 62% among controls (OR 5.5, 95% CI 0.62-256.9).One liver pate sample contained markers of faecal contamination. HAV genotypes were of one identical type. All 13 canteen employees were negative for IgM anti-HAV while four had anti-HAV total antibodies. We found deficiencies regarding food preparing procedures and insufficient hand washing facilities. The vehicle of the outbreak was believed to be the liver pate but the source of HAV could not be identified. Insufficient facilities in the canteen hindered staff from maintaining a high hygiene standard and were subsequently improved.