In Oct. 2010, a massive outbreak of Salmonella enterica serotype 4, 5, 12: i- sickened about 600 students in schools in Poitiers, France. For that many students to get sick, there was a massive contamination, probably coupled with massive failures in storage and preparation. At the time, there was extensive criticism regarding the failure to communicate the severity of the outbreak (in a Cool hand Luke sorta way, see clip).

These issues are not discussed in a new report by the Institut de Veille Sanitaire, but the epidemiological investigation is presented.

In October 2010, a salmonella outbreak occurred in schools in Poitiers. Salmonella enterica serotype 4, 5, 12: i- was isolated from stool samples of the first cases. Environmental investigations identified frozen beef burger meat from a single brand served in schools as the cause of the outbreak and food trace-back investigation led to identification and recall of beef burger. We conducted an investigation to assess the extent of the outbreak in the schools of Poitiers.

We conducted a retrospective cohort study. A self-administered questionnaire was filled by students and personnel attending the four exposed schools with cases. Clinical cases were defined as anyone reporting diarrheal or fever with at least one digestive sign within 5 days after school meal. We computed relative risks (RR) with their 95% confidence intervals (95%CI) and used the proportion test.

We identified a total of 554 cases (544 adolescents and 10 adults) of the 1559 responders (response rate 86%) who ate at school on the day the burger meat was served. The overall attack rate was 36,5%. Attack rate was significantly lower for one school (17%, p <0,01) compared to the three others. Adolescents (<20 years) were at greater risk than adults to develop signs (RR= 2,3; 95%CI 1,3-4,2). A total of 286 cases (53%) sought medical care, of which 31(6%) were hospitalized >24 hours. Concentration of salmonella in burger meat varied between 270 and 18,000 CFU/g³.

The serotype 4,5,12:I was associated with a severe outbreak, the largest salmonella food borne outbreak ever documented in a school setting in France. Quick identification and recall of incriminated batch is crucial to limit extension of outbreak.

Thanks to Albert Amgar for passing along the report.