[Case control studies in investigation of food-borne infection outbreaks. Study of their utilization in France].

Among the 251 foodborne outbreaks investigated by public health officers in France in 1989, 62 (25%) used a case-control study to identify the responsible food. This survey aims to analyse the results of these 62 investigations. Thirty eight (61%) investigations found the responsible food(s); 10 investigations (16%) lacked power because of the small size of the population studied, but allowed to suspect the food with the highest odds ratio; 13 investigations (21%) gave results inconsistent with bacteriological studies or with hypothesis generated by the descriptive study: in 5 of it, food origin is questionable and in 8 investigations, methodological errors are likely. We could not conclude for one study. Among the surveys with case-control studies, 74% identified the food responsible with bacteriological or epidemiological confirmation, as opposed to 17% of other surveys which had only bacteriological confirmation. This study allowed us to give recommendations on the management of investigation and the interpretation of results to improve the efficiency of this practice.