EPIDEMIOLOGIC-STUDY OF A FOOD-BORNE OUTBREAK OF ENTEROTOXIGENIC ESCHERICHIA-COLI O25-NM BY PULSED-FIELD GEL-ELECTROPHORESIS AND RANDOMLY AMPLIFIED POLYMORPHIC DNA ANALYSIS

This study investigated the applicability of molecular epidemiological techniques to the identification of the causal agent of an outbreak o f diarrhea caused by ingestion of food contaminated with enterotoxigen ic Escherichia coli (ETEC). The outbreak occurred at four elementary s chools in July 1996 and affected more than 800 people. Illness was mos t strongly associated with eating tuna paste (relative risk, 1.79; 95% confidence interval = 1.16 to 2.79; P = 0.0001). To evaluate the epid emiological characteristics of the pathogen, the DNAs from numerous is olated ETEC strains were subjected to randomly amplified polymorphic D NA analysis, pulsed-field gel electrophoresis of nuclease S1-treated p lasmid DNA, and analysis of genomic DNA restriction fragment length po lymorphisms. All ETEC isolates were of the O25:NM (nonmotile) serotype , which carries a heat-stable enterotoxin Ib gene. Genotypic analysis demonstrated that the strains isolated from the patients at all four s chools were identical. The isolates of ETEC O25:NM obtained from the t una paste that had been served for lunch at these schools were genetic ally indistinguishable from those isolated from the patients. Results suggest that this outbreak was food borne. The molecular biology-based epidemiological techniques used in this study were useful in characte rizing the causal agent in this food-borne epidemic.