MOLECULAR EPIDEMIOLOGY OF A FAST-FOOD RESTAURANT-ASSOCIATED OUTBREAK OF ESCHERICHIA-COLI O157 H7 IN WASHINGTON-STATE/

We studied the molecular epidemiology of the recent fast-food restaura nt chain-associated Escherichia coli O157:H7 outbreak in Washington St ate, Genomic DNAs prepared from strains isolated from 433 patients wer e probed with radiolabelled Shiga-like toxin (SLT) I and SLT II genes and bacteriophage lambda DNA and were subsequently analyzed for their restriction fragment length polymorphism (RFLP) patterns. The SLT RFLP and lambda RFLP profiles of an E. coli O157:H7 strain isolated from t he incriminated beef and prototype patient were compared with those of the patient isolates for determination of the concordance between pat terns. Of the 377 patients with primary and secondary cases of infecti on epidemiologically linked to the outbreak, isolates from 367 (97.3%) of the patients displayed SLT RFLP and lambda RFLP profiles identical to those of the outbreak strains, Isolates from 10 of the 377 (2.6%) patients possessed SLT RFLP and lambda RFLP profiles different from th ose of the outbreak strains, and the patients from whom those isolates were obtained were subsequently characterized as having non-outbreak- related infections. The E, coli O157:H7 strains isolated from 31 of 44 (70.4%) patients who were epidemiologically excluded from the outbrea k were linked to the outbreak by RFLP typing. Our results indicate tha t SLT RFLP and lambda RFLP analyses are stable and sensitive methods; and when they are used in conjunction with an epidemiological investig ation they could result in an earlier recognition of outbreaks and the ir sources, hence prompting measures to prevent the continued transmis sion of E, coli O157:H7.