Outbreak of food-borne associated with oysters consumption caused by Norwalk-like virus

BACKGROUND: The aim of this study was to conduct a clinical-epidemiological and microbiological investigation into an outbreak of food-borne disease d ue to the consumption of oysters. PATIENTS AND METHODS: A historic cohort study was conducted into the consum ption of 15 food items and clinical symptoms. The influence of each foodstu ff was assessed by Mantel-Haenzel stratified relative risk (RRM-H) at 95% c onfidence intervals, and was confirmed by dose-response analysis with a chi (2) test tendency. We investigated sample stools from 5 patients and 2 food -handlers. Results: The overall attack rate was 38.0% (19/50). The median period of in cubation was 39.0 h (maxim 62 and minimum 3 h). The symptoms were: fever 17 .6% (3/17), diarrhoea 57.9% (11/19), vomits 84.2% (16/19), nausea 89.5% (17 /19) and abdominal pain 89.5% (17/19). In stratified analysis, the Mantel-H aenzel method revealed a statistically risk for oysters (RRM-H = 3.3; IC 95 %: 1.1-8.7), while the RRM-H value for sea snails was not significant (RRM- H = 2.8; IC 95%: 0.9-41.1). For oyster consumption, the dose-response test was statistically significant (p = 0.005). Examination by electron microsco py revealed small round structured Viruses compatible with Norwalk-like vir us. The oyster contamination was reported to the public health authority. CONCLUSIONS: This research highlights the usefulness of dose-response analy sis in presenting epidemiological evidence, reveals the potential role of o yster consumption in food-borne disease such us Norwalk-like virus and shaw the need for monitoring production centres and oyster beds in order to pre vent further cases of contamination.