Epidemiological and serological investigation of a waterborneCampylobacter jejunioutbreak in a Danish town

Abstract

SUMMARY: Following an unusually heavy rainfall in June 2009, a community-wide outbreak ofCampylobactergastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis.Campylobacter jejunibelonging to two relatedflaAtypes were isolated from stool samples. Serum antibody levels againstCampylobacterwere significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. This geographically constrained outbreak presented an ideal opportunity to study the serological response in persons involved in aCampylobacteroutbreak. The serology indicated that asymptomatic persons from the same household may have been exposed, during the outbreak period, toCampylobacterat doses that did not elicit symptoms or alternatively had been exposed toCampylobacterat a time prior to the outbreak, resulting in residual immunity and thus absence of clinical signs.