Waterborne outbreaks: a public health concern for rural municipalities with unchlorinated drinking water distribution systems

OBJECTIVES: The objective of this study is to describe an important waterborne outbreak of gastrointestinal illness observed in a rural municipality of Quebec. METHODS: A population-based retrospective cohort study was conducted to identify risk factors associated with acute gastroenteritis. Indirect surveillance data were used to estimate the extent and the resolution of the epidemic. RESULTS: The cohort consisted of 140 randomly selected individuals of whom 22 met the illness case definition (15.7% attack rate). The epidemic curve was similar to the evolution of antidiarrheal products sold by the only pharmacy in town and calls made to the Health Info Line. Bivariate analysis led to identifying five risk factors of gastrointestinal illness: consumption of municipal water, contact with someone with acute gastroenteritis (within and outside of the household), contact with a child in daycare, and being less than 35 years of age. Drinking municipal water had the highest risk ratio (RR = 24.31; 95% CI = 1.50-393.4). Drinking water from a private artesian well was a protective factor (RR = 0.28; 95% CI = 0.09-0.90). CONCLUSION: This study highlighted that managing the risks associated with the consumption of untreated drinking water remains an important public health challenge, particularly in small rural municipalities vulnerable to climate variability.