Estimating the risk of gastrointestinal illness associated with drinking water in Norway: a prospective cohort study

Abstract Background: The delivery of safe drinking water has high public health relevance, as reflected in the Sustainable Development Goals (SDG6). Several precautionary actions have resulted in a minimum burden associated with infectious diseases in high-income countries; however, there is increased awareness that the distribution system represents a risk factor for gastrointestinal illness. Sporadic cases of waterborne infections are expected to be underreported since a sick person is less likely to seek healthcare for a self-limiting gastrointestinal infection. Hence, knowledge on the true burden of waterborne diseases is scarce. Methods: We conducted a cohort study of self-reported gastrointestinal infections and water consumption to estimate the risk of acute gastrointestinal infection (AGI) associated with drinking water in Norway. Results: In total, 9,946 persons participated in this cohort study, accounting for 11.5% of all invited participants. Overall, we found a relatively low number of AGI per 100 person-months (5.5) and a very low number of severe AGI per 100 person-months (0.8). There were no clinically significant associations between the consumption of tap water and AGI or severe AGI in the models adjusted for possible confounders, with the expectation of a small effect of age on AGI. The risk of AGI was higher among small children (0-5 years; 5 percent points higher risk of AGI than among those 19-49 years old). AGI varied by season, but other possible confounding variables (sex, education level and size of water supply) were not statistically or clinically significant. Conclusions: This is the largest cohort study in Norway estimating the burden of self-reported gastrointestinal infections linked to the consumption of drinking-based water in Norway. Overall, the results from the adjusted model show either no or very small associations of AGI or severe AGI with water consumption (glasses of water consumed). There was a small association with age. The data indicate that water-related AGI is not currently a major burden in Norway, but the findings need to be used with caution. The importance of continued efforts and investments in the maintenance of drinking water supplies in Norway to address the low burden of sporadic waterborne cases and to prevent future outbreaks needs to be emphasised.