Association between Precipitation Upstream of a Drinking Water Utility and Nurse Advice Calls Relating to Acute Gastrointestinal Illnesses

BACKGROUND The River Göta Älv is a source of fresh-water for the City of Gothenburg (Sweden). We recently identified a clear association between upstream precipitation and indicator bacteria concentrations in the river water outside the intake to the drinking water utility. This study aimed to determine if variation in the incidence of acute gastrointestinal illnesses is associated with upstream precipitation. METHODS We acquired data, covering 1494 days, on the daily number of telephone calls to the nurse advice line from citizens in Gothenburg living in areas with Göta Älv as a fresh-water supply. We separated calls relating to gastrointestinal illnesses from other medical concerns, and analyzed their association with precipitation using a distributed lag non-linear Poisson regression model, adjusting for seasonal patterns and covariates. We used a 0-21-day lag period for precipitation to account for drinking water delivery times and incubation periods of waterborne pathogens. RESULTS The study period contained 25,659 nurse advice calls relating to gastrointestinal illnesses. Heavy rainfall was associated with increased calls the same day and around 5-6 days later. Consecutive days of wet weather were also found to be associated with an increase in the daily number of gastrointestinal concerns. No associations were identified between precipitation and nurse advice calls relating to other medical concerns. CONCLUSION An increase in nurse advice calls relating to gastrointestinal illnesses around 5-6 days after heavy rainfall is consistent with a hypothesis that the cause could be related to drinking water due to insufficient barriers in the drinking water production, suggesting the need for improved drinking water treatment.