title: Precipitation and primary health care visits for gastrointestinal illness in Gothenburg, Sweden.
abstract: BACKGROUND
  The river Göta Älv is a source of freshwater for the City of Gothenburg, Sweden, and we recently identified a clear influence of upstream precipitation on concentrations of indicator bacteria in the river water, as well as an association with the daily number of phone calls to the nurse advice line related to acute gastrointestinal illnesses (AGI calls). This study aimed to examine visits to primary health-care centers owing to similar symptoms (AGI visits) in the same area, to explore associations with precipitation, and to compare variability in AGI visits and AGI calls.
  
  
  METHODS
  We obtained data covering six years (2007-2012) of daily AGI visits and studied their association with prior precipitation (0-28 days) using a distributed lag nonlinear Poisson regression model, adjusting for seasonal patterns and covariates. In addition, we studied the effects of prolonged wet and dry weather on AGI visits. We analyzed lagged short-term relations between AGI visits and AGI calls, and we studied differences in their seasonal patterns using a binomial regression model.
  
  
  RESULTS
  The study period saw a total of 17,030 AGI visits, and the number of daily visits decreased on days when precipitation occurred. However, prolonged wet weather was associated with an elevated number of AGI visits. Differences in seasonality patterns were observed between AGI visits and AGI calls, as visits were relatively less frequent during winter and relatively more frequent in August, and only weak short-term relations were found.
  
  
  CONCLUSIONS
  AGI visits and AGI calls seems to partly reflect different types of AGI illnesses, and the patients' choice of medical contact (in-person visits versus phone calls) appears to depend on current weather conditions. An association between prolonged wet weather and increased AGI visits supports the hypothesis that the drinking water is related to an increased risk of AGI illnesses.
authors.affiliation: Department of Public Health and Clinical Medicine, Division of Occupational and Environmental Medicine, Umeå University, Umeå, Sweden.
authors.forename: Andreas
authors.initials: A
authors.lastname: Tornevi
authors.affiliation: Department of Public Health and Community Medicine, Division of Occupational and Environmental Medicine, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Barregård
authors.affiliation: Department of Public Health and Clinical Medicine, Division of Occupational and Environmental Medicine, Umeå University, Umeå, Sweden.
authors.forename: Bertil
authors.initials: B
authors.lastname: Forsberg
mesh_terms: D000208:Acute Disease; D060766:Drinking Water / Q000382:microbiology*; D005767:Gastrointestinal Diseases / Q000175:diagnosis* / Q000382:microbiology; D015277:Hotlines / Q000706:statistics & numerical data*; D006801:Humans; D009819:Office Visits / Q000706:statistics & numerical data*; D011320:Primary Health Care / Q000706:statistics & numerical data*; D011891:Rain; D012044:Regression Analysis; D045483:Rivers / Q000382:microbiology; D012621:Seasons; D013548:Sweden; D014871:Water Microbiology; D014881:Water Supply
chemical_list: D060766:Drinking Water