[Contamination of a water system with sewage]

The purpose of the study was to examine the extent of illness caused by contamination of a waterworks with waste water due to overflow. Structured questionnaires were mailed to all 703 households (the main study group) and four day-care centers supplied by the waterworks as well as a group of 200 randomly chosen households in neighbouring communities with a different water supply. Fourteen hundred and fifty-five persons (88% of respondents in the main study group) reported that they had had symptoms of gastroenteritis, particularly diarrhoea (83%) and vomiting (55%). In the control group, 10% of respondents had had symptoms of gastroenteritis. Onset of diarrhoea correlated well with precipitation (Spearman's correlation coefficient: 0.75; p = 0.0002). No pathogens were found. It is important to be aware of the possibility of water contamination when an increased number of cases of gastroenteritis are observed in a local area and to report even a suspicion of waterborne diseases to the county public health office.