AN OUTBREAK OF NORWALK-LIKE GASTROENTERITIS ASSOCIATED WITH CONTAMINATED DRINKING-WATER AT A CARAVAN PARK

During the 1989 Christmas holiday period, a large outbreak of gastroen teritis occurred among persons staying at a caravan park in southern N ew South Wales. Review of local hospital records found that 77 per cen t of patients presenting with infective diarrhoea between 29 December and 3 January had stayed at the caravan park. In a retrospective cohor t study we compared rates of illness among caravan park patrons expose d to different water sources. Stools were tested for pathogens and con valescent sera for viral antibodies. Rain and reticulated river water sampled from the caravan park were tested for bacteria and viruses. Of 351 persons interviewed at the caravan park, 305 (87 per cent) report ed an illness characterised by diarrhoea, vomiting and abdominal pain. Of 196 persons who used reticulated river water for drinking or ablut ions, 175 (89 per cent) became ill compared with 47 of 72 persons (65 per cent) who did not use this water (relative risk 1.4, 95 per cent c onfidence interval 1.2 to 1.6). The outbreak was probably caused by a 27-28 nm small round structured virus found in the stool from one ill person. High levels of faecal coliforms in the reticulated river water and enterovirus in sediment samples suggest that the outbreak was cau sed by sewage contaminating the reticulated river water through a brea k in the pipe directly over the underground water tanks. To prevent su ch outbreaks, poor water and sewerage system layouts should be avoided and nonpotable water should be clearly labelled. Where feasible, all camping-ground water should stem from town supplies.