The impact of a contaminated city water supply on an emergency department.

In March 2007 Galway City and County's water supply was officially contaminated by cryptosporidiosis. The medical and nursing staff at the city's only Emergency Department had noted a rise in an atypical form of gastroenteritis in the preceding months. A retrospective audit of 11,723 charts from January 1st 2007 to 22nd March (day after contamination was confirmed) was performed to identify these patients. The number of potential gastroenteritis cases was 185 (incidence 1.6%), with a peak five weeks before the outbreak was confirmed. Half the patients were aged between 20 and 34. Pain (80%), nausea or vomiting (74%) and diarrhoea (66.5%) were the most frequent symptoms. The mean duration of symptoms at presentation was 2 days. Stool samples were sent for nine patients and four of these were tested for Cryptosporidium. Over a quarter (28.6%) of patients were admitted and almost three-quarters (69.7% +/- 7%) had a residential address in the affected area. Difficulty exists in the early identification of new outbreaks and many of the affected patients are not detected using routine surveillance or current capture methods.