Health Stream Literature Summary - Issue 50 - June 2008

Outbreak of acute gastroenteritis of unknown etiology caused by contaminated drinking water in a rural village in Austria, August 2006
Meusburger, S., Reichart, S., Kapfer, S., Schableger, K., Fretz, R. and Allerberger, F. (2007) Wiener Klinische Wochenschrift, 119(23-24); 717-21.

Austria is a country with abundance of water resources and where the quality of these natural water resources usually allows delivery of drinking water as untreated spring water or untreated groundwater. In August 2006 a family doctor in a rural village reported the occurrence of a cluster of acute gastroenteritis cases. A waterborne outbreak was suspected and water samples were taken from the four springs, the reservoir and two outlets at point of use for bacteriological investigation, and chlorine disinfection of the community’s water reservoir was implemented. An investigation was undertaken by the public health authority of the province in order to determine the magnitude of the outbreak, the source of infection and to prevent further transmission.

The investigators had to rely on voluntary cooperation from physicians and patients for descriptive epidemiology. Data was collected by a local police officer on age and sex distributions for cases as permission to analyse the medical records for age and sex distributions was not granted. There were 160 cases of acute gastroenteritis identified by interviewing two physicians, and three cases required hospitalisation. Disease duration was found to range from 2 to 5 days. Age and sex distribution for 146 cases were available; ages ranged from 5 to 91 years, 65 were male and 81 were female. Stool samples from 14 of 114 cases seen by one physician were sent for bacteriological analysis; all tested negative for Salmonella, Campylobacter, Shigella and Yersinia enterocolitica. None of the specimens were tested for viruses, parasites or pathogenic Escherichia coli.

The water system serving the affected village consists of four springs originating in a mountainous area of karst formations feeding into one reservoir. Karst areas are known for their porosity and low capacity to cope with heavy rain. All except two water samples initially collected when the outbreak was recognised were found to be contaminated with Escherichia coli (greater than 20 CFU/ml). The two negative samples were from the two outlets at point of use and showed increased total heterotrophic count but were free of faecal indicator organisms at that time. Samples taken a few days later from all four springs and two further outlets at point of use were all found to be contaminated with E. coli and enterococci. Samples collected after the peak of the outbreak complied with legal requirements. Routine samples collected from the springs and three outlets at point of use two months previously were all free of contamination with faecal indicator organisms.

This is the first published outbreak of acute gastroenteritis due to contaminated drinking water in Austria. It is thought that the cluster of cases was caused by faecal contaminated of untreated drinking water. Microbiological investigation of the water indicated that the most likely cause of contamination was the introduction of faecal bacteria during extremely heavy and extensive rain falls that started at the beginning of August. Possible sources included grazing cattle, wild deer or tourists hiking in the area. Despite recognition of the outbreak and evidence of drinking water contamination, few stool specimens were tested for pathogenic microoganisms and no pathogens were identified. the authors suggest that medical practitioners should be encouraged to order microbiological testing beyond the routine tests in outbreaks of gastroenteritis as the spectrum of routine laboratory tests on stool specimens does not cover the wide range of pathogens capable of causing waterborne outbreaks. As possible future contamination of springs in karst areas may occur, the water department of this district authority has requested installation of a permanent ultraviolet water treatment facility.