[Water-borne disease outbreaks in Norway]. / Sykdomsutbrudd forårsaket av drikkevann i Norge.

BACKGROUND: The drinking water in Norway has traditionally been considered being of good quality. However, outbreaks related to drinking water are reported every year. We review waterborne outbreaks in Norway over the last 15 years, and describe the aetiology of and contributory factors in these outbreaks. MATERIALS AND METHODS: We compiled data on waterborne outbreaks reported to the Norwegian Institute of Public Health and Norwegian Food Control Authority during 1988-2002. We included all events in which two or more people fell ill and water was the suspected source of infection. RESULTS: Over the 15-year period. 72 outbreaks were reported, affecting a total of 10 616 persons. Campylobacter was the cause in 26% (19/72) of the outbreaks, norovirus in 18% (13/72). The causative organism was unknown in 46% (33/72). The water came from public waterworks in 32 of the 54 outbreaks for which this information was available (59%); from a private supply in the remaining 22. For 62% (16/26) of the outbreaks related to waterworks, the water was not disinfected before distribution. None of the private water supplies were disinfected. Over the last five years, there were more outbreaks related to private supplies. INTERPRETATION: The most important contributory factor to waterborne outbreaks in Norway is contamination of the raw water combined with missing or faulty disinfecting procedures. To prevent future outbreaks, a continuous upgrading of small and private water supplies is needed. Reporting of outbreaks is important for the implementation of targeted and effective preventive measures.