Waterborne disease in Norway: emphasizing outbreaks in groundwater systems.

In this study, we compiled and examined available data on waterborne disease outbreaks (1984-2007) in Norway, with emphasis on groundwater systems. A total of 102 waterborne outbreaks and 17,243 disease cases were reported during the period 1984-2007. The proportion of outbreaks related to groundwater reflected the proportion of groundwater works in Norway (40%). The proportion of disease cases corresponded to the proportion of persons supplied by groundwater (15%). Norovirus was identified as the most important disease causing agent in groundwater systems. No clear seasonal correlation was observed for Norovirus outbreaks in groundwater, but the largest outbreaks occurred during winter season. All outbreaks of campylobacteriosis occurred during March to November, with a peak in July-September, which correlates with the occurrence of coliforms in Norwegian groundwater in bedrock wells.