Health Stream Literature Summary - Issue 58 - June 2010

Waterborne disease in Norway: emphasizing outbreaks in groundwater systems.
Kvitsand, H.M.L., Fiksdal, L. (2010) Water Science and Technology, 61(3); 563-571.

Groundwater is the primary drinking water source for 15% of the population in Norway. The majority (2/3) of these systems are community systems and the remainder are small individual water systems. Most of the individual and smaller community waterworks in Norway supply groundwater directly from a spring or well without treatment as groundwater is generally considered a safe drinking water resource. Source protection is therefore vital for such water supply systems so that public health is not compromised. Microorganisms which cause disease may be discharged into the environment from a variety of sources and move through the soil and enter groundwater and this represents a risk of disease outbreaks. Outbreaks associated with groundwater have been reported in Norway but there is limited knowledge of the frequency and causes of outbreaks. This study was undertaken to compile and examine available data on waterborne disease outbreaks in Norway during 1984-2007 with emphasis on groundwater system outbreaks.

Information was complied on waterborne disease outbreaks (WBDO) that were reported to the Norwegian Institute of Public Health (NIPH) during 1988 to 2007. Information on WBDOs during 1984 to 1987 was based on the publication by Stenstrom et al in 1994 which included international publications, reports from Norwegian Surveillance System for Communicable Diseases (MSIS) or reports from local investigations.

There were 102 waterborne outbreaks and 17,243 disease cases reported during 1984-2007 in Norway. Of the outbreaks, 81 were from drinking water systems with a known type of water source, of which 46 occurred in surface water systems and 35 in groundwater systems. There were four outbreaks which occurred when persons consumed water that was not intended for drinking directly from rivers or lakes during outdoor activities. The total annual number of outbreaks varied from 0 to 12, with an average of 4.3 outbreaks per year. The average number of persons affected in a WBDO was 253 (35 median) and 156 (11 median) for surface water and groundwater systems, respectively. Surface water in general, caused larger outbreaks than groundwater systems and this most likely reflects that the larger waterworks in Norway use surface water as their source. Of the 102 outbreaks, the etiologic agent was identified in 60. Campylobacter and Norovirus were the most frequently identified causative agents of total outbreaks (26 and 19, respectively), whereas Norovirus and Giardia caused most of the disease cases (42% and 21%, respectively). Norovirus caused the same number of outbreaks in Norwegian groundwater systems as in surface water systems, even though groundwater is delivered from relatively fewer drinking water supply systems. Parasites were not identified in outbreaks associated with groundwater systems. Two outbreaks associated with parasites occurred in surface water systems and one of these affected 4,000-6,000 people and is the largest WBDO registered in Norway.

The two largest Norovirus outbreaks (350 and 800 persons) both occurred during the winter season (December and January). This may be due to the fact that Norovirus is more frequently found in Norwegian raw sewage during the cold season (October-March) than in summer (April-September) and therefore the risk of contamination of water systems is increased during winter. Also groundwater in Norway has a temperature of 2-7 degrees C, which is more conducive to virus persistence than higher temperatures. All of the Campylobacter outbreaks occurred during March to November, with a peak in July-September. This peak is associated with the occurrence of coliforms in Norwegian groundwater in bedrock wells and the period of manure spreading in Norway. Birds and animals carrying Campylobacter were associated with five of the Campylobacter outbreaks reported in surface water systems.

Disinfection is not used in 55% of the community groundwater works and most of the individual groundwater supplies in Norway. Of the community surface waterworks, 12% do not disinfect the water. The most common deficiency in Norwegian drinking water systems during 1984-2007 was the use of untreated surface water (27% of all outbreaks) and groundwater (26% of all outbreaks), which caused 15% and 14%, respectively, of all disease cases. Most of these outbreaks were found to occur in individual groundwater systems and community surface water systems. No outbreaks were reported as a result of disinfection deficiencies (failure of disinfection in a supply that was normally disinfected) in groundwater systems, however in surface water systems, disinfection deficiencies caused 42% of the outbreaks, and caused by far the highest proportion of disease cases in surface water systems (61%). In all of the nine disinfection deficiency outbreaks, a temporary failure in chlorination was the cause. Nine of the outbreaks were caused by distribution system deficiencies, three of which occurred in communities supplied by groundwater and six by surface water. The three groundwater system outbreaks caused by distribution system deficiencies represented 55% of the total number of reported disease cases in groundwater systems.

Additional surveillance of both individual and community groundwater supply systems is needed in order to prevent outbreaks from occurring in these systems. Direct contamination in the well and infiltration of sewage are both major reasons for groundwater contamination. When groundwater is supplied without disinfection, source protection is important so public health is not at risk. If groundwater is influenced by contaminated surface water or if regulations for detention times (currently 60 days transport time in the saturated zone) are not met, then adequate disinfection needs to be provided. As Norovirus was found to be of importance as a disease causing agent in groundwater systems, the regulations for source protection and treatment requirements for groundwater systems may need to be reconsidered to ensure drinking water quality with respect to viruses in particular. When reporting waterborne outbreaks, information on the type of aquifer and protection zones should be included in order to improve the regulations regarding groundwater systems.

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