Infectious disease outbreaks related to drinking water in Canada , 1974-2001.

Schuster, C.J., Ellis, A.G., Robertson, W.J., Charron, D.F., Aramini, J.J., Marshall , B.J. and Medeiros, D.T. (2005) Canadian Journal of Public Health, 94 (4); 254-58.

Information on waterborne outbreaks in Canada from 1974-2001 was analysed with the objective of identifying apparent trends, reviewing the current status of monitoring and reporting, and to gain a better understanding of the impact of drinking water quality on public health and disease burden.

Data on outbreaks was obtained from two main sources: Health Canada 's summary reports and the Quebec health reports. This was supplemented by an extensive literature review. Outbreaks were categorised as being definitely, probably or possibly waterborne in nature. The data was also categorized by water supply type: public (municipal), semi-public (privately owned systems providing drinking water to the visiting general public), and private (systems providing drinking water to the individuals owning the system and their guests). Data was also gathered on the water system or the location of the outbreak. Information on the agent responsible for the outbreak was collected from original documentation.

There were 288 outbreaks of disease linked to a drinking water source in the final data set. Nearly half of the outbreaks were reported in semi-public systems (138 outbreaks), 99 were in public water systems and 51 were in private systems. Over one third of the outbreaks were categorised as definitely waterborne. Of these outbreaks most were in public systems. The highest number of outbreaks annually was during the period 1989 to 1996.

For 134 of the outbreaks, the pathogen responsible was not known. Of the remaining outbreaks, the most common causative agent was Giardia lamblia (51 outbreaks) followed by Campylobacter (24 outbreaks) and Cryptosporidium , hepatitis A, Norwalk-like viruses and Salmonella (each responsible for 10 or more outbreaks). There was more than one pathogen involved in four of the outbreaks. Most semi-private and private systems did not document a particular pathogen as the source of the outbreak.

There were 223 outbreaks which documented a single contributing factor or circumstance. More than three contributing factors were documented in 9 of the outbreaks. Reasons most frequently stated as contributing to the occurrence of the outbreak included issues with the water treatment process and the need for more stringent or enhanced treatment techniques.

The majority of all outbreaks occurred in spring (between March and May) and summer (between June and August). Spring was the season where meteorological conditions or specific weather events were most often implicated. Several public system outbreaks in summer were attributed at least in part to weather events.

This study found a seasonal distribution of waterborne disease outbreaks in Canada with a peak in spring/summer. Severe weather, close proximity to animal populations, treatment system malfunctions, poor maintenance and treatment practices were all associated with drinking water supply outbreaks. This study found the quality of existing information associated with waterborne disease outbreaks is not adequate, with basic information often missing. The current data could be improved if a nationally standardised surveillance system was implemented and epidemiological training was provided to improve the quality of outbreak investigation information. There is also a need for trend identification and policy development to prevent future outbreaks.