Retrospective Surveillance for Drinking Water-Related Illnesses in Canada

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Waterborne infections are an important cause of preventable enteric disease. This report obtained information on: characteristics of waterborne disease events (WBEs) in Canada; factors contributing to WBEs; current WBE detection and prevention practices; and, information needs of front-line public health staff.

Forty-seven WBEs were identified, the majority occurring prior to 2001. Giardia and Cryptosporidium were the most common etiological agents, followed by bacteria and viruses. Half of the communities experiencing WBEs had surface water source, mostly from unprotected watersheds. No water treatment was available for 39% of the communities, disinfection alone was used in 46%, and filtration combined with disinfection was used in 15%. Communities with larger populations tended to use a multiple barrier approach. Most regions issued some form of boil order or advisory in response to the outbreak. The proportion of regions using surface water declined post-outbreak while water treatment practices tended to improve. The majority of WBEs occurred in small to medium-sized population communities with the exception of those caused by Cryptosporidium, which occurred mainly in larger communities. For the most part, Giardia, bacteria and viruses were the etiologic agents that occurred in communities having either no water treatment or disinfection only. Cryptosporidium-related outbreaks generally occurred in communities having some combination of disinfection and filtration (WBEs related to systems which were either old or had system failure). Approximately 50% of communities experiencing WBEs did not monitor water quality. Regions often cited multiple factors; such as, inadequate treatment, lack of source protection, and precipitation. In response to outbreaks, 65% of regions changed the water source, 56% upgraded or changed the treatment system, and 30% changed or improved policy, reporting, monitoring, or a combination thereof.

Key opportunities to improve drinking water management and mitigate known risks for waterborne disease and WBEs include: improve water treatment effectiveness and water quality monitoring; enhance waterborne disease surveillance and communication between stakeholders; establish WBE prevention plans and policies that include watershed management and which take into account the potential for extreme weather events and the impact of global climate change; seek appropriate expert advice in the event of WBEs; and, place special emphasis on small to medium-sized communities with regard to all these opportunities. In addition, collection and dissemination of information on WBEs should be encouraged.

Publication Date Aug 20, 2009
Author Wilson J, Aramini J, Clarke S, Novotny M, Quist M, Keegan V
Posted by NCCEH Dec 11, 2010