Quantitative microbiological risk assessment; new tools to assess and manage risksfrom pathogens in drinking water

摘要

In Canada and other industrialized nations, a combination of guidelines, regulations andgood management practices help ensure that the risk of contracting infectious diseasefrom drinking water is very low. Despite this, outbreaks of waterborne gastroenteritishave occurred, even in the absence of bacteriological indicators. Quantitative microbialrisk assessment (QMRA) tools applied to drinking water offer a risk-based approach tounderstanding how drinking water treatment barriers, and interactions between them, mayimpact human health risk from pathogens.Health Canada and Decisionalysis Risk Consultants Inc. have developed a probabilisticmodel that estimates the level of risk to human health from exposure to index pathogensin treated drinking water. The model explores the impact of water treatment upon theburden of disease associated with pathogens found in drinking water, namelyCryptosporidium parvum, Giardia lamblia, Rotavirus, and pathogenic Escherichia coli.The primary estimates produced by the model are: (i) the reduction in pathogen levels asa result of treatment barriers, (ii) the expected number of illnesses per year from thereference pathogens in treated drinking water, and (iii) the disease burden attributable tothe treated drinking water. To illustrate the use of the tool, data from the City of Ottawais used to estimate the impact of a number of current and future treatment scenarios onthe risk of waterborne disease. Results are used to compare the relative importance ofmultiple treatment barriers during optimal and non-optimal operating conditions. Resultsare also used to determine optimum treatment targets for primary disinfection. TheQMRA model provides a framework for understanding the nature of microbial risk in adrinking water supply system, and can be used to evaluate the impact of changes in watertreatment on population health risk.