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

摘要

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