Current assumptions for quantitative microbial risk assessment (QMRA) of Norovirus contamination of drinking water catchments due to recreational activities: an update.

Contamination of drinking water from Norovirus (NoV) and other waterborne viruses is a major public health concern globally. Increasingly, quantitative microbial risk assessment (QMRA) is being used to assess the various risks from waterborne pathogens and evaluate control strategies. As urban populations grow and expand, there is increasing demand for recreational activities in drinking water catchments. QMRA relies on context-specific data to map out the pathways by which viruses can enter water and be transferred to drinking water consumers and identify risk factors and appropriate controls. This review examines the current evidence base and assumptions for QMRA analysis of NoV and other waterborne viral pathogens and recommends numerical values based on the most recent evidence to better understand the health risks associated with recreators in Australian drinking water sources; these are broadly applicable to all drinking water sources where recreational access is allowed. Key issues include the lack of an agreed upon data and dose-response models for human infectious NoV genotypes, faecal shedding by bathers, the extent of NoV infectivity and aggregation, resistance (secretor status) to NoV and the extent of secondary transmission.

Review of generic screening level assumptions for quantitative microbial risk assessment (QMRA) for estimating public health risks from Australian drinking water sources contaminated with Cryptosporidium by recreational activities.

As urban communities continue to grow, demand for recreational access (including swimming) in drinking water sources have increased, yet relatively little is understood about the public health implications this poses for drinking water consumers. Preventative risk-based approaches to catchment management, informed by quantitative microbial risk assessment (QMRA), requires accurate input data to effectively model risks. A sound understanding of the knowledge gaps is also important to comprehend levels of uncertainty and help prioritise research needs. Cryptosporidium is one of the most important causes of waterborne outbreaks of gastroenteritis globally due to its resistance to chlorine. This review was undertaken by Water Research Australia to provide the most up-to-date information on current Cryptosporidium epidemiological data and underlying assumptions for exposure assessment, dose response and risk assessment for generic components of QMRA for Cryptosporidium and highlights priorities for common research. Key interim recommendations and guidelines for numerical values for relatively simple screening level QMRA modelling are provided to help support prospective studies of risks to drinking water consumers from Cryptosporidium due to body-contact recreation in source water. The review does not cover site-specific considerations, such as the levels of activity in the source water, the influence of dilution and inactivation in reservoirs, or water treatment. Although the focus is Australia, the recommendations and numerical values developed in this review, and the highlighted research priorities, are broadly applicable across all drinking source water sources that allow recreational activities.

Development and implementation of water safety plans for small water supplies in Bangladesh: benefits and lessons learned.

Water safety plans (WSPs) are promoted by the WHO as the most effective means of securing drinking water safety. To date most experience with WSPs has been within utility supplies, primarily in developed countries. There has been little documented experience of applying WSPs to small community-managed systems, particularly in developing countries. This paper presents a case study from Bangladesh describing how WSPs can be developed and implemented for small systems. Model WSPs were developed through consultation with key water sector practitioners in the country. Simplified tools were developed to translate the formal WSPs into a format that was meaningful and accessible for communities to use. A series of pilot projects were implemented by Non-Governmental Organisations (NGOs) across the country covering all major water supplies. The results show that WSPs can be developed and implemented for small community managed water supplies and improve the sanitary condition and water quality of water sources. Hygiene behaviour improved and household water quality showed a significant reduction in contamination. Chlorination was found to be important for some technologies, thus increasing the costs of water supply and raising important problems with respect to transfer to the communities. Simple tools for community monitoring were found to be effective in supporting better water safety management.

Disease burden estimation to support policy decision-making and research prioritization for arsenic mitigation.

The main response to arsenic contamination of shallow tubewells in Bangladesh is the provision of alternative water supplies. To support decision-making in relation to alternative water supply selection, the Arsenic Policy Support Unit commissioned the development of a tool for estimating disease burdens for specific options using disability-adjusted life years as the metric. This paper describes the assumptions in dose-responses, relationships between microbial indicators and pathogens, water consumed and population characteristics used, and presents a case study of how the tool was applied. Water quality data and dose-response models were used to predict disease burdens due to microbial pathogens and arsenic. Disease burden estimates predicted by the tool were based on evidence in the published literature. There were uncertainties in key assumptions of water consumed and the ratio of microbial indicators and pathogens, which led to broad confidence intervals and the need to consider the results in a wider context and further research needs. Deep tubewells and rainwater harvesting had the lowest disease burden estimates, while pond sand filters and dug wells had much higher predicted disease burden due to frequent microbial contamination. The need for rigorous water supply protection through water safety plans was highlighted. At present, the risk assessment is useful for informing judgement by experienced water and health professionals and identifying key research questions. Improved arsenic dose-response models and a better understanding of the relationship between microbial indicators and pathogens in tropical settings are required.

Meeting report: Application of genotyping methods to assess risks from cryptosporidium in watersheds.

A workshop titled "Application of Genotyping Methods to Assess Pathogen Risks from Cryptosporidium in Drinking Water Catchments" was held at the International Water Association biennial conference, Marrakech, Morocco, 23 September 2004. The workshop presented and discussed the findings of an interlaboratory trial that compared methods for genotyping Cryptosporidium oocysts isolated from feces. The primary goal of the trial and workshop was to assess the utility of current Cryptosporidium genotyping methods for determining the public health significance of oocysts isolated from feces in potable-water-supply watersheds. An expert panel of 16 watershed managers, public health practitioners, and molecular parasitologists was assembled for the workshop. A subordinate goal of the workshop was to educate watershed management and public health practitioners. An open invitation was extended to all conference delegates to attend the workshop, which drew approximately 50 interested delegates. In this report we summarize the peer consensus emerging from the workshop. Recommendations on the use of current methods by watershed managers and public health practitioners were proposed. Importantly, all the methods that were reported in the trial were mutually supporting and found to be valuable and worthy of further utility and development. Where there were choices as to which method to apply, the small-subunit ribosomal RNA gene was considered to be the optimum genetic locus to target. The single-strand conformational polymorphism method was considered potentially the most valuable for discriminating to the subtype level and where a large number of samples were to be analyzed. A research agenda for protozoan geneticists was proposed to improve the utility of methods into the future. Standardization of methods and nomenclature was promoted.