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The incidence of infectious waterborne disease in Canada continues to be a public health issue and can be associated with the source of drinking water. Millions of Canadians relying on unregulated private well water are at increased risk of disease. This study examined relationships between well and owner characteristics and the frequency of microbial testing of private wells in two southern-Ontario counties. Using multi-level logistic regression models, testing frequency (i.e., at least once per year vs. less) was modeled, as both self-reported and laboratory-validated, for associations with owner and well characteristics. For the self-reported outcome, a previous adverse test result significantly increased the odds of being classified as a frequent tester, and owners with a well-head more than 16 inches (40.6 cm) above the ground were at significantly higher odds of being classified as frequent testers compared to those with well-heads less than 16 inches above the ground and those below ground level. For the model based on the laboratory-validated outcome, the odds of an owner being a frequent tester significantly varied with the length of occupancy and the occurrence of a previous adverse result. The absence of associations between other well characteristics and testing frequency suggests that well safety education could benefit these communities.

Intestinal enterococci indicate the fecal contamination of bathing waters. This study defines the performance characteristics of the reference method ISO 7899-2:2000 with water samples collected from inland and coastal bathing areas in Finland. From a total of 341 bacterial isolates grown on Slanetz and Bartley medium, 63.6% were confirmed as intestinal enterococci on bile aesculin agar. The partial 16S rRNA gene sequences showed that Enterococcus faecium and Enterococcus faecalis clades accounted for 93.1% of the confirmed isolates. The range of the false positive and false negative rate of the ISO 7899-2 was 0.0-18.5% and 5.6-57.1%, respectively, being affected by the presumptive colony count on the membrane. The analysis of multiple sample volumes is proposed to reach 10-100 colonies per membrane when 47 mm diameter membranes are used to prevent overestimation of low counts and underestimation of the high counts.

The health-based targets of 1 in 10,000 for infection and 10(-6) disability adjusted life years (DALYs) per person per year are increasingly being considered, or have already been adopted, to define microbial safety targets for water. The aim of this paper is to convey information about how these two targets compare by converting each of the target values to a common metric. The metric chosen for viral (rotavirus and norovirus) and protozoan (Cryptosporidium) reference pathogens is the estimated maximum number of annual drinking water-associated cases of acute diarrhoeal disease tolerated. For the reference bacterial pathogen Campylobacter, sequelae to acute diarrhoeal illness have also been considered in estimating the tolerable number of cases for the DALY target. Also investigated is whether non-compliance with targets would be detected as a waterborne disease outbreak by the health surveillance system in an extreme hypothetical situation whereby all tolerable cases per annum occurred as a single event. The paper highlights that verification of compliance with targets cannot be demonstrated by the absence of reported drinking water-associated outbreaks alone and concludes that introduction of a quantitative health-based outcome for drinking water in Australia would help improve water quality management by providing a common goal directly linked to health outcomes.

In recent decades, more than 2 billion people have gained access to improved drinking water sources thanks to extensive effort from governments, and public and private sector entities. Despite this progress, many water sector development interventions do not provide access to safe water or fail to be sustained for long-term use. The authors examined drinking water quality of previously implemented water improvement projects in three communities in western Kenya and three communities in southern Vietnam. The cross-sectional study of 219 households included measurements of viable Escherichia coli. High rates of E. coli prevalence in these improved water sources were found in many of the samples. These findings suggest that measures above and beyond the traditional 'improved source' definition may be necessary to ensure truly safe water throughout these regions.

The MI agar, Colilert(®), Chromocult coliform(®) agar, and DC with BCIG agar chromogenic culture-based methods used to assess microbiological quality of drinking water were compared in terms of their ubiquity, sensitivity, ease of use, growth of atypical colonies and affordability. For ubiquity, 129 total coliform (representing 76 species) and 19 Escherichia coli strains were tested. Then, 635 1-L well water samples were divided into 100 mL subsamples for testing by all four methods. Test results showed that 70.5, 52.7, 36.4, and 23.3% of the non-E. coli total coliform strains and 94.7, 94.7, 89.5, and 89.5% of the 19 E. coli strains yielded a positive signal with the four methods, respectively. They also yielded a total coliform positive signal for 66.5, 51.7, 64.9, and 55.0% and an E. coli positive signal for 16.1, 14.8, 17.3, and 13.4% of the 635 well water samples tested, respectively. Results showed that Colilert(®) is the most expensive method tested in terms of reactants, yet it is the easiest to use. Large numbers of atypical colonies were also often observed on Chromocult coliform(®) and DC with BCIG, thereby challenging the target microorganism count. Thus, the MI agar method seems to be the best option for the assessment of drinking water quality.

The last century has been marked by major advances in the understanding of microbial disease risks from water supplies and significant changes in expectations of drinking water safety. The focus of drinking water quality regulation has moved progressively from simple prevention of detectable waterborne outbreaks towards adoption of health-based targets that aim to reduce infection and disease to a level well below detection limits at the community level. This review outlines the changes in understanding of community disease and waterborne risks that prompted development of these targets, and also describes their underlying assumptions and current context. Issues regarding the appropriateness of selected target values, and how continuing changes in knowledge and practice may influence their evolution, are also discussed.

Water is critical for life, but many people do not have access to clean and safe drinking water and die because of waterborne diseases. The analysis of drinking water for the presence of indicator microorganisms is key to determining microbiological quality and public health safety. However, drinking water-related illness outbreaks are still occurring worldwide. Moreover, different indicator microorganisms are being used in different countries as a tool for the microbiological examination of drinking water. Therefore, it becomes very important to understand the potentials and limitations of indicator microorganisms before implementing the guidelines and regulations designed by various regulatory agencies. This review provides updated information on traditional and alternative indicator microorganisms with merits and demerits in view of their role in managing the waterborne health risks as well as conventional and molecular methods proposed for monitoring of indicator and pathogenic microorganisms in the water environment. Further, the World Health Organization (WHO) water safety plan is emphasized in order to develop the better approaches designed to meet the requirements of safe drinking water supply for all mankind, which is one of the major challenges of the 21st century.

Concerns about photodegradation products leaching from plastic bottle material into water during solar water disinfection (SODIS) are a major psychological barrier to increased uptake of SODIS. In this study, a comparison of SODIS efficacy using glass and plastic polyethylene terephalate (PET) bottles was carried out under strong real sunlight and overcast weather conditions at Makerere University in central Uganda. Both clear and turbid natural water samples from shallow wells and open dug wells, respectively, were used. Efficacy was determined from the inactivation of a wild strain of Escherichia coli in solar-exposed contaminated water in both glass and PET bottles. The studies reveal no significant difference in SODIS inactivation between glass and PET bottles (95% CI, p > 0.05), for all water samples under the different weather conditions except for clear water under overcast conditions where there was a small but significant difference (95% CI, p = 0.047) with less viable bacterial counts in PET bottles at two intermediate time points but not at the end of the exposure. The results demonstrate that SODIS efficacy in glass under tropical field conditions is comparable to PET plastic. SODIS users in these regions can choose either of reactors depending on availability and preference of the user.

Traditional reservoirs for water storage are important systems of water supply in rural areas of Morocco. These reservoirs are fed by rainwater and/or directly from rivers through open channels; the stored water is used without any treatment as drinking water by the surrounding population. The present study aimed to assess the physicochemical and bacteriological quality of stored water and the corresponding sediment in six traditional reservoirs (R1 to R6) located in the rural municipality of Assif El Mal. We tested two inexpensive methods of disinfecting the stored water: chlorination and solar disinfection in bottles. The results show a rise of organic and mineral concentrations. Regarding bacteriological quality, a critical contamination level was detected (8 × 10(5) CFU/100 ml in water and 9 × 10(7) CFU/g in sediment) according to the 2002 Moroccan Standards for drinking water (0 CFU/100 ml). In the disinfection tests, chlorine disinfection removed all studied germs after just 1 hour, and the solar exposure process removed the majority of bacteria (after 3 hours) except those with a resistant form (Clostridia).

Sewage discharge is considered to be the main source of virus contamination in aquatic environments. There is no correlation between the presence of viruses and the presence of fecal coliforms in water; therefore virological markers are needed when monitoring contamination. This study investigates DNA and RNA virus concentrations in wastewater and evaluates a potential virus marker of human contamination. Influent and effluent samples were collected twice a month throughout a 1-year period. Viruses were detected using quantitative polymerase chain reaction protocols; nucleotide sequencing was carried out for virus genotyping. Human adenovirus (HAdV) and polyomavirus JC (JCPyV) were the most prevalent viruses found in influent samples (100%) with a virus load that ranged from 10(6) to 10(5) genome copies per liter (gc l(-1)). Norovirus genogroup II (NoV GII) and human astrovirus (HAstV) were less prevalent, and ranged from 10(4) to 10(3)gc l(-1). Quantitative data on virus profiles in wastewaters stress the high level of rotavirus species A environmental dissemination and address the potential of HAdV as a useful virological marker of virus contamination in aquatic environments. This study corroborates other studies performed in developed countries on DNA viruses as good markers of human fecal contamination.

A sustainable and low-cost point-of-use household drinking water solar disinfection (SODIS) technology was successfully applied to treat microbiologically contaminated water. Field experiments were conducted to determine the efficiency of SODIS and evaluate the potential benefits and limitations of SODIS under local climatic conditions in Karachi, Pakistan. In order to enhance the efficiency of SODIS, the application of physical interventions were also investigated. Twenty per cent of the total samples met drinking water guidelines under strong sunlight weather conditions, showing that SODIS is effective for complete disinfection under specific conditions. Physical interventions, including black-backed and reflecting rear surfaces in the batch reactors, enhanced SODIS performance. Microbial regrowth was also investigated and found to be more controlled in reactors with reflective and black-backed surfaces. The transfer of plasticizer di(2-ethylhexyl)phthalate (DEHP) released from the bottle material polyethylene terephthalate (PET) under SODIS conditions was also investigated. The maximum DEHP concentration in SODIS-treated water was 0.38 μg/L less than the value of 0.71 μg/L reported in a previous study and well below the WHO drinking-quality guideline value. Thus SODIS-treated water can successfully be used by the people living in squatter settlements of mega-cities, such as Karachi, with some limitations.

In this paper we present a comparative assessment of drinking-water standards from almost all South American countries, using the USA and the Canadian standards and the World Health Organization (WHO) Guidelines as references. Similarities and discrepancies between standards/guidelines were identified through descriptive analyses and, in the case of chemical standards, clustering techniques. In general, one or another of the four consecutive editions of the WHO Guidelines were shown to be quite influential in setting drinking-water standards in the region, but not so much the USA and the Canadian standards. Considerable discrepancies between South American drinking-water standards were found, mainly with respect to chemical substances. Questions are raised about their scientific basis and/or the practicalities for their enforcement. In conclusion, the paper highlights that many drinking-water regulations in South America need updating, taking on the approach of health-based targets in setting these standards, as well as that of a broader risk-based preventive management in the entire supply system to assure water safety.

The Gulf of Mexico Alliance (GOMA) was tasked by the five Gulf State Governors to identify major issues affecting the Gulf of Mexico (GoM) and to set priorities for ameliorating these problems. One priority identified by GOMA is the need to improve detection methods for water quality indicators, pathogens and microbial source tracking. The United States Environmental Protection Agency (USEPA) is tasked with revising water quality criteria by 2012; however, the locations traditionally studied by the USEPA are not representative of the GoM and this has raised concern about whether or not the new criteria will be appropriate. This paper outlines a number of concerns, including deadlines associated with the USEPA Consent Decree, which may prevent inclusion of research needed to produce a well-developed set of methods and criteria appropriate for all regulated waters. GOMA makes several recommendations including ensuring that criteria formulation use data that include GoM-specific conditions (e.g. lower bather density, nonpoint sources), that rapid-testing methods be feasible and adequately controlled, and that USEPA maintains investments in water quality research once the new criteria are promulgated in order to assure that outstanding scientific questions are addressed and that scientifically defensible criteria are achieved for the GoM and other regulated waterbodies.

The microbiological quality of 75 private drinking water supply boreholes in Co. Cork, Ireland was assessed in order to determine the incidence of contamination and the potential pathways of such contamination. Microbiological analysis was carried out using the membrane filtration technique for the recovery of thermotolerant (faecal) coliforms. The sanitary protection of the supplies was evaluated by means of systematic inspections and subsequent qualitative sanitary risk assessment. Almost a quarter of all supplies investigated (24%, n = 18) was found positive for thermotolerant coliforms. Weather conditions had a significant impact on microbiological water quality, increasing both contamination incidence and gross contamination frequency. Over half of the supplies had nine or more sanitary hazards and most had rudimentary sanitary protection measures at the head of the borehole. These low sanitary protection measures suggest that boreholes can pose a significant hazard to valuable groundwater resources by providing direct contamination routes.

Escherichia coli are often used as faecal indicator bacteria (FIB) to provide a measure of microbial pollution in recreational and shellfish harvesting waters. However, although model forecasts for predicting the concentrations of FIB in surface waters are becoming more robust, they suffer from an inconsistency in quantification methods and an understanding of the spatial variation of FIB within a water course. The aim of this study was to investigate the transverse spatial variation in E. coli numbers (as an indicator of faecal pollution) across the estuary of the River Conwy, UK. Water samples were collected from four transverse transects across the estuary. Spatial variation of E. coli was significantly different from one side of the river to the other, although was not correlated with depth or the physiochemical properties of the water. Subsequently, microbial water quality classifications on the two opposite banks suggested very different levels of pollution coming down the river. This work has shown that the side of the river that routine water monitoring samples are taken from can make a significant difference to the classification of microbial water quality. This has important implications for sampling strategies and the use of microbial source tracking (MST) techniques.

The retention and release of total coliforms and Escherichia coli was investigated in hand-pumps removed from tubewells tapping a faecally contaminated aquifer in Matlab, Bangladesh, and from a new hand-pump deliberately spiked with E. coli. All hand-pumps were connected to reservoirs of sterile water and flushed. Faecal coliforms were observed in the discharge from all three of the previously used hand-pumps, at concentrations comparable to levels measured in discharge when they were attached to the tubewells. During daily flushing of one of the previously used hand-pumps, the concentration of total coliforms in the discharge remained relatively constant (approximately 10³ MPN/100 mL). Concentrations of E. coli in the pump discharge declined over time, but E. coli was still detectable up to 29 days after the start of flushing. In the deliberately spiked hand-pump, E. coli was observed in the discharge over 125 days (t₅₀ = 8 days) and found to attach preferentially to elastomeric materials within the hand-pump. Attempts to disinfect both the village and new hand-pumps using shock chlorination were shown to be unsuccessful. These results demonstrate that hand-pumps can act as persistent reservoirs for microbial indicator bacteria. This could potentially influence drinking water quality and bias testing of water quality.

In developing countries, the burden of diarrhoea is still enormous. One way to reduce transmission of pathogens is by water quality interventions. Solar water disinfection (SODIS) is a low-cost and simple method to improve drinking water quality on household level. This paper evaluates the implementation of SODIS in slum areas of Yaoundé, Cameroon. Promoters trained 2,911 households in the use of SODIS. Two surveys with randomly selected households were conducted before (N=2,193) and after (N=783) the intervention. Using a questionnaire, interviewers collected information on the health status of children under five, on liquid consumption, hygiene and other issues. Prior to the intervention, diarrhoea prevalence amounted to 34.3% among children. After the intervention, it remained stable in the control group (31.8%) but dropped to 22.8% in the intervention group. Households fully complying with the intervention exhibited even less diarrhoea prevalence (18.3%) and diarrhoea risk could be reduced by 42.5%. Multivariate analyses revealed that the intervention effects are also observed when other diarrhoea risk factors, such as hygiene and cleanliness of household surroundings, are considered. According to the data, adoption of the method was associated with marital status. Findings suggest health benefits from SODIS use. Further promotional activities in low-income settings are recommended.

Contamination of the nearshore marine environment contributes to a high burden of illness among recreational bathers. Disease surveillance activities carried out by local, state, and territorial agencies in the United States are at present voluntary and passive. Several gaps in the existing regulatory framework for beach management and public health protection are highlighted in this paper. The need for disease surveillance of marine bathers is established. A demonstration is made of how surveillance activities can be used to guide risk management and gauge the effectiveness of current water contact standards. Recommendations are offered for agencies to improve surveillance and protect public health. A foundation is presented on which to develop a model marine health code.

The United States Environmental Protection Agency is committed to developing new recreational water quality criteria for coastal waters by 2012 to provide increased protection to swimmers. We review the uncertainties and shortcomings of the current recreational water quality criteria, describe critical research needs for the development of new criteria, as well as recommend a path forward for new criteria development. We believe that among the most needed research needs are the completion of epidemiology studies in tropical waters and in waters adversely impacted by urban runoff and animal feces, as well as studies aimed to validate the use of models for indicator and pathogen concentration and health risk predictions.

In July 2007, a study by the Centre for Environmental Health Engineering, at the University of Surrey, assessed a modified method of jerry can cleaning in an internally displaced persons (IDP) camp in Kitgum, N. Uganda. The poor condition of drinking water vessels used in the camp was confirmed as a potential source for microbiological contamination both visually and by microbiological testing. Jerry cans were disinfected using high strength sodium hypochlorite (NaOCl) generated using an experimental AquaChlor Solar unit. The study suggested that regular jerry can cleaning, using a high strength chlorine based disinfectant, offers an effective method of alleviating the adverse effects of contamination in water collection and storage vessels. Results indicated that the method is capable of significantly reducing thermo-tolerant coliform numbers to below 5 cfu/100 ml in most cases. Chlorine strength depletion after repetitive cleaning confirms the impact of process. The method does not substitute for good hygiene practices, which are essential for maintaining water quality in the household. It is suggested that the process can play an important role during outbreaks of water-borne diseases, such as cholera, particularly if combined with regular water disinfection., (Copyright IWA Publishing 2008.)

A key objective of the Good Agricultural Practices (GAP) program is to reduce the potential for produce to become contaminated with microbial pathogens, such as through irrigation water. Without microbial standards, however, it is impractical to decide whether there is a need to disinfect, a need to institute watershed protection programs, or a need to institute post-harvest disinfection regimes. To develop such standards, quantitative microbial risk assessments can be performed using pathogen monitoring data for produce. This paper presents an approach which can be used towards the application of a risk assessment framework to developing microbial standards for fresh produce. Risks of infection are estimated using typical monitoring data of Salmonella detected on carrots and assuming various scenarios of the likelihood of an individual consuming a contaminated serving of carrots in a given year. Estimated annual risks of infection range from 2.20 x 10(-5) to 2.16 x 10(-3), assuming 1% and 100% of an individual's carrot servings are contaminated, respectively. In addition, critical factors are identified which need to be incorporated in such a risk assessment approach as well as their impact on risk estimates to provide growers with benchmarks which may be targeted to reduce health risks.

Quantitative microbial risk assessment (QMRA) is increasingly applied to estimate drinking water safety. In QMRA the risk of infection is calculated from pathogen concentrations in drinking water, water consumption and dose response relations. Pathogen concentrations in drinking water are generally low and monitoring provides little information for QMRA. Therefore pathogen concentrations are monitored in the raw water and reduction of pathogens by treatment is modelled stochastically with Monte Carlo simulations. The method was tested in a case study with Campylobacter monitoring data of rapid sand filtration and ozonation processes. This study showed that the currently applied method did not predict the monitoring data used for validation. Consequently the risk of infection was over estimated by one order of magnitude. An improved method for model validation was developed. It combines non-parametric bootstrapping with statistical extrapolation to rare events. Evaluation of the treatment model was improved by presenting monitoring data and modelling results in CCDF graphs, which focus on the occurrence of rare events. Apart from calculating the yearly average risk of infection, the model results were presented in FN curves. This allowed for evaluation of both the distribution of risk and the uncertainty associated with the assessment.

In early 2003, after a prolonged drought period, extensive bushfires occurred in the east of Victoria affecting 1.5 million hectares of land. At the time, smoke and ash from bushfires, settling on roofs, contained pollutants that could potentially contaminate rainwater collected and stored in tanks for domestic use. The major concerns include polycyclic aromatic hydrocarbons (PAHs) from incomplete combustion of organic matter and arsenic from burnt copper chrome arsenate (CCA) treated wood. An increase in microbial contamination through altered nutrient levels was also hypothesised. A pilot study of 49 rainwater tank owners was undertaken in north-east Victoria. A rainwater tank sample was taken and analysed for a variety of parameters including organic compounds, microbiological indicators, metals, nutrients and physico-chemical parameters. A survey was administered concurrently. A number of results were outside the Australian Drinking Water Guideline (ADWG) values for metals and microbiological indicator organisms, but not for any tested organic compounds. PAHs and arsenic are unlikely to be elevated in rainwater tanks as a result of bushfires, but cadmium may be of concern.

Cryptosporidium is a protozoan parasite found in surface waters throughout the United States. Waterborne cryptosporidiosis outbreaks may be associated with contaminated drinking water supplies. The approved method, USEPA (United States Environmental Protection Agency) Method 1623, for testing for the presence of Cryptosporidium in United States surface waters has several limitations. Firstly, recovery efficiency varies widely. Secondly, Method 1623 does not specify a mechanism for assessing the viability and infectivity of oocysts detected, or the Cryptosporidium species of the oocysts. Lastly, there are logistical limitations which are relevant to Method 1623 in particular, and to the state of the science of Cryptosporidium testing in general. Methods that give specific results more quickly, with higher recoveries and better consistency must be developed and made accessible for utilities to use. Improved Cryptosporidium testing methods can minimize uncertainty; this, in turn, will simplify the risk communication task, and the level of trust which the public has in the water utility can be maintained and improved. This paper reviews the current and ongoing research on analytical, monitoring, and sampling methods for Cryptosporidium, and identifies the needs that should be considered in future research.

A workshop was held in Atlanta on July 7-8, 2005, to evaluate the epidemiologic and other information available for estimating endemic waterborne illness risks in the United States. Each paper written for this special issue was discussed and fourteen recommendations were made based on the discussion. In addition, seven major data gaps were identified as being key to reducing the uncertainty associated with a calculation of a national estimate. This summary is provided to help regulatory officials, public health professionals, and others better understand the health measures being estimated and adequacy of the current risk information. The summary also provides a blueprint for researchers interested in studying the endemic and epidemic risks of microbes in drinking water.

The nature and magnitude of endemic waterborne disease are not well characterized in the United States. Epidemiologic studies of various designs can provide an estimate of the waterborne attributable risk along with other types of information. Community drinking water systems frequently improve their operations and may change drinking water treatment and their major source of water. In the United States, many of these treatment changes are the result of regulations promulgated under the Safe Drinking Water Act. A community-intervention study design takes advantage of these "natural" experiments to assess changes in health risks. In this paper, we review the community-intervention studies that have assessed changes in waterborne gastroenteritis risks among immunocompetent populations in industrialized countries. Published results are available from two studies in Australia, one study in the United Kingdom, and one study in the United States. Preliminary results from two other US studies are also available. Although the current information is limited, the risks reported in these community-intervention studies can help inform the national estimate of endemic waterborne gastroenteritis. Information is provided about endemic waterborne risks for unfiltered surface water sources and a groundwater under the influence of surface water. Community-intervention studies with recommended study modifications should be conducted to better estimate the benefits associated with improved drinking water treatment.

Regulations are one of the primary drivers for research on contaminants in drinking water in the United States. Since the original Safe Drinking Water Act (SDWA), enacted in 1974, the United States Environmental Protection Agency (USEPA) has developed a series of drinking water regulations. These regulations are focused on protecting public health. When evaluating available information on whether or not to regulate a constituent in drinking water, USEPA considers available information on health effects and occurrence of the constituent. The authors provide their view of the research needed for these contaminants. For inorganics, more data are needed on perchlorate. For organics, greater treatment and health effects information is warranted for N-nitrosodimethylamine (NDMA), methyl tertiary butyl ether (MTBE) and pharmaceuticals and personal care products. Finally, more research is needed on analytical methods for noroviruses and other emerging pathogens.

The 1996 Safe Drinking Water Act amendments require the US Environmental Protection Agency and the Centers for Disease Control and Prevention to develop a national estimate of the occurrence of waterborne infectious disease that is attributable to public drinking water systems in the United States. Much of the information for developing the national estimate will be derived from epidemiologic data, and the primary outcome of this effort will be an estimate of the number of cases of gastrointestinal illness. While quantifying the number of these cases provides some measure of waterborne disease impact, the usefulness of this measure may be limited because the full spectrum of societal impact also involves consideration of the additional effects of these diseases such as hospitalization costs and lost productivity. If decision-makers wish to compare the impact of waterborne infectious diseases to the impact of some other public health concern (e.g. to aid in resource allocation decisions), then a comparison of case numbers may prove inadequate. Case numbers alone do not provide sufficient information about the severity of different illnesses. Society may value the avoidance of a few cases of severely debilitating illness more than it values the avoidance of many cases of mild illness. In order to compare disparate public health concerns, "burden of disease" measures that incorporate indicators of disease severity, costs, or societal values may prove essential for some types of decisions. We describe epidemiologic measures of severity, quality adjusted life years (QALYs), disability adjusted life years (DALYs), willingness-to-pay, and cost-of-illness methods commonly used for burden of disease estimates, and discuss how some of these summary measures of burden might be used for waterborne disease estimates.

In this paper, the US Environmental Protection Agency (EPA) presents an approach and a national estimate of drinking water related endemic acute gastrointestinal illness (AGI) that uses information from epidemiologic studies. There have been a limited number of epidemiologic studies that have measured waterborne disease occurrence in the United States. For this analysis, we assume that certain unknown incidence of AGI in each public drinking water system is due to drinking water and that a statistical distribution of the different incidence rates for the population served by each system can be estimated to inform a mean national estimate of AGI illness due to drinking water. Data from public water systems suggest that the incidence rate of AGI due to drinking water may vary by several orders of magnitude. In addition, data from epidemiologic studies show AGI incidence due to drinking water ranging from essentially none (or less than the study detection level) to a rate of 0.26 cases per person-year. Considering these two perspectives collectively, and associated uncertainties, EPA has developed an analytical approach and model for generating a national estimate of annual AGI illness due to drinking water. EPA developed a national estimate of waterborne disease to address, in part, the 1996 Safe Drinking Water Act Amendments. The national estimate uses best available science, but also recognizes gaps in the data to support some of the model assumptions and uncertainties in the estimate. Based on the model presented, EPA estimates a mean incidence of AGI attributable to drinking water of 0.06 cases per year (with a 95% credible interval of 0.02-0.12). The mean estimate represents approximately 8.5% of cases of AGI illness due to all causes among the population served by community water systems. The estimated incidence translates to 16.4 million cases/year among the same population. The estimate illustrates the potential usefulness and challenges of the approach, and provides a focus for discussions of data needs and future study designs. Areas of major uncertainty that currently limit the usefulness of the approach are discussed in the context of the estimate analysis.

Microbial risk assessment (MRA) evaluates the likelihood of adverse human health effects that occur following exposure to pathogenic microorganisms. This paper focuses on the potential use of MRA to provide insight to the national estimate of acute gastrointestinal illness (AGI) in the United States among persons served by public water systems. This article defines MRA, describes how MRA is implemented, provides an overview of the field of MRA and discusses how MRA may be useful for characterizing the national estimate. Communities served by drinking water systems with relatively contaminated source waters, sub-standard treatment facilities, and/or contamination problems in their distribution systems are subject to higher risks than communities where such issues are less of a concern. Further, the risk of illness attributable to pathogens in drinking water in each community can be thought of as the sum of the risk from the treated drinking water and the risk from the distribution system. Pathogen-specific MRAS could be developed to characterize the risk associated with each of these components; however, these assessments are likely to under-estimate the total risk from all pathogens attributable to drinking water. Potential methods for developing such MRAs are discussed along with their associated limitations.