Onsite Nonpotable Water Systems Pathogen Treatment Targets: A Comparison of Infection and Disability-Adjusted Life Years (DALYs) Risk Benchmark Approaches.

Pathogen log10 reduction targets for onsite nonpotable water systems were calculated using both annual infection (LRTINF) and disability-adjusted life year (LRTDALY) benchmarks. The DALY is a measure of the health burden of a disease, accounting for both the severity and duration of illness. Results were evaluated to identify if treatment requirements change when accounting for the likelihood, duration, and severity of illness in addition to the likelihood of infection. The benchmarks of 10-4 infections per person per year (ppy) and 10-6 DALYs ppy were adopted along with multilevel dose-response models for Norovirus and Campylobacter jejuni, which characterize the probability of illness given infection (Pill|inf) as dose-dependent using challenge or outbreak data. We found differences between treatment requirements, LRTINF - LRTDALY, for some pathogens, driven by the likelihood of illness, rather than the severity of illness. For pathogens with dose-independent Pill|inf characterizations, such as Cryptosporidium spp., Giardia, and Salmonella enterica, the difference, LRTINF - LRTDALY, was identical across reuse scenarios (

Comparison of Predicted Microbiological Human Health Risks Associated with de Facto, Indirect, and Direct Potable Water Reuse.

Increasing interest in recycling water for potable purposes makes understanding the risks associated with potential acute microbial hazards important. We compared risks from de facto reuse, indirect potable reuse (IPR), and direct potable reuse (DPR) scenarios using a previously published quantitative microbial risk assessment methodology and literature review results. The de facto reuse simulation results are compared to a Cryptosporidium spp. database collected for the Long Term 2 Enhanced Surface Water Treatment Rule's information collection rule (ICR) and to a literature review of norovirus (NoV) densities in ambient surface waters. The de facto simulation results with a treated wastewater effluent contribution of 1% in surface waters and a residence time of 30 days most closely match the ICR dataset. The de facto simulations also suggest that using NoV monitoring data from surface waters may overestimate microbial risks, compared to NoV data from raw sewage coupled with wastewater treatment reduction estimates. The predicted risks from IPR and DPR are consistently lower than those for the de facto reuse scenarios assuming the AWTFs are operating within design specifications. These analyses provide insight into the microbial risks associated with various potable reuse scenarios and highlight the need to carefully consider drinking water treatment choices when wastewater effluent is a component of any drinking water supply.

Potable Water Reuse: What Are the Microbiological Risks?

PURPOSE OF REVIEW: With the increasing interest in recycling water for potable reuse purposes, it is important to understand the microbial risks associated with potable reuse. This review focuses on potable reuse systems that use high-level treatment and de facto reuse scenarios that include a quantifiable wastewater effluent component. RECENT FINDINGS: In this article, we summarize the published human health studies related to potable reuse, including both epidemiology studies and quantitative microbial risk assessments (QMRA). Overall, there have been relatively few health-based studies evaluating the microbial risks associated with potable reuse. Several microbial risk assessments focused on risks associated with unplanned (or de facto) reuse, while others evaluated planned potable reuse, such as indirect potable reuse (IPR) or direct potable reuse (DPR). The reported QMRA-based risks for planned potable reuse varied substantially, indicating there is a need for risk assessors to use consistent input parameters and transparent assumptions, so that risk results are easily translated across studies. However, the current results overall indicate that predicted risks associated with planned potable reuse scenarios may be lower than those for de facto reuse scenarios. Overall, there is a clear need to carefully consider water treatment train choices when wastewater is a component of the drinking water supply (whether de facto, IPR, or DPR). More data from full-scale water treatment facilities would be helpful to quantify levels of viruses in raw sewage and reductions across unit treatment processes for both culturable and molecular detection methods.

Direct potable reuse microbial risk assessment methodology: Sensitivity analysis and application to State log credit allocations.

Understanding pathogen risks is a critically important consideration in the design of water treatment, particularly for potable reuse projects. As an extension to our published microbial risk assessment methodology to estimate infection risks associated with Direct Potable Reuse (DPR) treatment train unit process combinations, herein, we (1) provide an updated compilation of pathogen density data in raw wastewater and dose-response models; (2) conduct a series of sensitivity analyses to consider potential risk implications using updated data; (3) evaluate the risks associated with log credit allocations in the United States; and (4) identify reference pathogen reductions needed to consistently meet currently applied benchmark risk levels. Sensitivity analyses illustrated changes in cumulative annual risks estimates, the significance of which depends on the pathogen group driving the risk for a given treatment train. For example, updates to norovirus (NoV) raw wastewater values and use of a NoV dose-response approach, capturing the full range of uncertainty, increased risks associated with one of the treatment trains evaluated, but not the other. Additionally, compared to traditional log-credit allocation approaches, our results indicate that the risk methodology provides more nuanced information about how consistently public health benchmarks are achieved. Our results indicate that viruses need to be reduced by 14 logs or more to consistently achieve currently applied benchmark levels of protection associated with DPR. The refined methodology, updated model inputs, and log credit allocation comparisons will be useful to regulators considering DPR projects and design engineers as they consider which unit treatment processes should be employed for particular projects.

Estimating the probability of illness due to swimming in recreational water with a mixture of human- and gull-associated microbial source tracking markers.

Beaches often receive fecal contamination from more than one source. Human sources include untreated sewage as well as treated wastewater effluent, and animal sources include wildlife such as gulls. Different contamination sources are expected to pose different health risks to swimmers. Genetic microbial source tracking (MST) markers can be used to detect bacteria that are associated with different animal sources, but the health risks associated with a mixture of MST markers are unknown. This study presents a method for predicting these health risks, using human- and gull-associated markers as an example. Quantitative Microbial Risk Assessment (QMRA) is conducted with MST markers as indicators. We find that risks associated with exposure to a specific concentration of a human-associated MST marker (HF) are greater if the HF source is untreated sewage rather than treated wastewater effluent. We also provide a risk-based threshold of HF from untreated sewage at a beach, to stay below a predicted illness risk of 3 per 100 swimmers, that is a function of gull-associated MST marker (CAT) concentration.

Incidence of gastrointestinal illness following wet weather recreational exposures: Harmonization of quantitative microbial risk assessment with an epidemiologic investigation of surfers.

We modeled the risk of gastrointestinal (GI) illness associated with recreational exposures to marine water following storm events in San Diego County, California. We estimated GI illness risks via quantitative microbial risk assessment (QMRA) techniques by consolidating site specific pathogen monitoring data of stormwater, site specific dilution estimates, literature-based water ingestion data, and literature based pathogen dose-response and morbidity information. Our water quality results indicated that human sources of contamination contribute viral and bacterial pathogens to streams draining an urban watershed during wet weather that then enter the ocean and affect nearshore water quality. We evaluated a series of approaches to account for uncertainty in the norovirus dose-response model selection and compared our model results to those from a concurrently conducted epidemiological study that provided empirical estimates for illness risk following ocean exposure. The preferred norovirus dose-response approach yielded median risk estimates for water recreation-associated illness (15 GI illnesses per 1000 recreation events) that closely matched the reported epidemiological results (12 excess GI illnesses per 1000 wet weather recreation events). The results are consistent with norovirus, or other pathogens associated with norovirus, as an important cause of gastrointestinal illness among surfers in this setting. This study demonstrates the applicability of QMRA for recreational water risk estimation, even under wet weather conditions and describes a process that might be useful in developing site-specific water quality criteria in this and other locations.

Human health risk implications of multiple sources of faecal indicator bacteria in a recreational waterbody.

We simulate the influence of multiple sources of enterococci (ENT) as faecal indicator bacteria (FIB) in recreational water bodies on potential human health risk by considering waters impacted by human and animal sources, human and non-pathogenic sources, and animal and non-pathogenic sources. We illustrate that risks vary with the proportion of culturable ENT in water bodies derived from these sources and estimate corresponding ENT densities that yield the same level of health protection that the recreational water quality criteria in the United States seeks (benchmark risk). The benchmark risk is based on epidemiological studies conducted in water bodies predominantly impacted by human faecal sources. The key result is that the risks from mixed sources are driven predominantly by the proportion of the contamination source with the greatest ability to cause human infection (potency), not necessarily the greatest source(s) of FIB. Predicted risks from exposures to mixtures comprised of approximately 30% ENT from human sources were up to 50% lower than the risks expected from purely human sources when contamination is recent and ENT levels are at the current water quality criteria levels (35 CFU 100 mL(-1)). For human/non-pathogenic, human/gull, human/pig, and human/chicken faecal mixtures with relatively low human contribution, the predicted culturable enterococci densities that correspond to the benchmark risk are substantially greater than the current water quality criteria values. These findings are important because they highlight the potential applicability of site specific water quality criteria for waters that are predominantly un-impacted by human sources.

Evaluating the importance of faecal sources in human-impacted waters.

Quantitative microbial risk assessment (QMRA) was used to evaluate the relative contribution of faecal indicators and pathogens when a mixture of human sources impacts a recreational waterbody. The waterbody was assumed to be impacted with a mixture of secondary-treated disinfected municipal wastewater and untreated (or poorly treated) sewage, using Norovirus as the reference pathogen and enterococci as the reference faecal indicator. The contribution made by each source to the total waterbody volume, indicator density, pathogen density, and illness risk was estimated for a number of scenarios that accounted for pathogen and indicator inactivation based on the age of the effluent (source-to-receptor), possible sedimentation of microorganisms, and the addition of a non-pathogenic source of faecal indicators (such as old sediments or an animal population with low occurrence of human-infectious pathogens). The waterbody indicator density was held constant at 35 CFU 100 mL(-1) enterococci to compare results across scenarios. For the combinations evaluated, either the untreated sewage or the non-pathogenic source of faecal indicators dominated the recreational waterbody enterococci density assuming a culture method. In contrast, indicator density assayed by qPCR, pathogen density, and bather gastrointestinal illness risks were largely dominated by secondary disinfected municipal wastewater, with untreated sewage being increasingly less important as the faecal indicator load increased from a non-pathogenic source. The results support the use of a calibrated qPCR total enterococci indicator, compared to a culture-based assay, to index infectious human enteric viruses released in treated human wastewater, and illustrate that the source contributing the majority of risk in a mixture may be overlooked when only assessing faecal indicators by a culture-based method.

Estimating the primary etiologic agents in recreational freshwaters impacted by human sources of faecal contamination.

Epidemiology studies of recreational waters have demonstrated that swimmers exposed to faecally-contaminated recreational waters are at risk of excess gastrointestinal illness. Epidemiology studies provide valuable information on the nature and extent of health effects, the magnitude of risks, and how these risks are modified or associated with levels of faecal contamination and other measures of pollution. However, such studies have not provided information about the specific microbial agents that are responsible for the observed illnesses in swimmers. The objective of this work was to understand more fully the reported epidemiologic results from studies conducted on the Great Lakes in the US during 2003 and 2004 by identifying pathogens that could have caused the observed illnesses in those studies. We used a Quantitative Microbial Risk Assessment (QMRA) approach to estimate the likelihood of pathogen-induced adverse health effects. The reference pathogens used for this analysis were Norovirus, rotavirus, adenovirus, Cryptosporidium spp., Giardia lamblia, Campylobacter jejuni, Salmonella enterica, and Escherichia coli O157:H7. Two QMRA-based approaches were used to estimate the pathogen combinations that would be consistent with observed illness rates: in the first, swimming-associated gastrointestinal (GI) illnesses were assumed to occur in the same proportion as known illnesses in the US due to all non-foodborne sources, and in the second, pathogens were assumed to occur in the recreational waters in the same proportion as they occur in disinfected secondary effluent. The results indicate that human enteric viruses and in particular, Norovirus could have caused the vast majority of the observed swimming-associated GI illnesses during the 2003/2004 water epidemiology studies. Evaluation of the time-to-onset of illness strongly supports the principal finding and sensitivity analyses support the overall trends of the analyses even given their substantial uncertainties.

Estimated human health risks from exposure to recreational waters impacted by human and non-human sources of faecal contamination.

This work was conducted to determine whether estimated risks following exposure to recreational waters impacted by gull, chicken, pig, or cattle faecal contamination are substantially different than those associated with waters impacted by human sources such as treated wastewater. Previously published Quantitative Microbial Risk Assessment (QMRA) methods were employed and extended to meet these objectives. Health outcomes used in the analyses were infection from reference waterborne pathogens via ingestion during recreation and subsequent gastrointestinal (GI) illness. Illness risks from these pathogens were calculated for exposure to faecally contaminated recreational water at the U.S. regulatory limits of 35 cfu 100 mL(-1) enterococci and 126 cfu 100 mL(-1)Escherichia coli. The probabilities of GI illness were calculated using pathogen dose-response relationships from the literature and Monte Carlo simulations. Three scenarios were simulated, representing a range of feasible interpretations of the available data. The primary findings are that: 1) GI illness risks associated with exposure to recreational waters impacted by fresh cattle faeces may not be substantially different from waters impacted by human sources; and 2) the risks associated with exposure to recreational waters impacted by fresh gull, chicken, or pig faeces appear substantially lower than waters impacted by human sources. These results suggest that careful consideration may be needed in the future for the management of recreational waters not impacted by human sources.

Predicting pathogen risks to aid beach management: the real value of quantitative microbial risk assessment (QMRA).

There has been an ongoing dilemma for agencies that set criteria for safe recreational waters in how to provide for a seasonal assessment of a beach site versus guidance for day-to-day management. Typically an overall 'safe' criterion level is derived from epidemiologic studies of sewage-impacted beaches. The decision criterion is based on a percentile value for a single sample or a moving median of a limited number (e.g. five per month) of routine samples, which are reported at least the day after recreator exposure has occurred. The focus of this paper is how to better undertake day-to-day recreational site monitoring and management. Internationally, good examples exist where predictive empirical regression models (based on rainfall, wind speed/direction, etc.) may provide an estimate of the target faecal indicator density for the day of exposure. However, at recreational swimming sites largely impacted by non-sewage sources of faecal indicators, there is concern that the indicator-illness associations derived from studies at sewage-impacted beaches may be inappropriate. Furthermore, some recent epidemiologic evidence supports the relationship to gastrointestinal (GI) illness with qPCR-derived measures of Bacteroidales/Bacteroides spp. as well as more traditional faecal indicators, but we understand less about the environmental fate of these molecular targets and their relationship to bather risk. Modelling pathogens and indicators within a quantitative microbial risk assessment framework is suggested as a way to explore the large diversity of scenarios for faecal contamination and hydrologic events, such as from waterfowl, agricultural animals, resuspended sediments and from the bathers themselves. Examples are provided that suggest that more site-specific targets derived by QMRA could provide insight, directly translatable to management actions.

Meeting report: knowledge and gaps in developing microbial criteria for inland recreational waters.

The U.S. Environmental Protection Agency (EPA) has committed to issuing in 2012 new or revised criteria designed to protect the health of those who use surface waters for recreation. For this purpose, the U.S. EPA has been conducting epidemiologic studies to establish relationships between microbial measures of water quality and adverse health outcomes among swimmers. New methods for testing water quality that would provide same-day results will likely be elements of the new criteria. Although the epidemiologic studies upon which the criteria will be based were conducted at Great Lakes and marine beaches, the new water quality criteria may be extended to inland waters (IWs). Similarities and important differences between coastal waters (CWs) and IWs that should be considered when developing criteria for IWs were the focus of an expert workshop. Here, we summarize the state of knowledge and research needed to base IWs microbial criteria on sound science. Two key differences between CWs and IWs are the sources of indicator bacteria, which may modify the relationship between indicator microbes and health risk, and the relationship between indicators and pathogens, which also may vary within IWs. Monitoring using rapid molecular methods will require the standardization and simplification of analytical methods, as well as greater clarity about their interpretation. Research needs for the short term and longer term are described.

The potential implications of person-to-person transmission of viral infection for US EPA's Groundwater Rule.

The risk characterization method employed by US EPA to quantitatively characterize the benefits of the Groundwater Rule (GWR) for drinking water computes person-to-person transmission intensity as the product of the number of primary illnesses and a static secondary morbidity factor. A population level infectious disease health effects model is used here to evaluate the implications of secondary transmission on exposures to viruses that are relevant to the GWR. These implications are evaluated via a hypothetical case study in which it is assumed that a tour group from a large population centre visits an outlying area that is served by a non-community water system with untreated or inadequately treated groundwater that is contaminated with a highly infectious virus. It is assumed that some of the exposed individuals become infected and then return home. Numerical simulations are used to estimate the subsequent number of additional infections and illnesses due to secondary transmission within the large community. The results indicate that secondary transmission could substantially impact the predicted benefits of the GWR depending on the suite of population dynamic elements and assumptions employed.

A sea change ahead for recreational water quality criteria.

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.

Strategies to reduce person-to-person transmission during widespread Escherichia coli O157:H7 outbreak.

During the Escherichia coli O157:H7 outbreak in 2006 in the United States, the primary strategy to prevent illness was to advise consumers not to eat spinach. No widespread warnings were issued about preventing person-to-person (secondary) transmission. A disease transmission model, fitted to the current data, was used to investigate likely reductions in illnesses that could result from interventions to prevent secondary transmission. The model indicates that exposure to contaminated spinach occurred early in the outbreak and that secondary transmission was similar to that in previous E. coli outbreaks ( 12%). The model also suggests that even a modestly effective strategy to interrupt secondary transmission (prevention of only 2%-3% of secondary illnesses) could result in a reduction of 5%-11% of symptomatic cases. This analysis supports the use of widespread public health messages during outbreaks of E. coli O157:H7 with specific advice on how to interrupt secondary transmission.

Use of microbial risk assessment to inform the national estimate of acute gastrointestinal illness attributable to microbes in drinking water.

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.

A public health evaluation of recreational water impairment.

Water quality objectives for body contact recreation (REC-1) in Newport Bay, CA are not being attained. To evaluate the health implications of this non-attainment, a comprehensive health-based investigation was designed and implemented. Bacterial indicator data indicate that exceedances of the water quality objectives are temporally sporadic, geographically limited and most commonly occur during the time of the year and/or in areas of the bay where the REC-1 use is low or non-existent. A disease transmission model produced simulated risk estimates for recreation in the Bay that were below levels considered tolerable by the US EPA (median estimate 0.9 illnesses per 1,000 recreation events). Control measures to reduce pathogen loading to Newport Bay are predicted to reduce risk by an additional 16% to 50%. The results of this study indicate that interpreting the public health implications of fecal indicator data in recreational water may require a more rigorous approach than is currently used.

A dynamic model to assess microbial health risks associated with beneficial uses of biosolids.

There is increasing interest in the development of a microbial risk assessment methodology for regulatory and operational decision making. This document presents a methodology for assessing risks to human health from pathogen exposure using a population-based model that explicitly accounts for properties unique to an infectious disease process, specifically secondary transmission and immunity. To demonstrate the applicability of this risk-based method, numerical simulations were carried out for a case study example in which the route of exposure was direct consumption of biosolids-amended soil and the pathogen present in the soil was enterovirus. The output from the case study yielded a decision tree that differentiates between conditions in which the relative risk from biosolids exposure is high and those conditions in which the relative risk from biosolids is low. This decision tree illustrates the interaction among the important factors in quantifying risk. For the case study example, these factors include biosolids treatment processes, the pathogen shedding rate of infectious individuals, secondary transmission, and immunity. Further refinement in methods for determining biosolids exposures under field conditions would certainly increase the utility of these approaches.