Straight to the Source

New research supports the development of tools that managers can use to prioritize source control and treatment programs.

Project Profile:

Quantification of Pathogens and Sources of Microbial Indicators for QMRA in Recreational Waters (PATH2R08)

Principal Investigator:

Stefan Wuertz, Ph.D., University of California, Davis

For decades, fecal indicator bacteria such as E. coli have been used to establish and enforce recreational water quality criteria. But as our understanding of pathogens and their relationships to indicator bacteria has improved, the shortcomings of using fecal indictor bacteria are becoming more apparent. First, these bacteria provide no information about the sources of microbial pathogen pollution. Second, research has shown that they can persist and multiply in nutrient-rich environmental niches and are present in sediments and on sands at beaches on all U.S. coastlines. As such, exceedances of criteria often occur duet o unknown sources or even absent of a pollution event. Due to these and other issues, U.S. EPA has developed a Critical Science Plan and Criteria Development Plan to update existing recreational water quality criteria.

WERF has developed a complimentary plan to address information gaps that are of importance to operators and owners of municipal wastewater and stormwater management systems, and that will inform U.S. EPA’s criteria revisions. The first research effort under WERF’s pathogens and human health program is the project Informing the Risk-Based Framework for Recreational Waters: Quantification of Microbial Pathogens and Indicators from Various Sources (PATH2R08). Led by Stefan Wuertz, Ph.D., of the University of California, Davis, the project will address some of these gaps and provide U.S. EPA with timely information that can help update ambient water quality criteria for recreational waters. This project is driven by the critical need to improve risk assessment models and water quality criteria as resource managers strive to understand and prioritize management of waterborne pathogen pollution worldwide.

Forming the framework

Research, which began in April 2009, is already underway to compile and analyze existing data regarding the occurrence of pathogens and indicator organisms from a wide range of sources. The focus of the research is on discharges to waterbodies (CSOs, septic systems, etc.). The effort will also entail the collection of new data, through field sampling and lab analysis, regarding the concentrations and overall loads of waterborne pathogens and indicator organisms. Once complete, Wuertz and his team will then analyze and synthesize the data into robust quantitative microbial risk assessment (QMRA) models and risk management frameworks. These will form the basis of tools that watershed managers can use to assess and predict recreational health risks in their own watersheds, and thereby identify actions that could best protect recreational users. Such a framework is critical for managers who face the challenge of complying with recreational water quality criteria.


Epidemiological studies are the most accurate method of calculating risk from exposure to pathogens, but the cost and time involved are limiting. Indeed, very few epidemiological studies are available to quantify human health risks in recreational waters and the available studies may not be representative of many watersheds or conditions. For instance, no epidemiological studies have focused on wet weather conditions. One way in which we can gain a better understanding of the presence of pathogens and their potential to affect human health is by using quantitative microbial risk assessment (QMRA). This multi-stage assessment takes information concerning a specific pathogen, its presence, potential health effects, and movement throughout the watershed, and creates a mathematical model that allows decision makers to calculate a full range of possible risks, including average and worst-case scenarios.

QMRAs can be an important component of criteria development, as well as a valuable resource for treatment plant managers looking to prioritize their efforts to curtail waterborne pathogen pollution. But more data are needed on the relationships between indicators, source identifiers (for example, Bacteroidales), and pathogens to support the use of QMRAs in the frameworks needed for wastewater treatment plants.

In particular, there is significantly less information on the amounts of feces-borne pathogens that are discharged into receiving waters than on pathogens in the receiving waters themselves. Filling in some of these data gaps is a priority for WERF in this project. To help fill the gap, the project team issued a request for information to WERF subscribers to find out what pathogen and source identifier data utilities and other sites are collecting. The research teams sampling and data collection will include animal and septic samples, as well as samples from combined sewer overflows (CSOs), stormwater discharges, and other sources. In addition, it is important that sampling be representative of conditions when recreation occurs, so the research team will also investigate dry weather discharges, which include septic systems; runoff from residential, commercial, and agricultural areas; industrial wastewater; and treated municipal wastewater.


Quantifying pathogens is a difficult task: monitoring methodologies are unable to measure all pathogens of concern, and those pathogens that are targeted can be difficult to detect. Also, a lack of pathogen detection is not necessarily evidence of absence, and pathogens that are detected might not be infective. Recognizing this, the team decided to supplement collected pathogen data with alternative indicators including fecal host associated Bacteroidales.

Bacteroidales is a group of bacteria that are epidemiologically relevant and much more abundant than pathogens in most waters containing recent fecal  ontamination. As strictly anaerobic organisms, they die off more rapidly in ambient waters than E. coli or Enterococcus. And unlike traditional indicators, because they are host-associated, a given Bacteroidales genetic marker can be used in the differentiation between human and nonhuman pollution and in the identification of specific animal sources – important information for source control and treatment programs. Overall, the monitoring toolkit the research team will use to guide QMRA employs a combination of genetic, culture, and microscopy-based methodologies, and is one of the most comprehensive available.

New tools

This research is fundamental to the development of new recreational water quality criteria and management of discharges to recreational waters. It will provide new tools for stakeholders and management agencies involved with developing water quality monitoring criteria, and allow stakeholders to accurately predict health risks and mitigate sources of fecal pollution. It is WERF’s hope that this research effort will advance our current understanding and establish a new state of the science for recreational water quality and risk assessment tools.

To follow the progress of the ongoing research, please visit WERF’s online Pathogens and Human Health knowledge area at