Consensus Report

Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

Recent and forecasted advances in microbiology, molecular biology, and analytical chemistry have made it timely to reassess the current paradigm of relying predominantly or exclusively on traditional bacterial indicators for all types of waterborne pathogens. Nonetheless, indicator approaches will still be required for the foreseeable future because it is not practical or feasible to monitor for the complete spectrum of microorganisms that may occur in water, and many known pathogens are difficult to detect directly and reliably in water samples. This comprehensive report recommends the development and use of a "tool box" approach by the U.S Environmental Protection Agency and others for assessing microbial water quality in which available indicator organisms (and/or pathogens in some cases) and detection method(s) are matched to the requirements of a particular application. The report further recommends the use of a phased, three-level monitoring framework to support the selection of indicators and indicator approaches.

Key Messages

  • In contrast, epidemiologic studies involving recreational bathing waters have shown predictive associations between several swimming-associated health effects and various microbial indicators or pathogens.
  • This gap occurs because most outbreak investigations include primarily the epidemiologic component, which concentrates on linking illness to water and might include determination of the agent in clinical specimens, but tends to neglect the environmental component, which would include the determination of water quality through measurement of indicator and pathogen occurrence in water.
  • Under the SDWA Amendments of 1996, recently completed epidemiologic studies of drinking water and endemic disease have focused on establishing associations between water consumption and gastrointestinal illness. Thus far, they have not established a good correlation between indicators of waterborne pathogens, the pathogens themselves, and adverse human health effects, although some earlier studies have shown an association between tap water and endemic gastrointestinal illness with attributable fractions ranging between 14-40 percent.
  • A major problem with present water contact warning systems is that bacterial indicator concentrations are spatiotemporally variable and most sampling is too infrequent to transcend this granularity.
  • Although evolving detection methods will be increasingly able to rapidly detect specific pathogens, the use of well-characterized (conventional) indicator approaches will continue to be necessary because our understanding of existing and emerging pathogens will never be complete.
  • Another shortcoming of present warning systems is the poorly established relationship between presently used indicators and health risk.
  • At present, most water quality measurement methods are single-parameter based.
  • EPA's guidance has been of mixed value, and in this regard the committee concludes that (1) the selection of enterococci for screening at marine recreational beaches is appropriate, because enterococci have been shown to have the best relationship to health risk; (2) existing and proposed monitoring requirements for surface water sources of drinking water are irregular and are not supported by adequate research; and (3) proposed monitoring requirements for groundwater are not adequately protective for viral pathogens.
  • Epidemiologic methods are a well-established and essential tool for determining linkage between the presence of identified waterborne pathogens and their indicators and human disease.However, the significant cost and methodological difficulty of designing, conducting, and interpreting such studies have limited their use.
  • Existing and candidate indicator organisms should have ecologies and responses to environmental variations similar to those of the pathogenic organisms that they are supposed to be indicating. Furthermore, environmental changes may lead to changes in selective pressures resulting in new strains of pathogens with different traits.
  • Groundwater quality monitoring is rare, despite data showing that the majority of waterborne outbreaks of disease in the United States result from groundwater systems.
  • Historically, EPA has focused much of its investment on indicators and indicator systems that are used at the screening level (A), but there is an increasing need for national leadership and guidance for the phases of microbial investigation that follow screening.
  • Many public health applications use microbiological indicators, including public health warning systems, source identification, and status or trends assessments. No single indicator or analytical method (or even a small set of indicators or analytical methods) is appropriate to all applications. A suite of indicators and indicator approaches is required for different applications and different geographies.
  • Several factors limit the effectiveness of current recreational water warning systems, the most prominent of which is the delay in warnings caused by long laboratory sample processing times.
  • The comprehensiveness of investigations of waterborne disease outbreak in the United States varies by the type of outbreak and by state, and results are compiled in CDC's surveillance system.However, this system has low sensitivity and does not consistently provide information that links indicator and pathogen data with adverse health outcomes.
  • There are many promising microbial source identification techniques that can help in deciding whether a health warning should be issued or in identifying the best approach for fixing the problem. However, these techniques are not yet standardized or fully tested.
  • There is need for a database that compiles and serves as a clearinghouse for all microbiological methods that have been utilized and published for studying water quality.
  • To move new methods into the main-stream, a process is required that not only allows for standardization and validation but also facilitates widespread acceptance and implementation.The committee concludes that the AOAC Peer-Verified approach or its equivalent may be the best way forward.
  • Understanding the ecology and evolution of pathogens will provide insights into their pathways of transmission, modes of distribution, potential to reemerge in the future, or emergence in other environments.