171Introduction and Historical BackgroundINTRODUCTIONThe first outbreak of a waterborne disease to be scientifically documented inmodern Western society occurred in London, England, in 1854. This early epide-miology study by John Snow, a prominent local physician, determined that theconsumption of water from a sewage-contaminated public well led to cholera(Snow, 1854a,b). This connection, decades before the germ theory of diseasewould be hypothesized and proven, was the first step to understanding that watercontaminated with human sewage could harbor microorganisms that threatenpublic health. Since then, epidemiology has been the major scientific disciplineused to study the transmission of infectious diseases through water (NRC, 1999a).In the late nineteenth century and throughout the twentieth century, sanitarypractices were established in the UnhÚed States regarding the handling and dis-posal of sewage, while filtration and chlorination systems were increasingly usedto disinfect drinking water. Through these historical efforts and owing to ongoingadvances in water and wastewater treatment and source water protection, theUnited States has secured and maintains one of the cleanest and safest supplies ofdrinking water in the world. Starting in 1920, national statistics on waterbornedisease outbreaks caused by microorganisms, chemicals, or of unknown etiologyhave been collected by a variety of researchers and federal agencies (Lee et al.,2002). These data demonstrate that several outbreaks still occur every year in thiscountry. Moreover, epidemiologists generally agree that these reported outbreaksrepresent only a fraction of the total that actually occur because many go undetec-ted or unreported (NRC, 1999a). Thus, continued vigilance to protect the publicfrom waterborne disease remains a necessity.18 INDICATORS FOR WATERBORNE PATHOGENSFor more than 100 years, U.S. public health personnel have relied exten-sively on an indicator organism approach to assess the microbiological quality ofdrinking water. These bacterial indicator microorganisms (particularly“coliforms,” described later) are typically used to detect the possible presence ofmicrobial contamination of drinking water by human waste. More specifically,fecal indicator bacteria provide an estimation of the amount of feces, and indi-rectly, the presence and quantity of fecal pathogens in the water. Over the longhistory of their development and use, coliform test methods have been standard-ized, they are relatively easy and inexpensive to use, and enumeration of coliformshas proven to be a useful method for assessing sewage contamination of drinkingwater. In conjunction with chlorination to reduce coliform levels, this practicehas led to a dramatic decrease in waterborne diseases such as cholera and typhoidfever. Furthermore, the use of bacterial indicators has been extended to U.S. “am-bient” waters in recent decades—especially freshwater and marine-estuarine wa-ters used for recreation. However, an increased understanding of the diversity ofwaterborne pathogens, their sources, physiology, and ecology has resulted in agrowing understanding that the current indicator approach may not be as univer-sally protective as was once thought. In this regard, several limitations of bacte-rial indicators for waterborne pathogens have been reported and are discussedthroughout this report.To protect public health, it is important to have accurate, reliable, and scien-tifically defensible methods for determining when water is contaminated by patho-gens and to what extent. Furthermore, recent and forecasted advances in microbi-ology, biology, and analytical chemistry make it timely to assess the currentparadigm of relying predominantly or exclusively on traditional bacterial indica-tors for waterborne pathogens in order to make judgments concerning the micro-biological quality of water to be used for recreation or as a source for drinkingwater supply.Committee and ReportThis report was prepared by the National Research Council (NRC) Commit-tee on Indicators for Waterborne Pathogens—jointly overseen by the NRC’sBoard on Life Sciences and Water Science and Technology Board. The commit-tee consists of 12 volunteer experts in microbiology, waterborne pathogens (bac-teriology, virology, parasitology), aquatic microbial ecology, microbial risk as-sessment, water quality standards and regulations, environmental engineering,biochemistry and molecular biology, detection methods, and epidemiology andpublic health. The report’s conclusions and recommendations are based on a re-view of relevant technical literature, information gathered at four committee meet-ings, a public workshop on indicators for waterborne pathogens (held on Septem-ber 4, 2002), and the collective expertise of committee members.The committee was formed in early 2002 at the request of the U.S. Environ-INTRODUCTION AND HISTORICAL BACKGROUND 19mental Protection Agency (EPA) Office of Water to report on candidate indica-tors and/or indicator approaches (including detection technologies) for microbialpathogen contamination in U.S. recreational waters (excluding coastal marinewater and marine-estuarine water) and source water (including groundwater) fordrinking water.1 It is important to note that the committee’s charge, as outlined inits statement of task (see Box ES-1), was slightly but substantively altered afterits first meeting and subsequent discussions with EPA, most notably to includecoastal and marine-estuarine recreational waters that were originally excluded.As a result, it was agreed that the committee’s report would give less space andemphasis to the importance and public health impacts of waterborne pathogens;place less emphasis on defining currently known waterborne pathogen classesand anticipating those emerging waterborne pathogens that are likely to be ofpublic health concern (although Appendix A provides a brief summary discus-sion and table of new and [re]emerging waterborne pathogens); exclude consider-ation of blue-green algae and their toxins; and not specifically consider how theuse of candidate indicators might allow for determination of an appropriate levelof water treatment needed to protect public health. It is also important to state thatalthough an assessment of suitable indicators for shellfish waters is beyond thescope of this report, some discussion of shellfish experience is included becauseof the (especially historical)