Fecal source tracking, the indicator paradigm, and managing water quality

Fecal source tracking is used because standard methods of measuring fecal contamination in water by enumerating fecal indicator bacteria (FIB) do not identify the sources of the contamination. This paper presents a critical review of source tracking with emphasis on the extent to which methods have been tested (especially in comparison with other methods and/or with blind samples), when methods are applicable, their shortcomings, and their usefulness in predicting public health risk or pathogen occurrence. In addition, the paper discusses the broader question of whether fecal source tracking and fecal indicator monitoring is the best approach to regulate water quality and protect human health. Many fecal source-tracking methods have only been tested against sewage or fecal samples or isolates in laboratory studies (proof of concept testing) and/or applied in field studies where the “real” answer is not known, so their comparative performance and accuracy cannot be assessed. For source tracking to be quantitative, stability of ratios between host-specific markers in the environment must be established. In addition, research is needed on the correlation between host-specific markers and pathogens, and survival of markers after waste treatments. As a result of the exclusive emphasis on FIB in legislation, monitoring has concentrated on FIB and lost sight of pathogens. A more rational approach to regulating water quality would start with available epidemiological data to identify pathogens of concern in a particular water body, and then use targeted pathogen monitoring coupled with targeted fecal source tracking to control them. Baseline monitoring of indicators would become just one tool among many.