Coliphage densities in Chicago area waterways: Implications for water quality monitoring

Background: The Chicago Area Waterways System (CAWS) consists of 78 miles of rivers and canals that divert urban drainage and wastewater away from Lake Michigan, the primary water source for the Chicago metropolitan area. These waterways receive treated but non-disinfected wastewater from multiple treatment facilities, potentially putting recreational users of these waters at higher risk of gastrointestinal illness. A number of studies have suggested that coliphage densities might be better measures of microbial water quality than traditional indicators, such as total coliforms, fecal coliforms and enterococcus. Methods: Water samples were collected as part of the Chicago Health, Environmental Exposure, and Recreation Study (CHEERS). This is a cohort study that evaluates the incidence of illness in recreational users of the Chicago Area Waterways System. This incidence rate is compared to that observed among recreational users of general use inland lakes, flowing waters, and Lake Michigan, as well as people engaging in outdoor recreation that does not involve water contact. These water samples were analyzed according to EPA method 1602 to determine densities of somatic and male-specific coliphages. Results: Over 2000 samples were collected and analyzed for somatic and male-specific coliphage levels. We summarize quality monitoring data of coliphage densities, and compare coliphage densities in samples from Lake Michigan, the Chicago River System, inland lakes, and flowing inland waters. Discussion: Coliphage densities show potential as measures of microbial water quality. We discuss the public health advantages and disadvantages of measuring coliphages rather than traditional indicators.