Receiver-operating characteristics analysis: a new approach to predicting the presence of pathogens in surface waters.

Fecal indicator microbes are used to monitor the public health risks of recreating in surface waters. However, the importance of indicator tests as predictors of waterborne pathogens has been unclear. Numerous studies have also shown that the survival and growth of indicator organisms may depend on location-specific factors that cannot be broadly generalized. We used receiver-operating characteristic (ROC) methods to determine whether fecal indicator species are capable of predicting the presence of Giardia and Cryptosporidium in fresh surface waters in the Chicago area. We also derived recreational water quality criteria specific to our location with respect to this end point. We considered five fecal indicators: enterococci measured by culture and quantitative polymerase chain reaction (qPCR), Escherichia coli measured by culture, somatic coliphage, and F+ coliphage. All fecal indicators were found to predict the presence and absence of protozoan pathogens. The test for enterococci measured by culture was the poorest predictor of the presence of pathogens. The test for enterococci measured by qPCR was the best predictor of the presence of Giardia, but not an important predictor of the presence of Cryptosporidium. The test for somatic coliphage was a relatively strong predictor of the presence of both pathogens. This analysis supports the use of qPCR-based assays over culture-based assays for predicting the presence of Giardia in fresh surface water. Our criteria were optimized for the prediction of the presence of Giardia and Cryptosporidium in our location and were closely aligned with criteria of the U.S. Environmental Protection Agency derived from epidemiological risk assessment. The ROC approach is flexible and can inform location-specific interpretation of water quality monitoring data and decision making.

A comparison of rapid and conventional measures of indicator bacteria as predictors of waterborne protozoan pathogen presence and density.

E. coli and enterococci in recreational waters are monitored as indicators of fecal contamination, pathogen presence, and health risk. Quantitative polymerase chain reaction (qPCR) tests for fecal indicator bacteria can provide beach managers with same-day information about water quality, unlike culture methods which provide that information the following day. The abilities of qPCR measurements of indicator bacteria, as compared to culture measurements of indicator bacteria, as predictors of pathogen presence or density in surface waters are not well understood. The purpose of this study was to make such comparisons between water samples collected from Chicago area surface waters, including rivers, inland lakes, Lake Michigan, and the Chicago Area Waterways System, which is dominated by wastewater effluent. A total of 294 twenty-litre samples were collected and analyzed for Giardia and Cryptosporidium. qPCR and membrane filtration methods were used to quantify E. coli and enterococci. Correlation, logistic regression, and zero-inflated Poisson modeling were utilized to evaluate associations between indicators and parasites. qPCR and culture measures of the indicator bacteria were similar in their ability to predict parasite presence and density. Correlations between parasites and indicators were generally stronger at waters not dominated by effluent. Associations between indicator density and Giarida presence were observed more consistently than between indicator density and Cryptosporidium presence. Associations between enterococci and parasites were generally stronger than associations between E. coli and parasites. The use of qPCR monitoring in our setting would generate more timely results without compromising the ability to predict parasite presence or density.