Receiver-Operating Characteristics Analysis of Fecal Indicator Bacteria and Pathogens

A receiver-operating characteristics (ROC) curve is a graphical plot of the “sensitivity” (or true positive, TP, rate) against “1-specificity” (or false positive, FP, rate) of test with regard to some true condition of interest. The area under a ROC curve can be interpreted as the probability that a given test correctly ranks a TP diagnostic condition higher than a true negative (TN) diagnostic condition, providing a metric for evaluating the diagnostic quality of a given test. Using ROC analysis, this paper evaluates the diagnostic value of six indicator tests with regard to two waterborne pathogens. Specifically, we compare the diagnostic value of culture-based assays for enterococci and E. coli, somatic coliphage, F+ coliphage, and quantitative polymerase chain reaction (qPCR)-based assays for enterococci and E. coli with regard to the presence or absence of Giardia and Cryptosporidium. The results of this study indicate that qPCR based assays of enterococci and E. coli are superior to culture-based assays of the same organisms with regard to diagnosing the presence of Giardia.