Volunteer Monitoring of E. coli in Streams: A Comparison of Methods

Bacterial contamination of surface waters is a common public health concern. With limited resources available, states have recently focused on training volunteers to expand data collection and resource assessment. Several bacteria testing methods are available for use by the public; however, few studies have comprehensively evaluated their use by volunteers. This study evaluated the reliability and usability of six test methods for monitoring E. coli bacteria when used by volunteers. Initial results found that IDEXX Colisure®, IDEXX Colilert®, incubated Coliscan Easygel® and 3M™ Petrifilm™ matched well with USEPA-approved laboratory analyses. Due to high startup costs associated with the IDEXX methods, only the latter two methods were selected for further assessment. Analysis of covariance results indicated that when used by volunteers to monitor surface water, 3M™ Petrifilm™ results were more similar to laboratory analyses than Coliscan Easygel®. This method had a more equal and reasonably low rate of false positives and missed risk than Coliscan Easygel®. However, both test methods had similar overall accuracy of predicting if a sample was above or below the 235 cfu/100 ml EPA body contact standard for recreational surface waters. Two-thirds of volunteers preferred 3M™ Petrifilm™. Although both methods can be used as a screening tool for E. coli in surface waters, local community groups should consider their desired uses of the data, along with available funding prior to selecting their preferred method.