Volunteer monitoring of E. coli in streams of the upper Midwestern United States: a comparison of methods

Fecal contamination of water is a public health concern for those using the water for drinking or recreation. The EPA recommends using Escherichia coli to evaluate recreational freshwaters for fecal contamination. 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 two E. coli monitoring methods used by volunteers: Coliscan Easygel® and 3M^TM Petrifilm^TM, incubated for 24 and 48 hours. The methods were assessed to determine how closely each matched results with EPA-approved laboratory analyses. Analysis of covariance results indicated that when used by volunteers to monitor surface water, 3M^TM Petrifilm^TM results were more similar to laboratory analyses than Coliscan Easygel®. Both test methods had similar overall accuracy of predicting if a sample exceeded or fell below the 235 cfu/100 mL EPA body contact standard for recreational surface waters. Two-thirds of volunteers preferred 3M^TM Petrifilm^TM.