Microbial source tracking to address of bacterial contamination in recreational waters

Abstract Background Beach closures in the USA are determined by fecal indicator bacteria thresholds, which are insufficient to identify causes of contamination. We use microbial source tracking (MST) to identify the species source of bacteria entering chronically impaired waters. We find canine bacteria is the primary source of high E.coli levels and demonstrate the power of MST for direction of remediation efforts. Methods This environmental sampling study was performed in Short Beach, Branford, Connecticut, USA. Water samples were collected from outfalls under wet and dry precipitation conditions by 10 Citizen Scientist volunteers. The highest E.coli samples were analyzed for avian, human, and canine markers using MST. Results E.coli from 103 samples was tested from April-October 2023. Pearson’s r between average site E.coli and same day precipitation was 0.71 (p-value = 0.006). Among the high E.coli samples, 19 (76%) were low/non detectable, 5 (20%) were moderate, and 1 (4%) were high for human tracers; 10 (50%) were low/non detectable and 10 (50%) were moderate for avian tracers, and 3 (15%) were low/non detectable, 11 (55%) were moderate, and 6 (30%) were high for canine tracers. Conclusions Precipitation is a driver of elevated bacteria levels. Canine bacteria is likely the primary source of elevated bacterial levels in beach waters, while avian contributors are of moderate concern and human contributors are of low concern. As a result, an education campaign and watertight waste receptacles, rather than costly sewer line replacements, are being deployed to improve beach quality. Key messages • Use of microbial source tracking found canine bacteria is the likely driver of elevated E.coli levels in local beaches, initiating a community education campaign rather than costly sewer replacements. • Microbial source tracking technology offers a powerful public health tool for identifying causes of bacterial contamination in chronically impaired recreational waters.