Using rapid indicators for Enterococcus to assess the risk of illness after exposure to urban runoff contaminated marine water

BackgroundTraditional fecal indicator bacteria (FIB) measurement is too slow (>18 h) for timely swimmer warnings.ObjectivesAssess relationship of rapid indicator methods (qPCR) to illness at a marine beach impacted by urban runoff.MethodsWe measured baseline and two-week health in 9525 individuals visiting Doheny Beach 2007–08. Illness rates were compared (swimmers vs. non-swimmers). FIB measured by traditional (Enterococcus spp. by EPA Method 1600 or Enterolert™, fecal coliforms, total coliforms) and three rapid qPCR assays for Enterococcus spp. (Taqman, Scorpion-1, Scorpion-2) were compared to health. Primary bacterial source was a creek flowing untreated into ocean; the creek did not reach the ocean when a sand berm formed. This provided a natural experiment for examining FIB-health relationships under varying conditions.ResultsWe observed significant increases in diarrhea (OR 1.90, 95% CI 1.29–2.80 for swallowing water) and other outcomes in swimmers compared to non-swimmers. Exposure (body immersion, head immersion, swallowed water) was associated with increasing risk of gastrointestinal illness (GI). Daily GI incidence patterns were different: swimmers (2-day peak) and non-swimmers (no peak). With berm-open, we observed associations between GI and traditional and rapid methods for Enterococcus; fewer associations occurred when berm status was not considered.ConclusionsWe found increased risk of GI at this urban runoff beach. When FIB source flowed freely (berm-open), several traditional and rapid indicators were related to illness. When FIB source was weak (berm-closed) fewer illness associations were seen. These different relationships under different conditions at a single beach demonstrate the difficulties using these indicators to predict health risk.

Figure optionsDownload high-quality image (373 K)Download as PowerPoint slideHighlights
► Cohort design evaluated swimmer health-fecal indicator bacteria (FIB) relationships.
► Rapid (qPCR) and traditional (culture-based) methods used to enumerate FIB.
► Swimming, and increased water exposure, associated with negative health outcomes.
► Health-FIB relationship depended on beach conditions and swimmer’s water exposure.
► Demonstrated difficulties using FIB to predict health outcomes at marine beach.