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Using rapid indicators for Enterococcus to assess the risk of illness after exposure to urban runoff contaminated marine water
- Colford, John M., Jr., Schiff, Kenneth C., Griffith, John F., Yau, Vince, Arnold, Benjamin F., Wright, Catherine C., Gruber, Joshua S., Wade, Timothy J., Burns, Susan, Hayes, Jacqueline, McGee, Charles, Gold, Mark, Cao, Yiping, Noble, Rachel T., Haugland, Richard, Weisberg, Stephen B.
- Water research 2012 v.46 no.7 pp. 2176-2186
- Enterococcus, coliform bacteria, deglutition, diarrhea, gastrointestinal system, indicator species, quantitative polymerase chain reaction, rapid methods, risk, sand, streams, urban runoff
- BACKGROUND: Traditional fecal indicator bacteria (FIB) measurement is too slow (>18 h) for timely swimmer warnings. OBJECTIVES: Assess relationship of rapid indicator methods (qPCR) to illness at a marine beach impacted by urban runoff. METHODS: We 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. RESULTS: We 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. CONCLUSIONS: We 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.