Recreational health risks and public perception of beach water quality: A combined simulation and survey-based approach

Recreational health risks and public perception of beach water quality were assessed in Orange County, California, where illness rates attributable to bathing in intermittently contaminated seawater were not completely known.; A Monte Carlo simulation was performed to evaluate highly credible gastrointestinal (HCGI) risk in marine bathers under exposure-related uncertainties: spatial and temporal patterns of bathing, and the relationship between enterococcus density in seawater and HCGI risk. Federal guidelines were met when risk was averaged over the 31-month study period; however, acceptable risk thresholds were crossed for up to six consecutive days when beaches were open. Approximately 99% of the 95,010 total HCGI cases occurred when beaches were open. Attack rates increased from .88% to 2.16% when 10% of bathers were assumed to have bathed during beach closures. Spatial patterns of exposure accounted for approximately 5.6% of total illness cases. The HCGI attack rate was higher in winter months than summer months due to elevated enterococcus levels coincident with open beaches; however, total illness cases were eight times higher during summer months because of the number of exposures.; Perceived swimming-related health risk was assessed through a survey of beachgoers at two beaches following a major beach closure due to bacterial contamination. Huntington Beach (HB) had been affected by a series of well-publicized closures, while Laguna Beach had been open. Approximately 84% of total respondents had seen at least one media report about the closures in HB, and no significant differences were found in awareness of the closure events. Regression analysis indicated that proximity of residence to the beach was strongly associated with closure awareness. More than 50% of respondents felt that the water was safe for swimming, despite the fact that the HCGI risk was substantially higher at HB and approached acceptable risk thresholds at both beaches in previous weeks. Most beachgoers planned to swim, trusted beach closure decisions made by health officials, and were not highly concerned with health risks of swimming. The discrepancy between measured and perceived risk levels suggested a need for improved risk communication.