Evaluation of recreational health risk in coastal waters based on enterococcus densities and bathing patterns.

Abstract

We constructed a simulation model to compute the incidences of highly credible gastrointestinal illness (HCGI) in recreational bathers at two intermittently contaminated beaches of Orange County, California. Assumptions regarding spatial and temporal bathing patterns were used to determine exposure levels over a 31-month study period. Illness rates were calculated by applying previously reported relationships between enterococcus density and HCGI risk to the exposure data. Peak enterococcus concentrations occurred in late winter and early spring, but model results showed that most HCGI cases occurred during summer, attributable to elevated number of exposures. Approximately 99% of the 95,010 illness cases occurred when beaches were open. Model runs were insensitive to 0-10% swimming activity assumed during beach closure days. Comparable illness rates resulted under clustered and uniform bather distribution scenarios. HCGI attack rates were within federal guidelines of tolerable risk when averaged over the study period. However, tolerable risk thresholds were exceeded for 27 total days and periods of at least 6 consecutive days. Illness estimates were sensitive to the functional form and magnitude of the enterococcus density-HCGI relationships. The results of this study contribute to an understanding of recreational health risk in coastal waters.

Public Mis-Notification of Coastal Water Quality: A Probabilistic Evaluation of Posting Errors at Huntington Beach, California

“…horizontal line), peaking at about 60 excess illnesses per 1000 bathers; these illness attack rates are in the range estimated by other researchers for the Huntington Beach area (26). Now-casts for the exceedence probability (fourth panel) exhibit spring-neap cycling, and importantly, periods of high exceedence probability (e.g., Pex|l > 0.2) generally coincide with single-sample violations (compare second and fourth panels, Figure 5).…”

Regional Public Health Cost Estimates of Contaminated Coastal Waters: A Case Study of Gastroenteritis at Southern California Beaches

“…Our estimates for the same stretch of shoreline are higher (68,011 and 87, 513 excess GI based on models C and K, respectively). Not only did we use a different measure of illness (GI vs. HCGI) we also used a Monte Carlo scheme to estimate ENT on unsampled days whereas Turbow et al (18) used linear interpolation, and we used higher, empirically determined (18) estimate to determine that the health costs of excess GI at the same beaches were $1.2 million. Our health cost estimates are higher ($2.3 and $2.9 million for models C and K, respectively), due to the higher incidence of ilness predicted by our models.…”

“…ENT densities on unsampled days during 2000 were estimated by randomly sampling from the appropriate seasonal distribution. Because day-to-day ENT concentrations at marine beaches are weakly correlated and variable (17), we chose not to follow the estimation method of Turbow et al (18) who assumed a linear relationship between day-to-day ENT densities at two CA beaches. Comparisons between the Monte Carlo method and a method that simply used the monthly arithmetic average ENT density indicated the two provided similar results (data not shown).…”

“…Of all the illnesses considered in the literature, GI is most commonly associated with exposure to polluted water (10)(11)(12)(21)(22)(23)(24)(25)(26). To estimate the risk of GI from swimming in contaminated marine waters in southern CA, we utilized two dose-response models (11,12) (Table 1) developed in epidemiology studies conducted elsewhere (in marine waters of the East U.S. coast and United Kingdom) (18,27). A local dose-response model for GI would be preferable, but does not exist.…”

Recreational use assessment of water-based activities, using time-lapse construction cameras

“…Multiple studies have reported usage frequency for swimmers and non-swimmers based on records of lifeguards stands, 3,4 or conducted randomized trials for evaluating exposure differences between bathers and non-bathers. 5 At least one study used aerial photographs in conjunction with interviews of state officials.…”