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What is the relative health risk to swimmers from California Seagull feces compared to bather shedders?
Citation:
Schoen, M. AND N. ASHBOLT. What is the relative health risk to swimmers from California Seagull feces compared to bather shedders? Presented at National Beach Conference, Huntington Beach, CA, April 20 - 22, 2009.
Impact/Purpose:
1. What is the predicted gastro-intestinal infection risk to swimmers from Campylobacter jejuni, Cryptosporidium sp., and Rotavirus from human bathers and Campylobacter jejuni from seagulls when the beach water enterococci count is 104 cfu/100mL? 2. Under what fecal loading source apportionment might the predicted risk to swimmers from seagulls equal or exceed the predicted risk from bather shedders?
Description:
Estimated infection risks to swimmers from California seagull and bather sources of fecal contamination at a beach in Southern California were compared using quantitative microbial risk assessment (QMRA). The risk to swimmers of gastro-intestinal infections was estimated from Campylobacter jejuni, Cryptosporidium hominis, and Norovirus from human bathers and Campylobacter jejuni from Californian seagulls over the observed range of surfzone enterococci (ENT) concentration during normal summer conditions at Dohney Beach. A beta-Poisson dose-response model was utilized with pathogen specific parameters to calculate the probability of infection using Monte Carlo analysis of the uncertain input variables. Overall, the individual risks from C. jejuni and Norovirus were greater than that from C. hominis. Specific predictions of risk remain uncertain due to large uncertainty in model parameters; particularly the proportion of Campylobacter strains that are human infectious. If the proportion of infectious strains from gulls is low, near 0.01, then human infection risk from accidental ingestion of bathing water containing gull feces is only greater than the risk from bather shedders when gull fecal matter in the bathing waters exceeds that from humans by more than 20 times; that reduces to four times should the proportion of infectious C. jejuni gull strains be 0.05. The best estimate model results indicated that gull fecal-derived enterococci counts contribute less of a health threat to swimmers than human sources; however there remains large uncertainty in prediction due to the remaining uncertainty in human infectious campylobacter species in gull feces, their unknown environmental persistence and the level of bather shedding of human pathogens.