Fecal Bacteria off Southern California Beaches

Semenza (2012) et al. found that the concentrations of fecal bacteria in the waters off the coast of  coast of three major counties  (Los Angeles, Santa Monica, and San Diego) in Southern California have a direct correlation to the intensity of rain events in the surrounding areas. Higher concentrations of bacteria are observed after higher intensity rainfalls have occurred. In light of this correlation, it was predicted that disease burdens, such as gastrointestinal illness, skin, ear, eye, and nose infections, due to the high levels of fecal bacteria concentration in the water (as a result of large amounts of discharged unfiltered urban stromwater runoff) may decrease because of ongoing climates changes that project hotter and drier weather conditions. Less rain would imply less runoff, which should result in lower concentrations of bacteria and lower risk of disease. Despite the projected decline in rainfall, by 416%, it is still unclear how certain the disease burden is predicted to decrease since chances of high variability are recorded for future weather patterns.—Genevieve Heger

                  Semenza, J. C., Caplan, J. S., Buescher, G., Das, T., Brinks, M. V., Gershunov, A. 2012. Climate Change and Microbiological Water Quality at California Beaches. EcoHealth 9, 293–297
                  Semenza et. al derived a linear model of microbiological water contamination (mean Enterococcusconcentrations) for 78 southern California beaches using Enterococcus and precipitation data. Data collected between 20002004 were used for estimations, and data from 2005 were used as validation. Enterococcusdata from Brinks et al. 2008 were also used. Predictions for future Enterococcuswater contamination levels were determined after projected precipitation levels were derived from the CNRM CM3 global climate model under the SRESA2 ‘business-as-usual’ scenario (IPCC 2007), which was downscaled for Huntington Beach using bias-corrected constructed analogues (BCCA). The annual means for projected Enterococcus levels were computed and the data were grouped by decade for the twenty-first century. Disease burden, as a result of projected contamination levels, were modeled according to two published dose–response relationships.
                  Precipitation was significantly related to measured Enterococcusconcentration between 2000-2004. A projected decrease in precipitation levels by 416% suggest that a relative decrease in coastal water contamination may occur, which provides a positive implication for infectious disease burden among recreational water users. However, due to the large variance in the empirical water quality and projected precipitation data, and differences in the dose response curves, we concluded that it is currently difficult to accurately predict disease burden.
Reference:
Brinks MV, Dwight RH, Osgood ND, Sharavanakumar G, Turbow DJ, El-Gohary M, et al. (2008) Health risk of bathing in southern California coastal waters. Archives of Environmental & Occupational Health 63(3):123–135

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