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Project: Wet and Dry Weather Beach Epidemiology Studies

Background and Objectives

A number of epidemiology studies have demonstrated a relationship between fecal indicator bacteria (FIB) and health risk, but they have been mostly conducted on beaches impacted by point sources with known human fecal contributions. Fewer studies have examined this relationship at beaches where non-point sources are the dominant fecal input source.

To address this, SCCWRP followed its 2003 San Diego-area Mission Bay beach epidemiology study with several additional epidemiology studies at beaches with varying characteristics between 2007 and 2014. The first took place at Doheny State beach in Dana Point, where the bacterial inputs are thought to be primarily from nonhuman sources (birds, urban runoff). The second was located at Avalon Beach on Catalina Island, where a leaking sewage infrastructure is believed to be the predominant bacterial source. The third site studied was Surfrider Beach in Malibu, where local septic systems, birds, and urban runoff are all believed to contribute to the bacterial load. Fourth, SCCWRP took on an epidemiology study in the San Diego region targeting surfers who are exposed to the water during wet weather. Together, these sites allow investigation of indicator/health-risk relationships across a spectrum of bacterial input sources with a varying degree of human fecal contribution and weather conditions.

The study focuses on three primary questions:

1) Did water contact increase the risk of illness during the two weeks following exposure to water?
2) Among those individuals with water contact, were there associations between illness and measured levels of traditional water quality indicators?
3) Among those individuals with water contact, were there associations between illness and measured levels of non-traditional water quality indicators?


This study was initiated in 2007 with anticipated completion in 2015.


Epidemiology surveys utilized a prospective cohort design, in which swimmers and non-swimmers were asked about water exposure while at the beach and surveyed to detect illness in the two weeks subsequent to their beach visit. Over 25,000 beachgoers were queried across the three studies at Doheny, Avalon, and Surfrider Beaches with respect to gastrointestinal, respiratory, dermatological, ear, eye, and other nonspecific symptoms.

Water quality was also assessed at the same times and locations as beachgoer recruitment in order to assess the degree of swimmer exposure to pathogens. Measurements included both traditional and non-traditional indicators. Traditional FIB methods quantified total coliform, fecal coliform, and enterococcus using membrane filtration. Enterococcus was also measured using the Enterolert chromogenic substrate method. Nontraditional measurements included rapid methods for quantifying enterococcus and E. coli, Bacteroides, Bacteroides thetaiotamicron, adenovirus, norovirus, and coliphage (somatic and F+), among others. SCCWRP also supplied water samples to numerous partnering investigators who have developed a variety of novel analysis methods.

Water samples were collected at the same time that swimmers were exposed (left); SCCWRP partners interviewed swimmers and followed up with them several days later to determine whether any adverse health effects occurred following exposure (right)

Preliminary Findings

The Surfrider Beach study in Malibu suggested that the three days following a beach visit may be the most relevant period for health outcome measurement in recreational water studies. Although water quality conditions observed in this study were generally good, fecal indicator bacteria levels were not associated with swimmer illness.

Correlations between FIB and human markers were much more frequent at Doheny Beach than at Avalon Beach. Human sewage markers and adenoviruses were routinely detected in samples meeting FIB regulatory standards. Thus, the toolbox approach of FIB measurement coupled with analysis of several MST markers targeting human pathogens demonstrated that human sewage was at least partly responsible for the degradation of water quality, particularly at Doheny Beach.


This project is being conducted in partnership with UC Berkeley, the Orange County Sanitation District, Heal the Bay, and Surfrider International.


Preliminary findings: Doheny State Beach epidemiology study (Video)- January 2011 presentation to SCCWRP member agencies sharing preliminary results from the epidemiology study at Doheny.

For more information on California Epidemiological Studies, contact Ken Schiff at (714) 755-3202 or John Griffith at (714) 755-3228.
This page was last updated on: 7/1/2014