Project: California Epidemiological Studies

Background and Objectives

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

To address this, SCCWRP plans to conduct three epidemiology studies between 2007 and 2009. The first will be at Doheny State beach in Dana Point, which is a site where the bacterial inputs are thought to be primarily from nonhuman sources (birds, urban runoff). The second is Avalon Beach on Catalina Island, where a leaking sewage infrastructure is believed to be the predominant bacterial source. The third is Surfrider Beach in Malibu, where local septic systems, birds and urban runoff are all believed to contribute to the bacterial load. 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.

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?

Status

This is an ongoing study with anticipated completion in 2011.

Methods

The study is being conducted using a prospective cohort design, in which swimmers (and nonswimmers) are monitored for water exposure while at the beach and surveyed for illness that occurs in the two weeks subsequent to their beach visit. They will be queried with respect to gastrointestinal, respiratory, dermatological, ear, eye, and other nonspecific symptoms. An anticipated 25,000 beachgoers will be queried across these three studies.

Water quality will be assessed at the same times and locations as beachgoer recruitment in order to assess swimmer exposure. Measurements will include both traditional and non-traditional indicators. Traditional FIB methods quantify total coliform, fecal coliform, and enterococcus using membrane filtration. Enterococcus will also be measured using the Enterolert chromogenic substrate method. Nontraditional measurements will include rapid methods for quantifying enterococcus and E. coli, Bacteroides, Bacteroides thetaiotamicron, adenovirus, norovirus, and coliphage (somatic and F+), among others. SCCWRP is taking a collaborative approach, supplying samples to numerous investigators who have developed a variety of methods for new indicators, since the marginal cost for additional sample collection is small relative to the fixed cost of the epidemiological data collection and analysis.

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

Partners

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

For more information on the California epidemiological studies, contact John Griffith at johng@sccwrp.org (714) 755-3228.

This page was last updated on: 03/31/2009