Effect of submarine groundwater discharge on bacterial indicators and swimmer health at Avalon Beach, CA, USA.
Use of fecal indicator bacteria (FIB) for monitoring beach water quality is based on their co-occurrence with human pathogens, a relationship that can be dramatically altered by fate and transport processes after leaving the human intestine. We conducted a prospective cohort study at Avalon Beach, California (USA), where the indicator relationship is potentially affected by the discharge of sewage-contaminated groundwater and by solar radiation levels at this shallow, relatively quiescent beach. The goals of this study were to determine: 1) if swimmers exposed to marine water were at higher risk of illness than non-swimmers; 2) if FIB measured in marine water were associated with swimmer illness, and; 3) if the associations between FIB and swimmer health were modified by either submarine groundwater discharge or solar radiation levels. There were 7317 individuals recruited during the summers of 2007-08, 6165 (84%) of whom completed follow-up within two weeks of the beach visit. A total of 703 water quality samples were collected across multiple sites and time periods during recruitment days and analyzed for FIB using both culture-based and molecular methods. Adjusted odds ratios (AOR) indicated that swimmers who swallowed water were more likely to experience Gastrointestinal Illness (GI Illness) within three days of their beach visit than non-swimmers, and that this risk was significantly elevated when either submarine groundwater discharge was high (AOR [95% CI]:2.18 [1.22-3.89]) or solar radiation was low (2.45 [1.25-4.79]). The risk of GI Illness was not significantly elevated for swimmers who swallowed water when groundwater discharge was low or solar radiation was high. Associations between GI Illness incidence and FIB levels (Enterococcus EPA Method 1600) among swimmers who swallowed water were not significant when we did not account for groundwater discharge, but were strongly associated when groundwater discharge was high (1.85 [1.06, 3.23]) compared to when it was low (0.77 [0.42, 1.42]; test of interaction: P = 0.03). These results demonstrate the need to account for local environmental conditions when monitoring for, and making decisions about, public health at recreational beaches. The views expressed in this article are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency.
School of Public Health, University of California, Berkeley and Kaiser Permanente Division of Research, United States.
Vincent M
VM
Yau
Southern California Coastal Water Research Project, United States.
Kenneth C
KC
Schiff
School of Public Health, University of California, Berkeley, United States.
Benjamin F
BF
Arnold
Southern California Coastal Water Research Project, United States.
John F
JF
Griffith
School of Public Health, University of California, Berkeley, United States.
Joshua S
JS
Gruber
School of Public Health, University of California, Berkeley, United States.
Catherine C
CC
Wright
United States Environmental Protection Agency, National Environmental Health Effects Research Laboratory, Chapel Hill, United States.
Timothy J
TJ
Wade
University of California, Berkeley, Survey Research Center, United States.
Susan
S
Burns
University of California, Berkeley, Survey Research Center, United States.
Jacqueline M
JM
Hayes
Orange County Sanitation District, United States.
Charles
C
McGee
Institute of Environment and Sustainability, University of California, Los Angeles, United States.
Mark
M
Gold
Southern California Coastal Water Research Project, United States.
Yiping
Y
Cao
Environmental and Water Studies, Dept. Civil & Environmental Engineering, Stanford University, Stanford, CA 94305, United States.
Alexandria B
AB
Boehm
Southern California Coastal Water Research Project, United States.
Stephen B
SB
Weisberg
School of Public Health, University of California, Berkeley, United States. Electronic address: jcolford@berkeley.edu.
John M
JM
Colford
D000293:Adolescent; D000328:Adult; D001493:Bathing Beaches; D002140:California; D002648:Child; D002675:Child, Preschool; D004784:Environmental Monitoring / Q000379:methods; D005243:Feces / Q000382:microbiology; D005260:Female; D005767:Gastrointestinal Diseases / Q000209:etiology; D060587:Groundwater / Q000737:chemistry* / Q000382:microbiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012307:Risk Factors; D012722:Sewage; D013472:Sunlight; D013550:Swimming; D013997:Time Factors; D014865:Waste Disposal, Fluid / Q000379:methods; D014871:Water Microbiology; D014873:Water Pollutants; D055815:Young Adult
D012722:Sewage; D014873:Water Pollutants
Gastrointestinal illness; Indicator organisms; Marine water; Water quality; qPCR