Water quality indicators and the risk of illness at beaches with nonpoint sources of fecal contamination.
BACKGROUND
Indicator bacteria are a good predictor of illness at marine beaches that have point sources of pollution with human fecal content. Few studies have addressed the utility of indicator bacteria where nonpoint sources are the dominant fecal input. Extrapolating current water-quality thresholds to such locations is uncertain.


METHODS
In a cohort of 8797 beachgoers at Mission Bay, California, we measured baseline health at the time of exposure and 2 weeks later. Water samples were analyzed for bacterial indicators (enterococcus, fecal coliforms, total coliforms) using both traditional and nontraditional methods, ie, chromogenic substrate or quantitative polymerase chain reaction. A novel bacterial indicator (Bacteroides) and viruses (coliphage, adenovirus, norovirus) also were measured. Associations of 14 health outcomes with both water exposure and water quality indicators were assessed.


RESULTS
Diarrhea and skin rash incidence were the only symptoms that were increased in swimmers compared with nonswimmers. The incidence of illness was not associated with any of the indicators that traditionally are used to monitor beaches. Among nontraditional water quality indicators, associations with illness were observed only for male-specific coliphage, although a low number of participants were exposed to water at times when coliphage was detected.


CONCLUSIONS
Traditional fecal indicators currently used to monitor these beaches were not associated with health risks. These results suggest a need for alternative indicators of water quality where nonpoint sources are dominant fecal contributors.
Colford
John M
JM
University of California Berkeley, School of Public Health, Division of Epidemiology, Berkeley, CA 94720-7360, USA. jcolford@berkeley.edu
Wade
Timothy J
TJ
Schiff
Kenneth C
KC
Wright
Catherine C
CC
Griffith
John F
JF
Sandhu
Sukhminder K
SK
Burns
Susan
S
Sobsey
Mark
M
Lovelace
Greg
G
Weisberg
Stephen B
SB
D000293:Adolescent; D000328:Adult; D001439:Bacteroides / Q000235:genetics / Q000302:isolation & purification; D001493:Bathing Beaches; D002140:California; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004403:Dysentery; D004755:Enterobacteriaceae / Q000235:genetics / Q000302:isolation & purification*; D004781:Environmental Exposure / Q000517:prevention & control / Q000706:statistics & numerical data*; D004784:Environmental Monitoring / Q000379:methods*; D062665:Epidemiological Monitoring; D005243:Feces / Q000382:microbiology; D005260:Female; D005767:Gastrointestinal Diseases / Q000453:epidemiology; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D010038:Otorhinolaryngologic Diseases / Q000453:epidemiology; D012307:Risk Factors; D012623:Seawater / Q000009:adverse effects / Q000382:microbiology / Q000821:virology; D012874:Skin Diseases, Infectious / Q000453:epidemiology; D013550:Swimming; D014876:Water Pollution / Q000032:analysis*