John M. Colford Jr.

Timothy J. Wade

Kenneth C. Schiff

Catherine Wright

John F. Griffith

Sukhminder K. Sandhu

Stephen B. Weisberg

Southern

California Coastal Water Research

Project

Established 1969

 

 


 

Recreational Water 

Contact and Illness in 

Mission Bay, California

Southern California CoastalWater Research Project 
Recreational Water Contact and 

Illness in Mission Bay, 

California 

John M. Colford, Jr. 1

Timothy J. Wade2

Kenneth C. Schiff3

Catherine Wright1

John F. Griffith3

Sukhminder K. Sandhu1

Stephen B. Weisberg3

1

University of California Berkeley 

School of Public Health 

140 Warren Hall 

Berkeley, CA 94720 

2

Southern California Coastal Water Research Project 

7171 Fenwick Lane 

Westminster, CA 92683 

3

United States Environmental Protection Agency 

National Health and Environmental Effects Research Laboratory 

Research Triangle Park, NC 27711 

March 11, 2005 

Technical Report #449 
Recreational Water Contact and Illness in Mission Bay California 

i

FOREWORD 

This investigation was a collaboration between the Southern California Coastal Water 

Research Project and the University of California, Berkeley School of Public Health. 

This project was funded by the City of San Diego through a Supplemental Environmental 

Project (ACL No.2001-094) and the San Diego Regional Water Quality Control Board 

through the Clean Up and Abatement Fund (SWRCB Contract No. 02-166-190-0). The 

conclusions represent those of the authors and are not necessarily the position of the City 

of San Diego, the State of California, or the U.S. Environmental Protection Agency (U.S. 

EPA). Mention of trade names does not constitute an endorsement by the City of San 

Diego or the State of California. 
Recreational Water Contact and Illness in Mission Bay California 

ii

ACKNOWLEDGEMENTS

We would like to thank the many organizations that helped with data collection and/or 

sample processing on this project. Fecal indicator bacterial analysis using traditional 

methodologies was coordinated by Ric Amador and Laila Othman at the City of San 

Diego Metropolitan Wastewater Department Microbiology Laboratory (San Diego, CA). 

Rich Haugland and Al Dufour of the U.S. EPA provided the protocols and some filtration 

equipment for analysis of enterococcus and Bacteroides using quantitative polymerase 

chain reaction (QPCR). The QPCR was conducted by Charles LaCerra of EMSL, Inc. 

(Westmont, NJ). Virus and coliphage measurements were coordinated by Mark Sobsey 

of the University of North Carolina (Chapel Hill, NC). The human health data collection 

was coordinated by Susan Burns and Jackie Hayes at the UC Berkeley Survey Research 

Center (Berkeley, CA). Data management and analytic support were provided in part by 

Srikesh Arunajadai and Shannon Carr at the UC Berkeley School of Public Health. 

The authors also wish to acknowledge the invaluable guidance provided by the 

independent scientists of the project Steering Committee (in alphabetical order): 

 

Rebecca Calderon United States Environmental Protection Agency 

Richard Gersberg San Diego State University 

Michele Ginsberg San Diego County Department of Environmental Health 

Mark Gold Heal the Bay 

Charles McGee Orange County Sanitation District 

John Witte University of California, San Francisco 

We would also like to acknowledge the support of our contract managers, Christina Arias 

and Leslie Dobalian, from the San Diego Regional Water Quality Control Board; and 

advice from Ruth Kolb from the City of San Diego and Clay Clifton from the San Diego 

County Department of Environmental Health. 
Recreational Water Contact and Illness in Mission Bay California 

iii

ABSTRACT

Fecal indicator bacteria are routinely monitored at marine recreational bathing beaches to 

assess the public health risk of contracting swimming-related illness. There have been 

numerous epidemiology studies that demonstrated the relationship of indicator bacteria to 

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. 

Here, we present an epidemiology study conducted in Mission Bay, California, where 

nearly 20% of the historic routine bacterial samples failed water quality standards but the 

dominant fecal source appears to be non-human. The study focused 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 indicators of water 

quality? and (3) Among those individuals with water contact, were there associations 

between illness and measured levels of non-traditional indicators of water quality? 

The project was designed as a cohort study. Nearly 8,800 participants were recruited 

from the six most popular swimming beaches in Mission Bay on weekends and holidays 

during the summer of 2003. Each participant provided their current state of health and 

degree of water exposure on their day at the beach. On the same day, water quality was 

monitored for traditional fecal indicator bacteria (enterococcus, fecal coliforms, total 

coliforms). A subset of samples was also measured for non-traditional indicators, 

including new methods for measuring traditional indicators (chromogenic substrate or 

quantitative polymerase chain reaction [QPCR]), new bacterial indicators (Bacteroides), 

and viruses (somatic and male-specific phage, adenovirus, Norwalk-like virus). 

Ten to 14 days later, the participants were contacted by phone and interviewed about 

symptoms of illness that occurred since their visit to the beach. They were queried about 

multiple types of illness: gastrointestinal illnesses (diarrhea, nausea, stomach pain, 

cramps, vomiting, highly credible gastrointestinal illness 1 or 2 [HCGI-1 or HCGI-2]); 

respiratory illnesses (cough, cough with phlegm, nasal congestion or runny nose, sore 

throat, significant respiratory illness); dermatologic outcomes (skin rash, infected cuts or 

scrapes); and non-specific symptoms (fever, chills, eye irritation, earache, ear discharge, 

eye irritation or redness). Multivariate analysis was conducted to assess relationships 

between health outcomes and degree of water contact or levels of water quality 

indicators. These analyses were adjusted for confounding covariates such as age, gender, 

and ethnicity. 

Of the measured health outcomes, only skin rash and diarrhea were consistently 

significantly elevated in swimmers compared to non-swimmers. For diarrhea, this risk 

was strongest among children 5 to 12 years old. The risk of illness was uncorrelated with 

levels of traditional water quality indicators. Of particular note, the state water quality 

thresholds were not predictive of swimming-related illnesses. Similarly, no correlation 
Recreational Water Contact and Illness in Mission Bay California 

iv

was found between increased risk of illness and increased levels of most non-traditional 

water quality indicators. A significant association was observed between the levels of 

male-specific coliphage and HCGI-1, HCGI-2, nausea, cough, and fever, but we interpret 

these associations cautiously because so few participants were exposed to the water at 

times when male-specific coliphage was detected. 

While we found that traditional fecal indicators were ineffective predictors of health 

effects, it is difficult to extrapolate this finding beyond Mission Bay. Mission Bay is 

unusual in that it has been subjected to thorough cleanup activities that source tracking 

studies confirm leave human fecal sources as only a minor contributor. Moreover, 

Mission Bay has an unusually long hydraulic residence time compared to other coastal 

systems, which affects the age and viability of waterborne fecal material. This study, 

though, does suggest the need for further evaluation of traditional indicators in 

circumstances where non-point sources are the dominant fecal contributors. 
Recreational Water Contact and Illness in Mission Bay California 

v

Table of Contents 

page 

Foreword........................................................................................................................ i 

Acknowledgements....................................................................................................... ii 

Abstract........................................................................................................................ iii 

INTRODUCTION........................................................................................................1 

MATERIALS AND METHODS ................................................................................3 

 Sampling Sites .........................................................................................................3 

 Water Quality Data Collection.................................................................................4 

 Laboratory Methods...........................................................................................5 

 Epidemiological Data Collection.............................................................................6 

 Beach recruitment..............................................................................................7 

 Follow-Up CATI Interview ................................................................................7 

 Health Outcomes Measured...............................................................................7 

 Data Analysis...........................................................................................................8 

 Water Quality.....................................................................................................8 

 Epidemiology .....................................................................................................8 

RESULTS ...................................................................................................................11 

 Water Quality.........................................................................................................11 

 Traditional fecal indicator bacteria.................................................................11

 Non-traditional fecal indicator bacteria..........................................................13

 Virus Measurements.........................................................................................14 

 Effectiveness of compositing............................................................................15 

 Epidemiology.........................................................................................................17 

 Health Outcomes for Swimmers versus Non-swimmers ..................................18 

 Relationship between Health Outcomes and Water Quality............................25 

Time in Water...................................................................................................27

DISCUSSION .............................................................................................................28 

STUDY CONCLUSIONS..........................................................................................30 

LITERATURE CITED .............................................................................................32 

APPENDICES............................................................................................................35 
Recreational Water Contact and Illness in Mission Bay California 

1

INTRODUCTION 

Fecal indicator bacteria are monitored routinely at marine recreational bathing beaches to assess 

the public health risk of contracting swimming-related illnesses. In southern California, more 

than 85,000 samples are collected and over $3 million is spent annually to assess public health 

risk using these bacterial tests as indicators of fecal contamination (Schiff et al. 2002). The focus 

on bacteria as a public health monitoring tool is predicated on the relationship between the 

density of fecal indicator bacteria and the occurrence of illnesses in the swimming population. 

Numerous studies have demonstrated the relationship between fecal indicator bacteria at beaches 

and the occurrence of swimming-related illnesses (Prüss 1998, Wade et al. 2003). Prominent 

among these studies are Cabelli (1979 and 1983) who observed a relationship between 

enterococcus and illness rates at several beaches around the country, and Haile et al. (1999) who 

observed an increase in swimming-related illnesses and enterococcus, fecal coliforms, and total 

coliforms at beaches in Santa Monica Bay, California. These studies were the focal point for the 

establishment of water quality thresholds at marine beaches using fecal indicator bacteria in the 

United States and the State of California, respectively. 

While these previous epidemiology studies successfully demonstrated the value of fecal indicator 

bacteria, virtually all of these studies were conducted at locations where human sewage was the 

predominant contamination source. Haile et al. (1999) was the only study to have focused on 

urban runoff as a source, but even this non-point source was known to contain human sources of 

fecal contamination. Most of the beach water quality problems in California are attributable to 

non-point source runoff (Noble et al. 2003, Schiff et al. 2003), and it is less clear that the health 

relationships for bacterial indicators will remain the same when non-human sources predominate 

(Calderon et al. 1991). Since animals shed bacterial indicators without some of the 

accompanying human pathogens, there is considerable uncertainty in extrapolating present water 

quality thresholds that are based on the risk of swimming-associated illnesses to non-point 

source situations. A poor correlation between bacterial indicators and virus concentrations has 

been found when examining urban runoff (Jiang et al. 2001, Noble and Fuhrman 2001), in 

contrast to the significant relationships that have been found when examining water bodies 

influenced by human sources, such as septic tanks (Lipp et al. 2001). 

Here, we present an epidemiology study conducted in Mission Bay, California, where 

state water quality standards have historically been exceeded more than 20% of the time (Schiff 

and Kinney 2002). Several million dollars have been expended to remove human contamination 

from the Mission Bay by inspecting and repairing the sanitary sewerage system surrounding the 

bay and diverting the largest storm drains away from the bay. As a result, recent source tracking 

studies suggest that human fecal material constitutes a minor proportion of fecal inputs to the 

Bay (City of San Diego and MEC/Weston 2004). However, exceedances of California’s water 

quality standards continue to occur (Hanley 2002). 

The goal of this study was to examine the health effects of swimmers and their relationship to 

water quality indicators in this system where non-human fecal sources are dominant. The study 

attempted to answer two primary questions: 
Recreational Water Contact and Illness in Mission Bay California 

2

• Did water contact increase the risk of illness in the two weeks following exposure to 

water in Mission Bay during the summer of 2003? 

• Among those individuals with water contact, were there associations between illness and 

measured levels of traditional indicators of water quality? 

In addition, we addressed a third question about whether there were associations between illness 

and measured levels of several nontraditional indicators of water quality. New laboratory 

methods, particularly nucleic acid-based methods, are promoted as monitoring tools because they 

are faster, cheaper, or more specific than traditional methods of measuring fecal indicator 

bacteria that rely on culture- or growth-based endpoints. The efficacy of any new public health 

monitoring tool can only be evaluated through an epidemiological study that documents its 

relationship to the incidence of swimming-related illness. 

Specifically, we tested a rapid method for measuring bacteria and several measures of viruses. 

Whereas traditional measurement methods for bacteria are slow (> 18 hrs), we included a nucleic 

acid-based technique that provides results in less than four hours (Noble and Weisberg et al. In 

Press). Similarly, virus measurements have been an inefficient monitoring tool to date because 

of inefficient recovery methods, expense of detection methods, and length of time for obtaining 

results. Culture–independent, nucleic acid-based techniques allow measurements that are faster, 

less costly, and more specific. These methods have not been previously evaluated in an 

epidemiology study. 
Recreational Water Contact and Illness in Mission Bay California 

3

MATERIALS AND METHODS 

This project was designed as a cohort study (NRC 2004). Six of the most popular swimming 

beaches in Mission Bay were targeted every weekend and holiday from Memorial Day to Labor 

Day during the summer of 2003. Participants were recruited each sampling day and, after giving 

consent, their current state of health and degree of exposure to the water were recorded. Water 

quality was measured at multiple sites and over multiple time periods on the same days as the 

epidemiological data. Ten to 14 days later, the participants were contacted by phone and 

interviewed about symptoms of illness that occurred after their visit to the beach. The resulting 

data were tested for significant differences in illness between swimmers and non-swimmers. 

Among the participants that swam, the probability of illness was regressed against various 

measures of water quality exposure. The specific methods used in this study are described below 

and are organized into four sections: sampling sites, water quality data collection, 

epidemiological data collection, and data analysis. 

Sampling Sites 

The study sites were selected based on a pilot study conducted in the summer of 2002. Aerial 

photography, supplemented with on-the-beach enumeration of swimmers for groundtruthing (to 

confirm the findings of the aerial survey), was used to identify the locations and times of greatest 

swimmer activity. Hourly images from 9:00 AM to 6:00 PM were collected on 10 days at 10 

different swimming areas in Mission Bay. The pilot study identified the most effective times and 

locations for maximizing the number of potential study participants. 

Recruitment of beach-goers occurred at six Mission Bay beaches on weekends and holidays, 

beginning Memorial Day weekend and continuing through Labor Day weekend, 2003 (Figure 1). 

Recruitment took place between 12:00 PM and 4:00 PM each weekend day. Water quality 

samples were collected at the same six beaches. A total of 18 sites were targeted, with the 

number of sites per beach ranging from two to five, depending upon the length of beach and 

anticipated swimming activity (Table 1). Data were collected on 29 of 32 targeted sampling 

dates; three days were excluded from sampling (June 9, 17, and 18, 2003) due to inclement 

weather and significantly reduced beach usage. 

Figure 1. Map of study sites.
Recreational Water Contact and Illness in Mission Bay California 

4

Table 1. Study sites used for water quality sampling 

during the Mission Bay epidemiology study. Latitude 

and longitude in NAD83 datum. 

Beach Site Number Latitude Longitude 

Visitor Center 1 32.47.19N 117.12.55W 

Visitor Center 2 32.47.30N 117.12.54W 

Tecolote Shores 1 32.46.34N 117.12.54W 

Tecolote Shores 2 32.46.46N 117.12.61W 

Tecolote Shores 3 32.46.61N 117.12.66W 

Leisure Lagoon 1 32.47.02N 117.12.67W 

Leisure Lagoon 2 32.46.93N 117.12.62W 

Leisure Lagoon 3 32.46.96N 117.12.58W 

Leisure Lagoon 4 32.47.07N 117.12.55W 

Leisure Lagoon 5 32.47.15N 117.12.58W 

De Anza 1 32.47.81N 117.12.71W 

De Anza 2 32.47.80N 117.12.78W 

Crown Point 1 32.47.36N 117.13.86W 

Crown Point 2 32.47.24N 117.13.85W 

Crown Point 3 32.47.15N 117.13.90W 

Bonita Cove 1 32.46.12N 117.14.72W 

Bonita Cove 2 32.46.17N 117.14.79W 

Bonita Cove 3 32.46.16N 117.14.89W 

Water Quality Data Collection 

Twelve types of water quality measures were collected during this study. Three were traditional 

indicators (enterococcus, total coliforms, fecal coliforms) measured by traditional methods 

(membrane filtration [MF]). Three were the same indicators measured using the newer 

chromogenic substrate (CS) method. One was enterococcus measured by a new method, 

quantitative polymerase chain reaction (QPCR). The final five were new indicators 

(Bacteroides, somatic coliphage, male-specific coliphage, adenovirus, and Norwalk-like virus). 

Water quality samples were collected at one of three temporal intensities, depending on 

indicator, which was necessitated by differences in sample volume, laboratory effort, and cost of 

the various methods (Table 2). The greatest sampling intensity occurred at all 18 sites hourly 

from 12:30 PM to 3:30 PM. These samples were analyzed by MF for total and fecal coliforms, 

and for enterococcus using the CS method. The second sampling intensity was also at all 18 

sites, but only twice daily (12:30 PM and 2:30 PM). These samples were analyzed for 

enterococcus and Bacteroides spp. using QPCR. The third sampling intensity was a composite 

sample at each beach, once daily. The composite samples were comprised of the individual sites 

within each beach at the 12:30 PM sampling interval. These samples were analyzed for total and 

fecal coliforms (E. coli) using CS, enterococcus using MF, somatic and male-specific phage, and 

adenovirus and Norwalk-like virus. 

Samples for analysis of total coliforms, fecal coliforms, and enterococcus were collected in 125 

mL sterilized high-density polyethylene (HDPE) bottles. Composite samples for these 
Recreational Water Contact and Illness in Mission Bay California 

5

constituents were created by pouring the 125 mL HDPE bottles into a single 500 mL sterilized 

HDPE bottle. Samples for phage were collected in 1L sterilized HDPE bottles, while samples 

for analysis of virus were collected in 5 x 4L cubitainers. All samples were placed on ice in the 

dark and transported to the laboratory for processing within six hours. Sample analysis for total 

coliforms, fecal coliforms, and enterococcus was initiated within the six-hour holding time for 

these measurements. 

Samples for Bacteroides and enterococcus QPCR analysis were collected as described by 

Brinkman et al. (2003). Samples for QPCR adenovirus and Norwalk-like virus were first 

amended with 50mM final concentration MgCl before being passed through glass fiber filters 

(GF/F) (Whatman, Clifton, NJ) using positive pressure. Following concentration, all filters were 

stored at –80°C until shipment to the analytical laboratory. Frozen filters were shipped to the 

laboratory in a cryoshipper containing liquid nitrogen to maintain the integrity of the nucleic acid 

material. Water samples for phage analysis were stored overnight at 4°C before shipment to the 

laboratory on ice via overnight express. 

Laboratory Methods

Enterococcus was measured using three different techniques. Individual samples from each site 

were measured using EnterolertTM chromogenic substrate and the Quantitray 2000TM system 

(IDEXX Westbrook, ME), while composite samples were measured using the 24-hour EPA 

Method 1600 (m-EI). The third technique used to measure enterococcus was QPCR (Brinkman 

et al. 2003). Unlike the membrane filtration or chromogenic substrate techniques that rely on 

growth-based endpoints, QPCR relies on amplification of unique DNA sequences to estimate the 

number of bacterial cells in the original sample (Brinkman et al. 2003; Haugland. In press). This 

technique is currently being used by the U.S. EPA in their National Epidemiology Study. 

Total coliforms and fecal coliforms were measured using two different techniques. In individual 

samples, total and fecal coliforms were enumerated by membrane filtration using APHA Method 

9222B (m-Endo) and APHA Method 9222D (M-FC), respectively. In composite samples, total 

and fecal coliforms (E. coli) were enumerated using Colilert-18TM chromogenic substrate and 

Quantitray 2000TM system (IDEXX, Westbrook, ME). 

The QPCR method also was used to measure Bacteroides, a group of fecal obligate anaerobic 

bacteria that cannot survive for extended periods in oxygenated environments (Bernhard and 

Field 2000; Bernhard et al. 2003). Measurements of this indicator were performed 

simultaneously with QPCR measurements of enterococcus. 

F+ and somatic coliphages were detected and quantified in 1 L volumes of water by a 

modification of USEPA Method 1601 for enrichment and spot-plating that provides a Most 

Probable Number (MPN) estimate of coliphage concentration. One-liter sample volumes were 

supplemented with 0.05M MgCl2, host bacteria were added (E. coli Famp for F+ coliphages or 

E. coli CN-13 for somatic coliphages), the sample was quickly divided into aliquots of three 

replicate volumes each of 300, 30, and 3 mL, and these volumes were enriched overnight at 

36°C. A small volume of each enrichment culture was spotted onto an agar medium lawn of 

host bacteria and incubated for 4 hours at 36°C and scored for the presence of coliphages. The 

number of enrichment cultures that were positive for coliphages were used to compute an MPN 

concentration. 
Recreational Water Contact and Illness in Mission Bay California 

6

Analysis of Norwalk-like viruses and adenoviruses on GF/F filters was conducted by molecular 

methods. Three-quarter pieces of the first 75% of frozen filters with DNA concentrates were 

eluted and extracted using 1.5% beef extract elution, PEG precipitation, and viral-NA 

extraction/purification using GITC lysis buffer and Qiagen midi columns, followed by ethanol 

precipitation. A 2.5 μl volume of the final 50 μl of total concentrate was analyzed using seminested PCR. A one-ninth portion of the remaining 25% frozen Whatman GF/F filters was eluted 

and extracted using lysis buffer directly, followed by purification using the Qiagen plant kit. Of 

the final 50 μl volume of nucleic acid extract, 5 μl (10%) was used for (RT)-PCR analysis of 

each virus (human adenovirus, genogroup I norovirus, and genogroup II norovirus. 

Table 2. Methods, analytical laboratories, and sampling intensity used for water quality 

measurements during the Mission Bay Epidemiology Study. 

Parameter Method Analytical 

Laboratory 

Sampling intensity 

Enterococcus EPA 1600 City of San Diego Beach composite once per day

Enterococcus 96 well Quantitray City of San Diego Hourly sample at every site 

Enterococcus Quantitative PCR EMSL Two samples per day at each 

site 

Fecal Coliforms APHA Method 

9222D 

City of San Diego Hourly sample at every site 

Fecal Coliforms (E. coli) 96 well Quantitray City of San Diego Beach composite once per day

Total Coliforms APHA Method 

9222B 

City of San Diego Hourly sample at every site 

Total Coliforms 96 well Quantitray City of San Diego Beach composite once per day

Bacteroides Quantitative PCR EMSL Two samples per day at each 

site 

Somatic Phage Modified EPA 1601 University of North 

Carolina 

Beach composite once per day

Male-specific Phage Modified EPA 1601 University of North 

Carolina 

Beach composite once per day

Adenovirus 40 and 41 Quantitative PCR University of North 

Carolina 

Beach composite once per day

Norwalk-like Virus Quantitative PCR University of North 

Carolina 

Beach composite once per day

 

Epidemiological Data Collection 

Three study instruments were developed for this project including: (1) an intervieweradministered screening form to assess eligibility and desire to participate; (2) a self-administered 

questionnaire (SAQ) that was completed by study subjects before they left the beach for the day; 

and (3) a computer-aided telephone interview (CATI) questionnaire administered to study 

participants approximately two weeks following their visit to a Mission Bay beach (Appendix 1). 

The study instruments, in addition to the study protocol and consent form, were approved by the 

Committee for the Protection of Human Subjects at U.C. Berkeley prior to study initiation. 
Recreational Water Contact and Illness in Mission Bay California 

7

Beach Recruitment 

Interviewers canvassed the study beaches, approaching individuals and groups to determine their 

interest in and eligibility to participate in the study. Eligibility criteria included: (1) no previous 

participation in the study; (2) at least one family member of the household at the beach was 18 

years old or older; (3) home address in the United States, Canada, or Mexico (interviews were 

conducted in either English or Spanish); and (4) had not swam (face or head under water) in the 

ocean or in a lake in the previous seven days. If an individual or household was eligible and 

agreed to participate, the interviewers obtained signed consent from the individual or all 

participating adult members of the household. Adults gave signed consent for children under 18. 

Participants were then asked for their names, their contact information, and their city and state of 

residence. The household data also contained the background variables of the recruited 

households, including household size and the language that was used to obtain consent. During 

the screening process, each participant was assigned a non-informative identification code. 

Interviewers marked the screening form to identify the water quality sampling site that 

corresponded best with the location of the individual or family on the beach. Participants were 

given an incentive (beach ball) and asked to complete the SAQ prior to their departure that day. 

The SAQ consisted of 18 questions concerning possible exposures at the beach (i.e., swimming, 

other activities, food and beverages, other exposures) and exposures or illnesses experienced 

during the 2-3 days prior to the beach visit. The survey took no longer than 15 minutes to 

complete. Participants who failed to complete the survey at the beach were contacted within 

three days by telephone interviewers, and their surveys were completed over the phone. 

Participants that completed the survey at the beach were given additional incentives (water 

bottles and beach balls). 

Follow-Up CATI Interview 

Between 10 and 14 days following their beach visit, participants were telephoned and asked to 

complete a 10- to 15-minute interview. This interview consisted of the following types of 

questions: (1) demographic information, including race, income, education level; (2) swimming 

and other exposures since the interview day; (3) existing health problems potentially related to 

the study outcomes (e.g., chronic diarrhea); and (4) acute health conditions (gastrointestinal, 

respiratory, skin, eye, or ear) experienced since the visit to the beach. If acute illnesses were 

experienced, a series of questions were asked to determine whether the subject had to restrict 

normal activities (missed work or school, or other activities) and whether they visited a doctor, 

clinic, or other medical facility for the illness. As with the previous interviews, the head of 

household answered questions for children under 18. 

Health Outcomes Measured 

The health outcomes quantified through the CATI interview included gastrointestinal illness, 

respiratory symptoms, dermatologic symptoms, and other non-specific symptoms. 

Gastrointestinal illness included nausea, vomiting, diarrhea, and stomach pains or cramps. In 

addition, two categories of highly credible gastrointestinal illness (HCGI) were measured. 

HCGI-1 was defined as either: (1) vomiting plus diarrhea or fever; or (2) cramps and fever. 

HCGI-2 was defined as vomiting plus fever. Respiratory outcomes included cough, cough with 

phlegm, nasal congestion or runny nose, sore throat, and significant respiratory disease (SRD). 

SRD was defined as: (1) fever plus nasal congestion; or (2) fever plus sore throat; or (3) cough 

with phlegm. Dermatologic outcomes included skin rashes and infected cuts or scrapes. Non-
Recreational Water Contact and Illness in Mission Bay California 

8

specific symptoms included fever, chills, redness or eye irritation, earache, and ear discharge or 

drainage. 

Data Analysis 

Water Quality

Water quality analysis focused on assessment of swimmer exposure, including: (1) identification 

of the ranges of fecal indicator bacteria densities among beaches; (2) determining whether the 

compositing strategy within a beach adequately represented the beach average as determined by 

individual samples at multiple sites across a beach; and (3) correlating the different indicator 

organisms and methods to ascertain if the densities were providing redundant or unique 

information relative to swimmer exposure. 

Epidemiology

Two principal epidemiological analyses were conducted. The first was a model to evaluate 

whether there was a significant difference in illness rate between swimmers and non-swimmers. 

Swimming risk (i.e., swimmers compared to non-swimmers) was contrasted for multiple 

definitions of “swimming,” including: “any water contact,” “water up to the shoulder,” “water on 

the face,” “face under the water,” “water in the mouth,” and “swallowed water.” These 

definitions were designed to reflect qualitatively different levels of exposure to the water. 

The second analysis was a model that examined whether there was a significant relationship 

between the risk of illness in swimmers and water quality (as measured water quality indicators). 

These models were constructed for each of the measured water quality indicators using 

numerous approaches for swimmer exposure, including incremental changes for daily geometric 

mean for all sites at a beach, daily geometric mean for the site(s) nearest the swimmer, and 

geometric mean for just those site(s) and time(s) nearest the swimmer. Additionally, state water 

quality thresholds for enterococcus were examined using dichotomous cutpoints (>35 vs. < 35 

and >104 vs. < 104) for evaluating risk. In all models involving indicators, a value of zero was 

used for water quality exposure values below the detection limit. 

All analyses were conducted as both univariate and multivariate models. The multivariate 

models included potential confounding factors as covariates. The covariates examined were age 

category (0-5, 5-12, 12-30, >30), gender, ethnicity, allergies, history of swimming again after the 

beach interview, history of collecting shells at the beach, history of digging or having one’s body 

buried in the sand, history of playing with seaweed or algae, history of chronic illnesses 

(gastrointestinal, asthma, or chronic skin conditions), contact with other sick people, use of 

insect repellant at the beach, use of sunblock at the beach, history of showering immediately 

after swimming, consumption of raw or undercooked eggs or meat, income, and consumption of 

food while at the beach. All variables, except age, were categorized as 1 or 0. Race was 

collapsed into two categories, white and non-white. 

All analyses were conducted using the same basic model that is being used in the U.S. EPA 

BEACHES study. This is a nested interaction model that allows linear combinations of variables 

to be estimated. This permits comparisons among swimmers while retaining non-swimmers in 

the model, as well as comparisons among swimmers versus non-swimmers. The components of 

the model are: 
Recreational Water Contact and Illness in Mission Bay California 

9

 p = probability of illness 

 (NOTE: “ p / (1-p) “ defines the odds of illness 

 X1=1 if any contact with water; 0 otherwise 

 X2 is the water quality measure 

 X3 is a 1/0 indicator of other exposure (body contact, head under water, etc.) 

 Non-swimmers=α

 (NOTE: The model reduces to ln (odds) = α when all other variables are set equal to 

“0”, i.e., the situation representing non-swimmers. 

 Swimmers-any contact=α+β1x1+β2(x1*x2) 

 Swimmers-other contact=α+β1x1+β2(x1*x2) +β3x3+β4(x3*x2) 

In the multivariate analyses, a backwards deletion procedure (Rothman and Greenland 1998) was 

used to identify factors that most affected the water quality/illness relationship. This procedure 

uses the following algorithm: 

(1) The full model is fit with all covariates. 

(2) The estimate of interest is saved (e.g., coefficient for association between water 

quality and illness) 

(3) The first covariate in the list is removed, and then the model is refit 

(4) The estimate of interest is saved. 

(5) The percentage change between the estimate in Step 2 and the estimate in Step 4 is 

calculated. 

(6) The procedure is repeated for all covariates in list 

(7) After all models have been fit, determine the covariate that had the smallest impact on 

the water quality/illness relationship (i.e., the smallest percent change). This covariate 

is removed completely. 

(8) Repeat Steps 3-7 until removal of any single additional covariate produces a change 

greater than 10% (or some other pre-specified criterion) in the fully adjusted water 

quality/illness relationship. In this study, a change greater than 10% was used as the 

criterion for stopping the removal of covariates. 

The advantage of this procedure is that it focuses on the exposure/outcome relationship and 

selects the covariates that are the strongest confounders of this key relationship. This is in 

contrast to traditional stepwise procedures that focus on the significance, or strength, of the 

association between the covariate and the outcome (rather than the association between the 

exposure and the outcome). The disadvantage is that each model can require extremely long 

times to complete. For example, many of the models required more than one week to complete 

(running 24 hours/day). 

ln( ) /( ) 1 ( * ) ( * ) 1 1 2 1 2 3 3 4 3 2 p − p =α + β x + β x x + β x + β x x
Recreational Water Contact and Illness in Mission Bay California 

10

 

The risk of illness output from the models was expressed as an odds ratio. For models comparing 

swimmers and non-swimmers, the odds ratio can be interpreted as the odds of a specific illness 

in swimmers divided by the odds of illness in non-swimmers. Odds ratios (statistically) 

significantly greater than 1.0 are indicative of illness elevated for swimmers compared to nonswimmers. For models assessing the association between water quality among swimmers, the 

odds ratios can be interpreted as the increase in the odds of illness per defined unit of increase in 

the water quality measure among swimmers. The odds ratios were calculated by exponentiating 

the regression coefficient provided by the model output. 

Attributable risk calculations were performed for health outcomes that were significantly 

increased in swimmers compared to non-swimmers. Attributable risk is a measure of excess 

risk. For this study, models adjusted for relevant covariates (see above) were used to estimate 

the percentages of swimmers and non-swimmers ill for any health outcomes with a statistically 

significant elevated adjusted odds ratio. The adjusted attributable risk estimates were determined 

by estimating adjusted probabilities of swimmers and non-swimmers from a multivariate logistic 

model, weighting the covariates at the mean value for each covariate. The adjusted attributable 

risk was then calculated as the difference between the probability of illness among swimmers 

with mean levels of covariates and non-swimmers with mean levels of covariates. These results 

are expressed as the number of excess cases of illness seen among 1,000 swimmers (along with a 

95% confidence interval of this estimate). 

Emphasis is placed on the multivariate (adjusted) results throughout the report because they 

correct for confounding from substantial differences in ethnicity, age, beach, and other covariate 

distributions. The univariate results, though, are provided in Appendices 2 and 3 for the adjusted 

odds ratios and attributable risk calculations. 
Recreational Water Contact and Illness in Mission Bay California 

11

RESULTS

Water Quality 

A total of 1,897 water samples were collected during the survey, with the sampling schedule and 

number of samples differing among microbial indicators (Table 3). All intended samples were 

collected, with the exception of those on June 9, 17, and 18, when drizzle led to a lack of 

swimmers and sampling was curtailed. With the exception of one sample for traditional 

indicators that was spilled and four virus samples that were compromised in the freezing/thawing 

process, every sample collected was analyzed successfully in the laboratory. 

Table 3. Number of samples processed for each beach by indicator type. 

Beach Traditional Fecal 

Indicators 

PCR-based Fecal 

Indicators 

Phage Virus 

Bonita Cove 324 131 25 24 

Crown Point 324 132 23 22 

De Anza Cove 207 88 26 25 

Leisure Lagoon 539 219 24 23 

Tecolote Shores 304 132 24 24 

Visitors Center 200 88 24 23 

Total 1897 790 151 141 

Traditional fecal indicator bacteria 

A wide range of traditional bacterial densities were measured over the course of the study (Table 

4). The majority of samples had quantifiable levels of enterococcus, fecal coliform, and total 

coliform; between 16% and 40% of the samples were below the method detection limits, 

depending upon the indicator. Maxima for all three bacterial indicators ranged to 105

MPN/100mL. About 16% of all samples that measured traditional fecal indicator bacteria 

exceeded state water quality thresholds, with enterococcus accounting for most of the 

exceedances (96%) and total coliforms the least (2%). 

Table 4. Range of concentrations for traditional water quality indicators (number/100 mL) and 

frequency of exceedance (N=1,897) of the State of California’s water quality threshold. 

 No. of 

Samples 

Below RL 

Geomean Maximum No. of Samples 

Exceeding 

Threshold 

State Water 

Quality 

Threshold 

EnterococcusCS 585 29 57,940 265 >104 

Fecal Coliform 304 25 48,000 99 >400 

Total Coliform 808 102 45,000 5 >10,000 

Total:Fecal Ratio - - - 75 Total:Fecal < 10 

WhenTotal > 1,000

The lowest average concentrations occurred at Crown Point (Figure 2), where less than 6% of the 

enterococcus values exceeded state water quality thresholds. The highest densities of 
Recreational Water Contact and Illness in Mission Bay California 

12

0 20 40 60 80 100

Enterococcus (MPN/100 mL)

100

101

102

103

104

105

106

0 20 40 60 80 100

Fecal Coliform (MPN/100 mL)

100

101

102

103

104

105

Bonita Cove

Crown Point

DeAnza Cove

Leisure Lagoon

Tecolote Shores

Visitors Center

Percent of Samples

0 20 40 60 80 100

Total Coliform (MPN/100 mL)

100

101

102

103

104

105

Figure 2. Cumulative distribution frequency for enterococcus, fecal coliform, 

and total coliform by study beach. The horizontal line indicates the state’s 

water quality threshold (see table 4). 
Recreational Water Contact and Illness in Mission Bay California 

13

enterococcus were observed at Leisure Lagoon with maximum densities reaching 57,940 

MPN/100mL. The greatest frequency of water quality exceedances occurred at Bonita Cove. 

More than 21% of the samples collected at this beach exceeded state water quality thresholds. 

Non-traditional fecal indicator bacteria

A wide range of non-traditional bacterial densities were measured over the course of the study 

(Table 5). The majority of samples had quantifiable levels of enterococcus and Bacteroides, 

with 6% and 37% of the samples below method detection limits, respectively. Maxima for both 

bacterial indicators ranged from 105

 to 106 MPN/100mL. For enterococcus, 42% of samples 

exceeded the state water quality threshold. There is no state water quality threshold for 

Bacteroides. 

Table 5. Range of concentrations (number/100 mL) for non-traditional fecal indicator bacteria. 

QPCR = quantitative polymerase chain reaction. 

 No. of 

Samples 

Below RL 

Geomean Maximum No. of 

Samples 

Exceeding 

Threshold 

State Water 

Quality 

Threshold 

Enterococcus-QPCR 46 65 141,053 351 >104 

Bacteroides 294 102 3,718,815 - - 

Only minimal correlation was found among traditional and non-traditional fecal indicator 

bacteria indicators (Table 6). The best relationships were among the traditional indicator 

bacteria, particularly the coliform groups. The worst relationships were for Bacteroides, which 

might be expected since they are functionally a different group of microorganisms. For 

enterococcus, the relationship between the growth-based assay and the nucleic acid-based 

technology was not strong (Figure 3). QPCR overestimated the enterococcus density compared 

to the growth-based assays, possibly due to the presence of non-viable DNA, which are only 

measured by PCR. 

Table 6. Correlation coefficients between traditional and non-traditional fecal indicator bacteria. 

CS= chromogenic substrate; QPCR = quantitative polymerase chain reaction. 

 Fecal Coliform 

EnterococcusCS EnterococcusQPCR Bacteroides 

Total Coliform 0.51 0.40 0.28 0.01 

Fecal Coliform 0.35 0.17 0.01 

Enterococcus–CS 0.24 0.24 

Enterococcus–QPCR 0.01 
Recreational Water Contact and Illness in Mission Bay California 

14

Enterococcus by Chromogenic Substrate (MPN/100 mL)

101 102 103 104

Enterococcus by PCR (Estimated/100 mL)

10-1

100

101

102

103

104

105

106

Figure 3. Comparison between enterococcus using traditional growth-based assay (chromogenic 

substrate) versus the non-traditional nucleic acid-based (QPCR) technology. 

Virus Measurements 

Virtually no pathogenic virus was detected in the samples collected from Mission Bay over the 

course of the study (Table 7). There were no detectable Norwalk-like virus and only a single 

sample detected for adenovirus. The majority of samples had quantifiable levels of somatic 

phage, but not for male-specific phage, which is more strongly associated with human fecal 

material (Figure 4). Roughly 68% of the samples had detectable levels of somatic phage and 

maximum concentrations were observed near 36 MPN/100 mL. Male-specific phage was 

detected in 11% of the samples and maximum concentrations reached only 1 MPN/100 mL. 

Table 7. Range of concentrations (number/100 mL) for virus measurements. 

 Total No. of 

Samples 

No. of Samples Below 

RL 

Geomean Max 

Adenovirus 151 150 - 0.01 

Norwalk-like Virus 151 151 - - 

Male-specific 

Phage 

141 

125 0.2 0.78 

Somatic Phage 141 45 0.6 36.6 
Recreational Water Contact and Illness in Mission Bay California 

15

Percent of Samples

0 20 40 60 80 100

Phage (MPN/100 mL)

10-1

100

101

Somatic

Male Specific

Figure 4. Cumulative distribution frequency for somatic and male-specific phage in 

Mission Bay during the study. 

Effectiveness of compositing 

Comparisons of composite samples to averages of individual grab samples for a site indicated 

that compositing was effective in representing beach-wide water quality for enterococcus (Figure 

5). Compositing described 69% of the variability in the individual grab sample arithmetic means 

(r2 = 0.69), and the y-intercept closely approximated the origin. This relationship was considered 

quite reasonable considering laboratory duplicate analysis described 61% of the variability 

observed between paired laboratory analyses from the same sample container using the same 

(chromogenic substrate) method (r2

 = 0.61). Significant relationships existed for composite 

samples versus the arithmetic mean of individual grab samples (r2

 = 0.39) for the fecal coliforms. 

Fecal coliform comparisons may be hindered because the chromogenic substrate method 

quantifies E. coli while the membrane filtration quantifies the entire fecal coliform group. The 

weakest relationship between composite samples and the arithmetic mean of individual grab 

samples was for total coliform (r2 = 0.06). 

 
Recreational Water Contact and Illness in Mission Bay California 

16

Enterococcus

Chromogenic Substrate Mean (estimated/100mL)

100 101 102 103 104

Membrane Filtration 

Composite (cfu/100 ml)

100

101

102

103

104

Fecalcoliform/E. coli

Membrane Filtration Mean (cfu/100mL)

100 101 102 103 104

Chromogenic Substrate 

Composite (MPN/100 ml)

100

101

102

103

104

Total Coliform

Membrane Filtration Mean (cfu/100mL)

100 101 102 103 104 105

Chromogenic Substrate 

Composite (MPN/100 ml)

101

102

103

104

105

Figure 5. Comparison of compositing versus the arithmetic mean 

of individual grab samples for enterococcus, fecal coliform/E. 

coli, and total coliform. Composite and grab samples were 

analyzed using either the chromogenic substrate or membrane 

filtration methodologies. 
Recreational Water Contact and Illness in Mission Bay California 

17

Epidemiology 

A total of 12,469 individuals and 5,062 households were enrolled in the study. Of these, 8,797 

(71%) of the enrolled participants and 3,501 (69%) of the households completed the follow-up 

telephone interview (Tables 8 and 9). Fifty-seven percent (n=4,971) of those that completed the 

follow-up interview were swimmers, compared to 3,742 non-swimmers. Non-swimmers were 

largely comprised of teens and adults aged 12 and older. In contrast, swimmers were roughly 

evenly divided among age groups with the majority (n=1,461, 29%) being 5 to 12 years old. 

There were slightly more males (54%) than female (45%) participants, which remained similar 

among swimmer and non-swimmer categories. Participants were dominated by Hispanic (54%) 

and white (28%) ethnicities. 

Tabulations of participant responses (all beaches combined and separately by beach) to questions 

regarding sociodemographic characteristics, and exposures prior to, during, and following their 

visit to the beach can be found in Appendices 4, 5, 6 and 7, respectively. 

Table 8. Individual sociodemographic characteristics collected from study participants at all 

beaches from Mission Bay. 

 Surveyed Participants 

All Swimmers Non-swimmers Missing 

Characteristic (N = 8,797 ) (N = 4,971 ) (N = 3,742) (N = 84) 

n % n % n % n % 

Age 

0 - 5 1,214 13.8 870 17.5 326 8.7 18 21.4 

5.1 - 12 1,808 20.6 1,461 29.4 332 8.9 15 17.9 

12.1 - 30 2,366 26.9 1,215 24.4 1,127 30.1 24 28.6 

30.1 - 55 2,928 33.3 1,251 25.2 1,654 44.2 23 27.4 

>55 332 3.8 76 1.5 253 6.8 3 3.6 

Missing 149 1.7 98 2.0 50 1.3 1 1.2 

Gender 

Male 4,761 54.1 2,624 52.8 2,100 56.1 37 44.0 

Female 3,948 44.9 2,292 46.1 1,609 43.0 47 56.0 

Missing 88 1.0 55 1.1 33 0.9 0 0.0 

Race 0.0 

White 2,495 28.4 1,181 23.8 1,307 34.9 7 8.3 

African American 369 4.2 165 3.3 194 5.2 10 11.9 

American Indian/Alaskan 

 Native 62 0.7 35 0.7 27 0.7 

Asian/Pacific Islander 463 5.3 177 3.6 281 7.5 5 6.0 

Hispanic/Latino 4,723 53.7 3,052 61.4 1,616 43.2 55 65.5 

Mixed Race 407 4.6 241 4.8 163 4.4 3 3.6 

Other 227 2.6 96 1.9 128 3.4 3 3.6 

Missing 51 0.6 24 0.5 26 0.7 1 1.2 
Recreational Water Contact and Illness in Mission Bay California 

18

Table 9. Household sociodemographic characteristics collected from study participants at all 

beaches from Mission Bay. 

Health Outcomes for Swimmers versus Non-swimmers 

Only two of the 14 health outcomes evaluated had an odds ratio that was consistently 

significantly elevated across all water exposures after adjustment for covariates (Table 10). The 

two outcomes for which there was increased risk were skin rash and diarrhea. Complete results 

for all health outcomes and all definitions of water exposure can be found in Appendix 2. 

While the risk of diarrhea was significantly increased among swimmers compared to nonswimmers, the risk was greatest in a narrow age band (Table 11). Five- to 12-year-old children 

had at least double the odds of this health outcome after any water contact compared to nonswimmers of the same age. The elevated odds ratio in this age group was seen across multiple 

definitions of water exposure ranging from “any water contact” to “swallowed water.” 

 

Surveyed Participants 

Characteristic N = 3,501 Households) 

n % 

Household size (# of persons) 

1 1,269 36.2 

2 649 18.5 

3 532 15.2 

4 511 14.6 

5 290 8.3 

6 140 4.0 

7 68 1.9 

>8 42 1.2 

Missing 0 0.0 

Country of Residence (HH) 

United States 3,170 90.5 

Mexico 66 1.9 

Canada 2 0.1 

Missing 263 7.5 

Average Annual Income (HH) 

< 10,000 284 8.1 

10,001 to 20,000 639 18.3 

20,001 to 30,000 444 12.7 

30,001 to 40,000 360 10.3 

40,001 to 50,000 294 8.4 

50,001 to 60,000 231 6.6 

60,001 to 70,000 181 5.2 

70,001 to 80,000 210 6.0 

80,001 to 100,000 229 6.5 

>100,000 309 8.8 

Missing 321 9.2 
Recreational Water Contact and Illness in Mission Bay California 

19

The risk of diarrhea was greater in Caucasian swimmers than in Hispanic swimmers, particularly 

among those who reported swallowing water (Table 12). The risk of diarrhea was significantly 

elevated for all ages of Caucasians after swallowing water, but was highest in Caucasian 

swimmers aged 5 to 12 years old. Although the risk of diarrhea was not statistically significantly 

elevated in Hispanic swimmers, the greatest odds ratios were observed in the 5- to 12-year-old 

age group. In contrast to the ethnic differences observed for diarrhea, the risk of skin rash was 

comparable between Caucasians and Hispanic swimmers despite increased water exposure. 

Odds ratios for skin rash were greatest in the 0- to 5-year-old age group compared to other age 

groups. When comparing ethnicity, odds ratios for skin rash were always greatest in Hispanic 

swimmers compared to Caucasians of the same age group. 

Table 10. Adjusted odds ratios (swimmers vs. non-swimmers) for health outcomes using various 

definitions of water exposure. Bolded numbers indicate statistical significance. 

Adjusted OR (95% CI) 

Health Outcome Any Water Contact Water on Face Swallow Water 

Gastrointestinal 

Diarrhea 1.36 (1.04-1.78) 1.54 (1.16 – 2.06) 1.89 (1.34 – 2.66) 

HCGI-1 0.96 (0.68-1.37) 1.03 (0.71 – 1.50) 1.01 (0.62, 1.66) 

HCGI-2 0.93 (0.49-1.75) 1.10 (0.57 – 2.13) 1.12 (0.51, 2.45) 

Nausea 0.88 (0.64-1.23) 1.11 (0.77, 1.61) 1.41 (0.91, 2.17) 

Cramps 1.07 (0.81-1.42) 1.14 (0.86, 1.51) 1.53 (1.08, 2.15) 

Vomiting 0.85 (0.58-1.26) 0.92 (0.61, 1.37) 0.86 (0.49, 1.52) 

Skin Rash 2.25 (1.60-3.16) 2.39 (1.72 – 3.31) 2.11 (1.37 – 3.24) 

Eye Irritation 1.19 (0.93 – 1.52) 1.29 (0.99 – 1.68) 1.69 (1.23 – 2.30) 

Ear 

Earache 0.96 (0.65-1.44) 1.00 (0.64 – 1.56) 1.10 (0.63 – 1.93) 

Ear Discharge 0.40 (0.16-1.01) 0.47 (0.19 – 1.13) 0.82 (0.22 – 3.00) 

Fever 0.96 (0.70-1.32) 1.04 (0.74 – 1.47) 1.15 (0.76 – 1.75) 

Respiratory 

SRD 1.08 (0.80-1.45) 1.03 (0.75 – 1.43) 0.99 (0.62 – 1.57) 

Sore Throat 0.89 (0.69-1.16) 0.96 (0.71 – 1.32) 0.87 (0.56 – 1.34) 

Cough 0.74 (0.54-1.02) 0.77 (0.54 – 1.11) 0.82 (0.47 – 1.41) 
Recreational Water Contact and Illness in Mission Bay California 

20

Table 11. Health outcomes by age group and water exposure. 

 

 Any Water Exposure 

 Age Group (years) 

 0 - 5 >5 – 12 >12 - 30 >30 

Gastrointestinal 

 Diarrhea 0.75 (0.40 - 1.40) 2.80 (1.07 - 7.27) 1.71 (0.96 - 3.05) 1.28 (0.85 - 1.93) 

 HCGI-1 0.86 (0.45 - 1.59) 1.33 (0.56 - 3.14) 0.73 (0.36 - 1.44) 1.37 (0.60 - 3.15) 

 HCGI-2 0.74 (0.31 - 1.75) 2.26 (0.28 - 18.45) 0.64 (0.15 - 2.74) 2.10 (0.30 - 14.73) 

 Nausea 1.90 (0.62 - 5.83) 1.40 (0.52 - 3.79) 0.46 (0.26 - 0.83) 1.11 (0.63 - 1.95) 

 Cramps 1.20 (0.53 - 2.70) 1.61 (0.77 - 3.37) 0.57 (0.34 - 0.94) 1.51 (0.93 - 2.43) 

 Vomiting 0.58 (0.31 – 1.10) 1.59 (0.54 – 4.68) 0.68 (0.31 – 1.47) 1.45 (0.64 – 3.30) 

Skin Rash 5.86 (1.81 - 19.0) 3.26 (1.30 - 8.15) 1.60 (0.89 - 2.86) 1.84 (1.04 - 3.25) 

Eye Irritation 0.53 (0.27 – 1.04) 1.84 (0.94 – 3.61) 1.21 (0.81 – 1.82) 1.23 (0.80 – 1.88) 

Ear 

 Earache 0.86 (0.31 – 2.39) 1.14 (0.37 – 3.49) 0.62 (0.30 – 1.25) 1.47 (0.73 – 2.96) 

 Ear Discharge 0.12 (0.01 – 1.66) 0.22 (0.03 – 1.59) 0.58 (0.14 – 2.37) 0.63 (0.10 – 3.86) 

Fever 0.68 (0.39 – 1.16) 1.67 (0.67 – 4.15) 0.83 (0.44 – 1.56) 1.44 (0.73 – 2.84) 

Respiratory 

 SRD 0.63 (0.32 – 1.22) 1.23 (0.57 – 2.66) 1.01 (0.58 – 1.75) 1.43 (0.86 – 2.35) 

 Sore Throat 0.74 (0.33 – 1.69) 1.21 (0.57 – 2.57) 0.82 (0.51 – 1.30) 0.90 (0.61 – 1.35) 

 Cough 0.52 (0.27 - 1.02) 0.84 (0.38 - 1.87) 0.78 (0.41 - 1.49) 0.84 (0.49 - 1.45) 
Recreational Water Contact and Illness in Mission Bay California 

21

(Table 11 Continued). Health outcomes by age group and water exposure. 

 Water On Face 

 Age Group (years) 

 0 - 5 >5 - 12 >12 - 30 >30 

Gastrointestinal 

 Diarrhea 0.92 (0.49 – 1.74) 3.11 (1.19 – 8.15) 2.40 (1.31 – 4.38) 1.15 (0.69 – 1.90) 

 HCGI-1 1.07 (0.57 – 2.00) 1.24 (0.52 – 2.98) 0.84 (0.40 – 1.77) 0.93 (0.31 – 2.77) 

 HCGI-2 0.95 (0.40 – 2.28) 2.48 (0.30 – 20.33) 0.95 (0.21 - 4.27) 0.53 (0.03 – 8.01) 

 Nausea 1.97 (0.72 – 5.42) 1.35 (0.52 – 3.51) 0.59 (0.30 – 1.16) 1.31 (0.65 – 2.63) 

 Cramps 1.51 (0.67, 3.40) 1.84 (0.88 - 3.83) 0.61 (0.36 - 1.03) 1.23 (0.73 - 2.06) 

 Vomiting 0.75 (0.39 – 1.42) 1.64 (0.55 – 4.89) 0.84 (0.39 – 1.83) 0.97 (0.34 – 2.79) 

Skin Rash 6.96 (2.14 – 22.62) 3.67 (1.47 – 9.17) 1.49 (0.86 – 2.57) 2.19 (1.21 – 3.95) 

Eye Irritation 0.54 (0.27 – 1.08) 1.88 (0.96 – 3.70) 1.39 (0.90 – 2.16) 1.25 (0.75 – 2.08) 

Ear 

 Earache 0.57 (0.18 – 1.79) 1.15 (0.37 – 3.60) 0.68 (0.31 – 1.48) 2.16 (0.97 – 4.83) 

 Ear Discharge 0.20 (0.02 – 2.39) 0.33 (0.05 – 2.24) 0.46 (0.11 – 1.98) 0.97 (0.20 – 4.64) 

Fever 0.74 (0.40 – 1.35) 1.78 (0.70 – 4.51) 1.23 (0.62 – 2.46) 0.76 (0.28 – 2.09) 

Respiratory 

 SRD 0.57 (0.29 – 1.14) 1.29 (0.58 – 2.84) 0.99 (0.55 – 1.79) 1.39 (0.76 – 2.53) 

 Sore Throat 0.73 (0.29 – 1.80) 0.88 (0.39 – 1.98) 1.22 (0.71 – 2.11) 0.98 (0.58 – 1.64) 

 Cough 0.42 (0.20 – 0.89) 0.93 (0.41 – 2.10) 0.80 (0.39 – 1.68) 0.99 (0.51 – 1.90) 

 

 Swallow Water 

 Age Group (years) 

 0 - 5 >5 - 12 >12 - 30 >30 

Gastrointestinal 

 Diarrhea 0.97 (0.47 - 2.01) 5.30 (1.96 - 14.33) 1.76 (0.79 - 3.91) 1.78 (0.86 - 3.66) 

 HCGI-1 0.61 (0.25 - 1.49) 1.72 (0.65 - 4.59) 1.34 (0.49 - 3.67) 0.70 (0.08 - 6.29) 

 HCGI-2 0.74 (0.23 – 2.36) 2.83 (0.32 – 24.83) 0.92 (0.13 – 6.46) 3.15 (0.18 – 54.04) 

 Nausea 2.27 (0.76 – 6.81) 2.29 (0.84 – 6.23) 0.56 (0.21 – 1.46) 2.08 (0.81 – 5.33) 

 Cramps 2.05 (0.88 – 4.78) 2.51 (1.18 – 5.33) 0.52 (0.23 – 1.18) 1.83 (0.85 – 3.92) 

 Vomiting 0.41 (0.14- 1.18) 2.15 (0.57 – 8.13) 1.27 (0.43 – 3.77) 1.13 (0.12 – 10.12) 

Skin Rash 10.42 (2.34 - 46.40) 4.10 (1.39 - 12.09) 1.15 (0.46 - 2.86) 1.32 (0.39 - 4.46) 

Eye Irritation 0.89 (0.41 – 1.92) 2.87 (1.44 – 5.71) 1.48 (0.82 – 2.67) 1.53 (0.72 – 3.25) 

Ear 

 Earache 0.25 (0.03 – 2.18) 2.09 (0.65 – 6.78) 0.78 (0.26 – 2.28) 0.89 (0.18 – 4.30) 

 Ear Discharge tf tf tf tf 

Fever 0.73 (0.36 – 1.45) 2.36 (0.88 – 6.28) 1.51 (0.64 – 3.55) 1.04 (0.22 – 4.91) 

Respiratory 

 SRD 0.62 (0.24 – 1.57) 1.18 (0.46 – 3.03) 1.03 (0.41 – 2.55) 0.71 (0.15 – 3.25) 

 Sore Throat 0.81 (0.26 – 2.50) 1.03 (0.42 – 2.52) 0.90 (0.38 – 2.10) 0.69 (0.25 – 1.86) 

 Cough 0.44 (0.15 - 1.32) 1.34 (0.48 - 3.70) 1.50 (0.53 - 4.27) tf 
Recreational Water Contact and Illnes

22

Table 12. Adjusted odds ratios (swimmers vs. non-swimmers) for diarrhea and skin rash using various definitions stratified by racial category and age group. 

Any Water Exposure Water on Face Swal

 Caucasian Hispanic Caucasian Hispanic Caucasian 

Diarrhea 

All Ages 2.16 (1.49 – 33.13) 0.98 (0.64 – 1.52) 2.38 (1.46 – 3.89) 1.16 (0.77 – 1.74) 3.92 (2.34 – 6.56) 0 – 5 1.73 (0.56 – 5.36) 0.68 (0.26 – 1.76) 2.01 (0.56 – 7.27) 1.06 (0.42 – 2.68) 5.47 (1.38 – 21.62) >5 – 12 4.90 (0.64 – 37.32) 2.70 (0.61 – 12.06) 5.84 (0.70 – 48.51) 2.09 (0.60 – 7.27) 8.53 (1.06 – 68.47) >12 – 30 2.33 (0.98 – 5.55) 1.20 (0.50 – 2.86) 3.17 (1.09 – 9.24) 1.87 (0.79 – 4.45) 3.66 (1.08 – 12.44) >30 1.96 (1.19 – 3.23) 0.69 (0.33 – 1.44) 1.79 (0.85 – 3.76) 0.62 (0.28 – 1.38) 3.32 (1.22 – 9.03) 

Skin Rash 

All Ages 2.44 (1.81 – 3.27) 2.09 (1.42 – 3.08) 2.39 (1.72 – 3.31) 2.19 (1.41 – 3.39) 2.11 (1.37 – 3.24) 0 – 5 5.86 (1.81 – 19.00) 12.05 (1.64 – 88.84) 6.96 (2.14 – 22.62) 12.01 (1.59 – 90.47) 10.42 (2.34 – 46.40>5 - 12 3.26 (1.3 – 8.15) 2.69 (0.96 – 7.53) 3.67 (1.47 – 9.17) 3.24 (1.14 – 9.21) 4.10 (1.39 – 12.09) >12 - 30 1.60 (0.89 – 2.86) 1.39 (0.67 – 2.86) 1.49 (0.86 – 2.57) 1.52 (0.69 – 3.35) 1.15 (0.46 – 2.86) >30 1.84 (1.04 – 3.25) 1.09 (0.53 – 2.22) 2.19 (1.21 – 3.95) 1.51 (0.67 – 3.40) 1.32 (0.39 – 4.46) 
Recreational Water Contact and Illness in Mission Bay California 

23

The calculated attributable risks (Table 13) for diarrhea estimated an excess of 11.1 cases 

of diarrhea per 1,000 swimmers who had any contact with the water in Mission Bay 

during the study period. This risk increased as the intensity of water exposure increased, 

with 16.1 per 1,000 among those who reported facial contact with water and 27.2 cases 

per 1,000 swimmers who reported swallowing water. Children aged 5 to 12 years old 

had the greatest attributable risk for diarrhea following swimming. For example, this age 

group showed an estimated excess of 27.4 cases per 1,000 among children with any water 

contact, an excess of 31.9 cases per 1,000 among those with facial contact with the water, 

and an excess of 59 cases per 1,000 among those who swallowed water. Excess cases of 

skin rash were highest in the 0- to 5–year-old age group, ranging from an excess of 46.8 

per 1,000 with any water contact to 56.2 per 1,000 swimmers in this age group who 

swallowed water. 

Table 13. Frequency (percent) reporting illness and calculated attributable risk (per 1,000 

swimmers). 

 

Diarrhea 

 Percent ill - Adjusted 

 

Adjusted Attributable Risk 

(95% CI) (expressed as 

excess cases per 1,000 

swimmers) Non-swimmers Swimmers 

Any Water Contact 

All Ages 11.1 (0.0 - 22.1) 3.20 4.31 

0 - 5 -14.1 (-47.7 – 18.5) 6.01 4.60 

>5 - 12 27.4 (-8.9 - 63.7) 1.59 4.33 

>12 - 30 14.3 (-7.0 - 35.6) 2.09 3.51 

>30 10.0 (-8.6 - 28.6) 3.74 4.75 

 

Water on Face 

All Ages 16.1 (3.6 - 38.6) 3.10 4.71 

0 - 5 -4.2 (-36.7 – 28.4) 5.27 5.69 

>5 - 12 31.9 (2.1 – 61.7) 1.58 4.78 

>12 - 30 26.4 (-2.6 – 5.54) 1.98 4.62 

>30 5.2 (-15.1 - 25.6) 3.73 4.25 

 

Swallow Water 

All Ages 27.2 (8.9 – 45.6) 3.25 5.97 

0 - 5 -1.6 (-42.5 - 39.4) 6.09 5.93 

>5 - 12 59.0 (15.0 – 103.0) 1.48 7.38 

>12 - 30 18.5 (-13.6 - 50.6) 2.55 4.40 

>30 26.4 (-15.7 - 68.4) 3.63 6.28 
Recreational Water Contact and Illness in Mission Bay California 

24

(Table 13 Continued). Frequency (percent) reporting illness and calculated attributable 

risk (per 1,000 swimmers). 

 

Skin Rash 

 Percent ill - Adjusted 

 

Adjusted Attributable risk 

(95% CI) (expressed as 

excess cases per 1,000 

swimmers) Non-swimmers Swimmers 

Any Water Contact 

All Ages 19.0 (10.9 – 27.1) 1.58 3.48 

0 – 5 46.8 (26.2 – 67.4) 1.02 5.70 

>5 - 12 34.1 (15.8 – 52.3) 1.59 4.99 

>12 - 30 10.9 (-2.3 – 24.1) 1.88 2.97 

>30 10.6 (0.2 - 21.0) 1.27 2.31 

 

Water on Face 

All Ages 22.6 (13.6 – 31.6) 1.69 3.95 

0 - 5 52.1 (31.3 - 72.9) 0.93 6.14 

>5 - 12 38.7 (20.4 - 57.0) 1.53 5.41 

>12 - 30 10.8 (-4.3 - 25.9) 2.28 3.36 

>30 15.0 (2.1 - 27.8) 1.30 2.80 

 

Swallow Water 

All Ages 18.0 (3.7 – 32.3) 1.69 3.49 

0 - 5 56.2 (-5.5 - 118.0) 0.64 6.3 

>5 - 12 39.4 (5.0 - 73.7) 1.34 5.28 

>12 - 30 3.1 (18.1 – 24.2) 2.08 2.39 

>30 4.1 (-16.8 – 25.1) 1.34 1.75 

 
Recreational Water Contact and Illness in Mission Bay California 

25

Relationship between Health Outcomes and Water Quality 

No correlation was observed between increased risk of illness and increased levels of 

traditional water quality indicators including enterococcus, fecal coliform, or total 

coliform. Using diarrhea as an example, odds ratios were not statistically significantly 

elevated due to increases in enterococcus (Table 14). The lack of relationship resulted 

despite numerous approaches to water quality exposure (i.e.. combining or separating 

sites at a beach) or calculation of indicator metrics (i.e., daily geomean, daily maxima, or 

various cutpoints). Of particular note, the state water quality thresholds did not correlate 

with an increased risk of illness (Table 15). 

Additionally, no correlation was found between increased risk of illness and levels of 

Bacteroides, enterococcus using rapid methods (QPCR), human pathogenic virus 

(adenovirus and Norwalk-like virus), or somatic phage. The relationship with viruses 

was difficult to evaluate, though, because no human pathogenic virus was found and 

adenovirus was only found in one sample. While low virus counts do not allow 

evaluation of a potential relationship with the two symptoms that were elevated in 

swimmers (skin rash and diarrhea), the low counts were consistent with the absence of 

increased health risk for the other health outcomes evaluated. 

Significant associations between the levels of male-specific coliphage and HCGI-1, 

HCGI-2, nausea, cough, and fever were observed (Table 16). However, a low number of 

participants were exposed to the water at times when male-specific coliphage was 

detected (Table 17). Therefore, the relationships between male-specific coliphage and 

various outcomes should be interpreted cautiously. Results for all health outcomes for 

various indicator and water exposure levels are presented in Appendix 3. 

Table 14. Adjusted odds ratio for diarrhea after two weeks for various water quality 

exposure metrics for enterococcus. The unit change in exposure in these models was set 

to represent a change of (ln 30). There were no statistically significant results. 

Any Water Contact Water on Face Swallow Water 

Ln Daily Geomean @ Station Level 0.57 (0.30 – 1.07) 0.66 (0.32 – 1.34) 0.21 (0.05 – 0.85) 

Ln Daily Geomean @ Beach Level 0.77 (0.33 – 1.80) 0.62 (0.24 – 1.60) 0.31 (0.06 – 1.59) 

Ln Daily Max @ Station Level 0.67 (0.45 - 1.02) 0.77 (0.47 – 1.24) NA 

Ln Daily Max @ Beach Level 0.99 (0.71 – 1.38) 0.93 (0.64 – 1.34) NA 
Recreational Water Contact and Illness in Mission Bay California 

26

Table 15. Adjusted odds ratios for health outcomes using two dichotomous measures of 

exposure to enterococcus. 

Adjusted OR (95% CI) Health Outcome 

> 35 vs. < 35 > 104 vs. < 104 

Gastrointestinal 

 Diarrhea 1.01 (0.73-1.39) 1.22 (0.85-1.76) 

 HCGI-1 0.74 (0.51-1.06) 1.13 (0.73-1.75) 

 HCGI-2 0.69 (0.38-1.25) 0.80 (0.37-1.73) 

 Nausea 0.78 (0.51-1.20) 1.12 (0.65-1.92) 

 Cramps 0.91(0.66-1.24) 1.36 (0.95-1.95) 

 Vomiting 0.67 (0.43-1.03) 1.13 (0.67-1.92) 

 

Skin Rash 0.83 (0.61-1.15) 1.00 (0.67 – 1.49) 

 

Eye Irritation 0.97 (0.72-1.32) 0.77 (0.53-1.11) 

 

Ear 

 Earache 1.08 (0.68-1.70) 1.18 (0.70-2.00) 

 Ear Discharge 1.15 (0.30-4.36) 0.94 (0.19-4.62) 

 

Fever 0.92 (0.65-1.31) 0.89 (0.58-1.37) 

 

Respiratory 

 SRD 0.96 (0.67-1.37) 1.13 (0.73-1.73) 

 Sore Throat 1.10 (0.80-1.50) 1.15 (0.77-1.72) 

 Cough 0.65 (0.40-1.05) 0.51 (0.25-1.03) 
Recreational Water Contact and Illness in Mission Bay California 

27

Table 16. Adjusted odds ratios for various health outcomes after two weeks for water 

exposures (per unit increase) to male-specific coliphage. Statistically significant results 

are shown in bold face type. 

Any Water Contact 

Health Outcome Adjusted OR (95% CI) 

Gastrointestinal 

HCGI-1 1.26 (1.06, 1.48) 

HCGI-2 1.43 (1.13, 1.82) 

Nausea 1.34 (1.16, 1.55) 

Diarrhea 1.14 (0.97, 1.35) 

Cramps 1.04 (0.83, 1.32) 

Vomiting 1.21 (0.96, 1.53) 

Skin Rash 1.00 (0.77, 1.31) 

Eye Irritation 1.14 (0.95, 1.36) 

Fever 1.25 (1.09, 1.44) 

Ear 

Earache Too few 

Ear Discharge Too few 

Respiratory 

SRD 1.05 (0.85, 1.31) 

Cough 1.22 (1.02, 1.48) 

Sore Throat 1.04 (0.83, 1.30) 

Table 17. Association of male-specific coliphage (defined as >0.10 cfu) with diarrhea. 

Diarrhea Reported No Diarrhea Reported Total 

Male-specific Phage 

Present (>0.10 cfu) 

8 153 161 

Male-specific Phage 

Absent 

195 3,878 4,073 

Total 203 4,031 4,234 

Time in the water 

We also examined whether swimmers with prolonged water exposure (>1 hour) to 

Mission Bay had an elevated risk of illness compared to non-swimmers and found an OR 

of 1.44, 95% CI 1.08-1.92. This result is similar to that found in Table 10 for swimmers 

with any water contact compared to non-swimmers (1.36, 95% CI 1.04-1.78), suggesting 

a small but insignificant increase in the risk from prolonged exposure. 

Among swimmers with greater than 1 hour of water exposure, the odds ratio for a 30-unit 

(3.4 log) increase in enterococcus was 0.74 (0.23-2.36). This result is similar to that seen 

for the risk of diarrhea among swimmers (defined as “any water contact”) exposed to 

enterococcus (0.57, 95% CI 0.30-1.07) for exposure measured as the ln of the daily 

geomean at the station level (Table 14). 
Recreational Water Contact and Illness in Mission Bay California 

28

DISCUSSION 

Unlike most previous marine recreational epidemiology studies, this study found no 

relationship between illness rates and fecal indicator bacteria densities despite 

investigating numerous exposure measures. Wade et al. (2003) systematically reviewed 

27 highly relevant marine recreational water epidemiology studies and found an increase 

in relative risk with increasing fecal indicator concentrations, particularly for 

enterococcus. For example, the observed increase in risk of swimming-associated 

illnesses from both Cabelli et al. (1982) and Haile et al. (1999) was highly correlated 

with increasing enterococcus concentrations. In virtually all of the studies summarized 

by Wade et al. (2003), however, water quality was impacted by known sources of human 

fecal contamination. The relationship with enterococcus, or any other fecal indicator 

bacteria, did not exist in Mission Bay, and one explanation for this difference may be the 

predominance of non-human fecal sources in Mission Bay. While animal sources can 

also harbor disease-causing agents, they are less likely to serve as vectors for human 

disease (NRC 2004). 

The use of bacterial indicators as a predictor of swimming-associated illnesses is based 

on the presumption that they have survival properties similar to the pathogens they are 

intended to mirror. This presumption is less likely to remain true when circulation is 

restricted and residence times increase, which can be days to weeks in Mission Bay 

(Largier et al. 2003). Increased survival, and perhaps even regrowth of fecal indicator 

bacteria, has been suggested in sediments and wrack lining beaches including Mission 

Bay (Weiskel et al. 1996, City of San Diego/MEC Weston 2004). Regardless, the lack of 

relationship of non-human sources of fecal indicator bacteria to health risk suggests that 

the 28 water contact advisories posted at beaches in Mission Bay during the course of this 

study were misleading from a public health perspective, but were required by law. 

It is arguable whether the viral measures in our study were better indicators of health risk 

and could be used in place of bacterial indicators for health risk assessments in Mission 

Bay. We found that increasing density of male-specific phage was correlated with 

increased incidence of several health outcomes, including HCGI-1, HCGI-2, nausea, 

cough, and fever. This is consistent with the success of this measure in freshwater 

application (Lee et al. 1997). However, we interpret these associations cautiously 

because male-specific coliphage were not detected often and so few subjects were 

exposed to the water at those times. 

The human-specific viruses we measured in Mission Bay were rarely detected, which 

corresponds well with our low rates of swimming-associated illnesses. We did not 

encounter high virus counts that would have allowed us to assess their effectiveness as 

predictors in the positive direction. Moreover, even interpretation of viruses as negative 

predictors is compromised by technology limitations. We used the most advanced 

techniques available, but quantifying virus particles in seawater is difficult because DNA 

and RNA are lost due to complexation and interferences when concentrating and 

extracting nucleic acid material. Thus, we cannot be certain that the low levels we 
Recreational Water Contact and Illness in Mission Bay California 

29

observed were due to their absence from the system or from difficulties in recovering 

viruses that were present. However, our results do suggest that these non-bacterial 

measures have the potential to be more effective than traditional bacterial indicators as 

predictors of illness when non-human sources are dominant. 

While we found that traditional fecal indicators were ineffective predictors of health 

effects in this study, it is difficult to extrapolate this finding beyond Mission Bay. 

Mission Bay is unusual in that it has been subjected to extensive cleanup activities and 

source tracking studies have identified that human fecal sources are now only a minor 

contributor to the overall bacterial load (City of SD/MEC Weston 2004). Our study, 

though, does suggest the need for further evaluation of traditional fecal indicator bacteria 

in circumstances where non-point, non-human contributions are the dominant fecal 

source. 

It is important not to extrapolate our results beyond our study conditions. We would 

expect to see an increase in health risks, and likely an association with water quality 

indicators, if large sources of untreated human fecal material entered the Bay. Such a 

situation could occur when sewage overflows spill into the Bay. 

Finally, we examined swimming-related illnesses during dry weather. No 

epidemiological data at any beach currently exists for health risks associated with 

swimming at these beaches following wet-weather events. 
Recreational Water Contact and Illness in Mission Bay California 

30

STUDY CONCLUSIONS

The Mission Bay Epidemiology Study was successfully implemented, collecting 

sufficient water quality data and recruiting sufficient numbers of participants. Based on 

the resulting data, the answers to our study questions can be summarized as follows: 

• Water contact moderately increased the risk of illness in the two weeks following 

exposure to water in Mission Bay during the summer of 2003. 

Two of the 14 health outcomes evaluated had an odds ratio that was significantly 

elevated after adjustment for covariates. The probability of skin rash and diarrhea 

was consistently significantly elevated in swimmers compared to non-swimmers in 

Mission Bay during the summer of 2003. The probability of more severe health 

outcomes such as highly credible gastrointestinal illnesses (HCGI-1 or HCGI-2) and 

significant respiratory disease (SRD) were not significantly elevated in swimmers 

compared to non-swimmers. 

• Among those individuals with water contact, there were no associations between 

illness and measured levels of traditional indicators of water quality. 

No correlation between increased risk of illness and increased levels of traditional 

water quality indicators (including enterococcus, fecal coliform, or total coliform) 

was found. This resulted despite numerous approaches to water quality exposure 

(combining or separating sites at a beach) or calculation of indicator metrics (daily 

geomean or maxima, various cutpoints, etc.). Of particular note in this study, the 

state water quality thresholds were not predictive of swimming-related illnesses. 

• Among those individuals with water contact, there were no associations between 

illness and measured levels of any non-traditional indicators of water quality except 

for male-specific coliphage. 

No correlation between increased risk of illness and increased levels of Bacteroides, 

enterococcus using rapid methods (QPCR), human pathogenic virus (adenovirus and 

Norwalk-like virus), or somatic phage was found. Since traditional enterococcus 

methods were unsuccessful at predicting swimming-associated illnesses, it is not 

surprising that the newer, more rapid methods were equally unsuccessful. Virtually 

no human pathogenic virus was found; adenovirus was only quantified in one sample. 

A significant association between the levels of male-specific coliphage and HCGI-1, 

HCGI-2, nausea, cough, and fever was observed. We interpret these associations 

cautiously, however, because so few subjects overall were exposed to the water at 

times when male-specific coliphage was detected. 
Recreational Water Contact and Illness in Mission Bay California 

31

The findings from Mission Bay are unique in this field, largely because Mission Bay may 

be a unique circumstance. Certainly, many other enclosed marine beaches, particularly in 

California, suffer from impaired water quality due to non-point sources of bacteria and 

poor circulation. However, it is premature at this time to extrapolate the findings from 

the current study to other enclosed marine beaches, especially if significant source 

identification work has not been accomplished. Moreover, the epidemiological findings 

from Mission Bay were collected from periods of dry weather and no known sewage 

spills. We would expect to see an increase in health risks, and likely an association with 

water quality indicators, if large sources of untreated human fecal material entered the 

Bay. No epidemiological data currently exists for health risks associated with swimming 

at these beaches following wet-weather events. 
Recreational Water Contact and Illness in Mission Bay California 

32

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Haugland, R.A. In press. Rapid Measurement of Bacterial Fecal Indicators In Surface 

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Recreational Water Contact and Illness in Mission Bay California 

35

APPENDICES 

Appendix 1: Mission Bay Human Subjects Protocol, Study Instruments, and 

Consent Form 

Appendix 2: Health Outcomes vs. Water Exposure Analyses 

Appendix 3: Health Outcomes vs. Water Quality Indicator & Water Exposures 

Analyses 

Appendix 4: Sociodemographic Characteristics of Study Population 

Appendix 5: Participant Responses to Questions Regarding Exposures and Illness 

Prior to Beach Visit 

Appendix 6: Participant Responses to Questions Regarding Exposures During 

Beach Visit 

Appendix 7: Participant Responses to Follow-up Questions Regarding Exposures 

Following Beach Visit