Elevated bathing-associated disease risks despite certified water quality: a cohort study

Bacteriological water quality criteria have been recommended to ensure bathers' health. However, this risk-assessment approach is based mainly on routine measurements of fecal pollution indicator bacteria in seawater, and may not be adequate to protect bathers effectively. The aim of this study was to assess the risks of symptoms related to infectious diseases among bathers after exposure to seawater which was of excellent quality according to EU guidelines. This study is a cohort study recruiting bathers and non-bathers. Water samples were collected for estimating bacterial indicators. Univariable and multivariable analysis was performed to compare the risks of developing symptoms/diseases between bathers and non-bathers. A total of 3805 bathers and 572 non-bathers were included in the study. Water analysis results demonstrated excellent quality of bathing water. Significantly increased risks of symptoms related to gastrointestinal infections (OR = 3.60, 95% CI 1.28-10.13), respiratory infections (OR = 1.92, 95% CI 1.00-3.67), eye infections (OR = 2.43, 95% CI 1.27-4.63) and ear infections (OR = 17.21, 95% CI 2.42-122.34) were observed among bathers compared with non-bathers. Increased rates of medical consultation and medication use were also observed among bathers. There was evidence that bathers experienced increased morbidity compared with non-bathers though the bathing waters met bacteriological water quality criteria. These results suggest that risk assessments of recreational seawaters should not only focus on bacteriological water quality criteria.     

Health risk of bathing in Southern California coastal waters

Urbanized areas often discharge large volumes of contaminated waste into coastal waters, which may pose a health risk to bathers at nearby beach areas. In this investigation the authors estimated the number of gastrointestinal and respiratory illness episodes associated with the microbial contamination of coastal waters among bathers at Southern California beaches from 2000 through 2004. Bathers at the 67 beaches along the 350-km coastline of Southern California were the study population in this investigation. The authors' estimates were derived from a simulation model, which utilized water quality, beach attendance, and bathing-rate data, along with the three concentration-response relationships that underlie US Environmental Protection Agency, World Health Organization, and European Union marine water-quality guidelines. Given the absence of a general surveillance program to monitor these illnesses in Southern California, simulation modeling provides an established method to derive health risk estimates, despite additional analytic uncertainty that may accompany modeling-based analyses. An estimated 689,000 to 4,003,000 gastrointestinal illness episodes and 693,000 respiratory illness episodes occurred each year. The majority of illnesses (57% to 80%) occurred during the summer season as a result of large seasonal increases in beach attendance and bathing rates. As 71% of gastroenteritis episodes were estimated to occur when the water quality was considered safe for bathing, California's marine water-contact standards may be inadequate to protect the health of bathers.     

Recreation in coastal waters: health risks associated with bathing in sea water

STUDY OBJECTIVE: To find out whether bathing in sewage polluted waters implies a danger to bathers' health and to determine the best microbiological indicator to predict the relation between bathing and the appearance of some symptoms. DESIGN: Cohort study. SETTING: City of Santander (north of Spain). PARTICIPANTS: From the people going to four Santander beaches in the period from 1 July to 16 September 1998, a cohort of 2774 persons was recruited who agreed to participate in this study. Of those, 1858 successfully completed a follow up interview conducted in seven days. Respiratory, gastrointestinal, eye, and ear symptoms, and fever occurring during the seven day follow up were recorded. MAIN RESULTS: A total of 136 participants (7.5%) reported symptoms. Visitors reported experiencing symptoms with more frequency than residents. Incidence rates of gastrointestinal, cutaneous and high respiratory tract symptoms were higher in bathers, but the differences were not significant. Total symptoms were related with the amount of total coliforms, faecal coliforms, and faecal streptococci in the water. Gastrointestinal and skin symptoms kept a positive trend with the degree of water pollution by total coliforms in both crude and adjusted analyses. An increased risk was observed in 2500-9999 total coliforms per 100 ml, a figure over the proposed standard, although below the European Union mandatory limit. CONCLUSIONS: The results of this study suggest that total coliforms are the best predictors of the symptoms.     

Risks Associated with the Microbiological Quality of Bodies of Fresh and Marine Water Used for Recreational Purposes: Summary Estimates Based on Published Epidemiological Studies

The current European standards for microbiological quality of bathing water (i.e., all running or still fresh waters or parts thereof and/or sea water [with the exception of water intended for therapeutic purposes and water used in swimming pools]) were issued in 1976 and are currently undergoing revision. In this article, the authors propose parameters for select microorganism indicators to assist in the establishment of public-health-based objectives for fresh and marine water quality. A type-II meta-analysis of the results of 18 published epidemiological studies was implemented in an attempt to characterize the relationship(s) between concentrations of bacterial indicators and rates of acute gastrointestinal diseases among bathers who had used fresh or marine water for recreational purposes. The authors fit multiple linear-regression models, which allowed for random effects across studies, to derive dose-response curves. Several confounders and effect modifiers were controlled for in the analyses. Risks were then estimated for a hypothetical individual who would bathe 20 times/yr in water that contained a given concentration of microorganisms. For fresh-water-associated highly credible gastrointestinal illnesses, a level of 10 fecal coliforms/100 ml water yielded an attributable risk of 0.2 cases/1,000 person-years; a risk of 2 cases/1,000 person-years was found for fecal streptococci. The corresponding yearly attributable risks were 1 and 13 cases/1,000 person-years, respectively, for 100 bacteria/100 ml fresh water. Risks associated with fecal coliforms were found to be lower in marine water than in fresh water. Irrespective of the type of water examined, total coliforms were related only weakly with acute digestive morbidity. Developers of future bathing-water standards should state the level of risk deemed acceptable for public health. The authors of this study maintain that levels of fecal coliforms and fecal streptococci should be used as criteria for infectious risk management associated with bodies of marine and fresh water used for recreational purposes.     

Risks associated with the microbiological quality of bodies of fresh and marine water used for recreational purposes: summary estimates based on published epidemiological studies

The current European standards for microbiological quality of bathing water (i.e., all running or still fresh waters or parts thereof and/or sea water [with the exception of water intended for therapeutic purposes and water used in swimming pools]) were issued in 1976 and are currently undergoing revision. In this article, the authors propose parameters for select microorganism indicators to assist in the establishment of public-health-based objectives for fresh and marine water quality. A type-II meta-analysis of the results of 18 published epidemiological studies was implemented in an attempt to characterize the relationship(s) between concentrations of bacterial indicators and rates of acute gastrointestinal diseases among bathers who had used fresh or marine water for recreational purposes. The authors fit multiple linear-regression models, which allowed for random effects across studies, to derive dose-response curves. Several confounders and effect modifiers were controlled for in the analyses. Risks were then estimated for a hypothetical individual who would bathe 20 times/yr in water that contained a given concentration of microorganisms. For fresh-water-associated highly credible gastrointestinal illnesses, a level of 10 fecal coliforms/100 ml water yielded an attributable risk of 0.2 cases/1,000 person-years; a risk of 2 cases/1,000 person-years was found for fecal streptococci. The corresponding yearly attributable risks were 1 and 13 cases/1,000 person-years, respectively, for 100 bacteria/100 ml fresh water. Risks associated with fecal coliforms were found to be lower in marine water than in fresh water. Irrespective of the type of water examined, total coliforms were related only weakly with acute digestive morbidity. Developers of future bathing-water standards should state the level of risk deemed acceptable for public health. The authors of this study maintain that levels of fecal coliforms and fecal streptococci should be used as criteria for infectious risk management associated with bodies of marine and fresh water used for recreational purposes.     

A survey of diving behaviour and accidental water ingestion among Dutch occupational and sport divers to assess the risk of infection with waterborne pathogenic microorganisms

Divers may run a higher risk of infection with waterborne pathogens than bathers because of more frequent and intense contact with water that may not comply with microbiologic water quality standards for bathing water. In this study we aimed to estimate the volume of water swallowed during diving as a key factor for infection risk assessment associated with diving. Using questionnaires, occupational and sport divers in the Netherlands were asked about number of dives, volume of swallowed water, and health complaints (nausea, vomiting, diarrhea, and ear, skin, eye, and respiratory complaints). Occupational divers, on average, swallowed 9.8 mL marine water and 5.7 mL fresh surface water per dive. Sport divers swallowed, on average, 9.0 mL marine water; 13 mL fresh recreational water; 3.2 mL river, canal, or city canal water; and 20 mL water in circulation pools. Divers swallowed less water when wearing a full face mask instead of an ordinary diving mask and even less when wearing a diving helmet. A full face mask or a diving helmet is recommended when diving in fecally contaminated water. From the volumes of swallowed water and concentrations of pathogens in fecally contaminated water, we estimated the infection risks per dive and per year to be as high as a few to up to tens of percents. This may explain why only 20% of the divers reported having none of the inquired health complaints within a period of 1 year. It is highly recommended that divers be informed about fecal contamination of the diving water.     

Bathers as a possible source of contamination for swimming‐associated illness at marine bathing beaches

The results of a prospective, follow‐up epidemiological study conducted at three Israeli coastal beaches in 1983 showed that enteric, respiratory and ear symptomatology were higher among swimmers than nonswimmers, especially for young children. The enterococcus levels and the swimming‐associated rates for enteric and respiratory symptoms at one of the beaches (Gordon) were at least twice those at another beach (Rishon Lezion). The higher swimming‐associated symptom rates at Gordon Beach, however, were largely attributable to individuals who swam on Saturdays, which are non‐working days in Israel, as opposed to Fridays and Sundays. The absence of extrinsic sources of pollution, the restricted water exchange due to horizontal surf‐breakers, the greater bather density and higher indicator levels (including those of Staphylococcus aureus) on Saturdays and the better correlation of S. aureus than enterococcus (or Escherichia cofi) levels to swimming‐associated enteric and respiratory symptoms, suggests that contamination from the bathers themselves is the source of the indicators and swimming‐associated illness at Gordon Beach.     

Web-based investigation of water associated illness in marine bathers

Internet-based methods of disease investigation have proven useful for drinking water and foodborne illness but have not been applied to recreational water illness (RWI) in marine bathers. We analyzed responses to a web-based survey posted by Surfrider Foundation over the period 1996-2005. Subjects (n=1895) were recruited by self-selection via website visitation. Complaints were screened to meet inclusion criteria (n=1190). Demographic characteristics of respondents were assessed as well as the types and severity of their symptoms. Geographic information systems (GIS) were used to examine spatial patterns in survey data. Illness complaints were commonly received in summer from heavily used California beaches. A strong correlation was observed between water quality impairment and the number of illness complaints in coastal counties (r=0.96, p<0.01). Respondents most commonly complained of gastrointestinal symptoms, infections of the sinuses and other upper respiratory ailments. Certain severe symptoms, such as high fevers, severe vomiting and/or diarrhea, seizures, swollen glands, and infections that did not heal properly were also reported. Approximately one-third of respondents sought the care of a physician for their symptoms; however, less than 1% reported being hospitalized. Our findings concerning the nature of the described symptoms as well as the observed seasonal and spatial patterns in the data are consistent with previously published findings of RWI in ocean bathers exposed to sewage and urban runoff. This method of rapid RWI data collection over the web could easily be adopted by health agencies for coordinated disease surveillance.     

Evaluation of recreational health risk in coastal waters based on enterococcus densities and bathing patterns

We constructed a simulation model to compute the incidences of highly credible gastrointestinal illness (HCGI) in recreational bathers at two intermittently contaminated beaches of Orange County, California. Assumptions regarding spatial and temporal bathing patterns were used to determine exposure levels over a 31-month study period. Illness rates were calculated by applying previously reported relationships between enterococcus density and HCGI risk to the exposure data. Peak enterococcus concentrations occurred in late winter and early spring, but model results showed that most HCGI cases occurred during summer, attributable to elevated number of exposures. Approximately 99% of the 95,010 illness cases occurred when beaches were open. Model runs were insensitive to 0-10% swimming activity assumed during beach closure days. Comparable illness rates resulted under clustered and uniform bather distribution scenarios. HCGI attack rates were within federal guidelines of tolerable risk when averaged over the study period. However, tolerable risk thresholds were exceeded for 27 total days and periods of at least 6 consecutive days. Illness estimates were sensitive to the functional form and magnitude of the enterococcus density-HCGI relationships. The results of this study contribute to an understanding of recreational health risk in coastal waters.     

Daily measures of microbes and human health at a non-point source marine beach

Studies evaluating the relationship between microbes and human health at non-point source beaches are necessary for establishing criteria which would protect public health while minimizing economic burdens. The objective of this study was to evaluate water quality and daily cumulative health effects (gastrointestinal, skin, and respiratory illnesses) for bathers at a non-point source subtropical marine recreational beach in order to better understand the inter-relationships between these factors and hence improve monitoring and pollution prevention techniques. Daily composite samples were collected, during the Oceans and Human Health Beach Exposure Assessment and Characterization Health Epidemiologic Study conducted in Miami (Florida, USA) at a non-point source beach, and analyzed for several pathogens, microbial source tracking markers, indicator microbes, and environmental parameters. Analysis demonstrated that rainfall and tide were more influential, when compared to other environmental factors and source tracking markers, in determining the presence of both indicator microbes and pathogens. Antecedent rainfall and F+ coliphage detection in water should be further assessed to confirm their possible association with skin and gastrointestinal (GI) illness outcomes, respectively. The results of this research illustrate the potential complexity of beach systems characterized by non-point sources, and how more novel and comprehensive approaches are needed to assess beach water quality for the purpose of protecting bather health.     

Real and irrelevant risks of infection by swimming in recreational bodies of water

Life-threatening infectious diseases associated with recreational water exposure are possible but occur very rarely. About eighty per cent of all infections due to bathing water produced gastroenteritis, the remaining were spontaneously healing infections of ear, nose and throat as well as eye and respiratory symptoms. They are caused by endogenic and exogenic agents. The risk, i.e. the mean frequency of such commonplace diseases associated with bathing or swimming is already doubled by endogenic infectious agents even without any etiological agents in the recreational water. The additional risk by exogenic infectious agents increases with the concentration of fecal markers. The prescribed limit E coli value of 200 CFU per 100 ml of the EU guidelines for bathing waters corresponds to a risk increased by the factor 7-8. The Bathing Water Committee of the German Federal Environmental Agency issued new recommendations prescribing severely lowered limit values. For example, the Committee called for 100 CFU of E. coli per 100 ml. However, there are economical and legal objections as well as doubts regarding the Committee's scientific competence. The lower limit values are associated with high expenses for communities and bathers without recognizable returns in terms of efficiency. Furthermore, they offend against the legal principle of equality because newly constructed pools are not different from bathing water regulated according to EU guidelines. Finally, the Bathing Water Committee holds scientifically incorrect views on infectious agents and on the risks in recreational waters.     

Usefulness of monitoring tropical streams for male-specific RNA coliphages

The objective of this study was to evaluate the usefulness of monitoring streams in Hawaii for FRNA coliphages as a reliable indicator of sewage contamination. This study was undertaken as a result of our previous findings that monitoring streams in Hawaii for traditional faecal indicator bacteria (faecal coliform, Escherichia coli, enterococci) was not useful in determining when streams are contaminated with sewage, because environmental (soil) sources rather than sewage accounted for the high concentrations of faecal bacteria in streams. Two perennial streams, sewage and soil samples were monitored for traditional faecal indicator bacteria (faecal coliform, E. coli, enterococci) and FRNA coliphages. The results showed that sewage treatment processes and disinfection drastically reduced the concentrations of traditional faecal indicator bacteria but FRNA coliphages were still present in significant concentrations in the treated sewage effluents. These results indicate that monitoring sewage effluents and environmental waters for only traditional faecal indicator bacteria may not be adequately protective of human health effects. Ambient concentrations of traditional faecal indicator bacteria in soil and streams of Hawaii were consistently high but consistently low for FRNA coliphages, indicating that monitoring streams of Hawaii for FRNA coliphages can be used to determine when streams are contaminated with sewage.     

Microbial quality of tilapia reared in fecal-contaminated ponds

The microbial quality of tilapia reared in four fecal-contaminated fishponds was investigated. One of the fishponds (TDP) received treated sewage with an average fecal coliform count of 4 x 10(3)cfu/100mL, and feed of fresh duckweed grown on treated sewage was used. The number of fecal coliform bacteria attached to duckweed biomass ranged between 4.1 x 10(2) and 1.6 x 10(4)cfu/g fresh weight. The second fishpond (TWP) received treated sewage, and the feed used was wheat bran. The third fishpond (FDP) received freshwater, and the feed used was the same duckweed. Pond 4 (SSP) received only settled sewage with an average fecal coliform count of 2.1 x 10(8)/100mL. The average counts in the fishponds were 2.2 x 10(3), 1.7 x 10(3), 1.7 x 10(2), and 9.4 x 10(3)cfu/100mL in TDP, TWP, FDP, and SSP, respectively. FDP had a significantly (P < 0.05) lower fecal coliform count than the treated sewage-fed ponds and SSP. The microbial quality of the tilapia indicated that all tissue samples except muscle tissues were contaminated with fecal coliform. Ranking of the fecal coliform contamination levels showed a decrease in the order intestine>gills>skin>liver. Poor water quality (ammonia and nitrite) in SSP resulted in statistically higher fecal coliform numbers in fish organs of about 1 log(10) than in treatments with good water quality. Pretreatment of sewage is therefore recommended.     

High sensitivity of children to swimming-associated gastrointestinal illness: results using a rapid assay of recreational water quality

BACKGROUND: Culture-based methods of monitoring fecal pollution in recreational waters require 24 to 48 hours to obtain results. This delay leads to potentially inaccurate management decisions regarding beach safety. We evaluated the quantitative polymerase chain reaction (QPCR) as a faster method to assess recreational water quality and predict swimming-associated illnesses. METHODS: We enrolled visitors at 4 freshwater Great Lakes beaches, and contacted them 10 to 12 days later to ask about health symptoms experienced since the visit. Water at the beaches was polluted by point sources that carried treated sewage. We tested water samples daily for Enterococcus using QPCR and membrane filtration (EPA Method 1600). RESULTS: We completed 21,015 interviews and tested 1359 water samples. Enterococcus QPCR cell equivalents (CEs) were positively associated with swimming-associated gastrointestinal (GI) illness (adjusted odds ratio per 1 log10 QPCR CE =1.26; 95% confidence interval = 1.06-1.51). The association between GI illness and QPCR CE was stronger among children aged 10 years and below (1.69; 1.24-2.30). Nonenteric illnesses were not consistently associated with Enterococcus QPCR CE exposure, although rash and earache occurred more frequently among swimmers. Enterococcus QPCR CE exposure was more strongly associated with GI illness than Enterococcus measured by membrane filtration. CONCLUSIONS: Measurement of the indicator bacteria Enterococci in recreational water using a rapid QPCR method predicted swimming-associated GI illness at freshwater beaches polluted by sewage discharge. Children at 10 years or younger were at greater risk for GI illness following exposure.     

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.     

Shigellosis from swimming in a park pond in Michigan

In July 1989 an outbreak of shigellosis occurred among visitors to a recreational park in Oakland County, MI. An epidemiologic investigation discovered an association between illness and swimming in a pond at the park, especially for those who had put their head underwater. No other factors were epidemiologically incriminated. A total of 65 cases were identified; nine were culture confirmed, all Shigella sonnei. Several water samples evaluated for fecal coliform counts shortly after the outbreak were found satisfactory. Cultures of water samples were negative for Shigella species. Inspection of the park's sewage disposal and toilet facilities found all equipment in proper working condition and no evidence of a sewage contamination event from these potential sources. No other commercial or residential sources of potential sewage contamination existed near the pond. Investigators concluded that Shigella contamination of the pond by a swimmer or swimmers on one or more occasions was a strong possibility. Factors supporting this conclusion included elevated incidence of S. sonnei in the community during the 2 months prior to the outbreak, greater use of the pond, warm water and air temperatures, and inadequate water exchange in the pond. This report adds one of the few documented outbreaks of shigellosis implicating bather contamination to the literature on the growing number of incidents that have been associated with recreational use of water.     

Phenotypic library-based microbial source tracking methods: efficacy in the California collaborative study

As part of a larger microbial source tracking (MST) study, several laboratories used library-based, phenotypic subtyping techniques to analyse fecal samples from known sources (human, sewage, cattle, dogs and gulls) and blinded water samples that were contaminated with the fecal sources. The methods used included antibiotic resistance analysis (ARA) of fecal streptococci, enterococci, fecal coliforms and E. coli; multiple antibiotic resistance (MAR) and Kirby-Bauer antibiotic susceptibility testing of E. coli; and carbon source utilization for fecal streptococci and E. coli. Libraries comprising phenotypic patterns of indicator bacteria isolated from known fecal sources were used to predict the sources of isolates from water samples that had been seeded with fecal material from the same sources as those used to create the libraries. The accuracy of fecal source identification in the water samples was assessed both with and without a cut-off termed the minimum detectable percentage (MDP). The libraries (approximately 300 isolates) were not large enough to avoid the artefact of source-independent grouping, but some important conclusions could still be drawn. Use of a MDP decreased the percentage of false-positive source identifications, and had little effect on the high percentage of true-positives in the most accurate libraries. In general, the methods were more prone to false-positive than to false-negative errors. The most accurate method, with a true-positive rate of 100% and a false-positive rate of 39% when analysed with a MDP, was ARA of fecal streptococci. The internal accuracy of the libraries did not correlate with the accuracy of source prediction in water samples, showing that one should not rely solely on parameters such as the average rate of correct classification of a library to indicate its predictive capabilities.     

Failure of indicator bacteria to reflect the occurrence of enteroviruses in marine waters.

The results of several studies conducted along the upper Texas Gulf coast, where a substantial amount of quantitative virological data were collected, are compared to bacteriological indicators and other environmental factors on a statistical basis. Variables common to all these studies were anlayzed by multivariate regression. Although multivariate analysis indicated that the number of viruses detected in water was related to rainfall, salinity, and total coliforms in the water, the amount of variation in the number of viruses accounted for by these factors was not large enough to make them good predictors. Enteroviruses were detected 43 per cent of the time in recreational waters considered acceptable as judged by coliform standards, and 44 per cent of the time when judged by fecal coliform standards. Enteroviruses were detected 35 per cent of the time in waters which met acceptable standards for shellfish-harvesting. Our failure to correlate the occurrence of enteroviruses in marine waters with indicator bacteria, and the frequent occurrence of enteroviruses in water which met current bacteriological standards, indicates that these standards do not reflect the occurrence of enteroviruses, and perhaps other human pathogenic viruses, in marine waters.     

Variations in microbial indicator densities in beach waters and health-related assessment of bathing water quality

Daily and hourly variations in microbial indicators densities in the beach-waters of Hong Kong have been described. The levels of Escherichia coli at a number of beaches was observed to be influenced by tide, and for staphylococci, by bather numbers. The tidal influence was most obvious during spring tides; and for the effect of bathers, during neap tides. Both organisms are present in high densities in external sources of faecal pollution of bathing beaches, with the average staphylococci to E. coli ratios being 0.04-3. Staphylococci may serve as an indicator of bather density and the risk of cross-infection amongst bathers (rather than as another indicator of faecal contamination) when the average staphylococci to E. coli ratio for a bathing beach is considerably higher than 3. The variability of microbial indicator densities means the routine sampling of bathing beaches should be carried out on weekend days with maximum numbers of swimmers exposed to the water, and spread throughout the bathing season.     

A prospective study of swimming-related illness. I. Swimming-associated health risk.

During the summer of 1980, both swimmers and nonswimmers were enlisted in a prospective epidemiological study to determine the relationship between swimming, water quality, and the incidence of illness. Results of 4,537 telephone follow-up interviews showed that crude morbidity rates were 69.6 per 1,000 swimmers versus 29.5 per 1,000 nonswimmers. Swimmers experienced respiratory ailments most frequently, followed by gastrointestinal, eye, ear, skin, and allergenic symptoms, respectively.