Morbidity and Mortality Weekly Report 

www.cdc.gov/mmwr 

Surveillance Summaries September 12, 2008 / Vol. 57 / No. SS-9 

Surveillance for Waterborne Disease 

and Outbreaks Associated with Recreational 

Water Use and Other Aquatic Facility-Associated 

Health Events — United States, 2005–2006 

and 

Surveillance for Waterborne Disease 

and Outbreaks Associated with Drinking Water 

and Water not Intended for Drinking — 

United States, 2005–2006 

department of health and human services


Centers for Disease Control and Prevention
 Centers for Disease Control and Prevention
MMWR
 

The MMWR series of publications is published by the Coordinating 

Center for Health Information and Service, Centers for Disease 

Control and Prevention (CDC), U.S. Department of Health and 

Human Services, Atlanta, GA 30333. 

Suggested Citation: Centers for Disease Control and Prevention. 

[Title]. Surveillance Summaries, [Date]. MMWR 2008;57(No. SS-#). 

Centers for Disease Control and Prevention 

Julie L. Gerberding, MD, MPH 

Director 

Tanja Popovic, MD, PhD 

Chief Science Officer 

James W. Stephens, PhD 

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Director, National Center for Health Marketing 

Katherine L. Daniel, PhD 

Deputy Director, National Center for Health Marketing 

Editorial and Production Staff 

Frederic E. Shaw, MD, JD 

Editor, MMWR Series
 

Susan F. Davis, MD
 

(Acting) Assistant Editor, MMWR Series
 

Teresa F. Rutledge
 

Managing Editor, MMWR Series
 

David C. Johnson
 

(Acting) Lead Technical Writer-Editor
 

Patricia A. McGee
 

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Stephen R. Spriggs 

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Quang M. Doan, MBA
 

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Editorial Board 

William L. Roper, MD, MPH, Chapel Hill, NC, Chairman
 

Virginia A. Caine, MD, Indianapolis, IN
 

David W. Fleming, MD, Seattle, WA
 

William E. Halperin, MD, DrPH, MPH, Newark, NJ
 

Margaret A. Hamburg, MD, Washington, DC
 

King K. Holmes, MD, PhD, Seattle, WA
 

Deborah Holtzman, PhD, Atlanta, GA
 

John K. Iglehart, Bethesda, MD
 

Dennis G. Maki, MD, Madison, WI
 

Sue Mallonee, MPH, Oklahoma City, OK
 

Patricia Quinlisk, MD, MPH, Des Moines, IA
 

Patrick L. Remington, MD, MPH, Madison, WI
 

Barbara K. Rimer, DrPH, Chapel Hill, NC
 

John V. Rullan, MD, MPH, San Juan, PR
 

William Schaffner, MD, Nashville, TN
 

Anne Schuchat, MD, Atlanta, GA
 

Dixie E. Snider, MD, MPH, Atlanta, GA
 

John W. Ward, MD, Atlanta, GA
 

CONTENTS
 

Surveillance for Waterborne Disease and Outbreaks 

Associated with Recreational Water Use and Other 

Aquatic Facility-Associated Health Events — 

United States, 2005–2006 

Introduction ......................................................................... 2
 

Background ......................................................................... 3
 

Methods .............................................................................. 4
 

Results ................................................................................. 6
 

Discussion ......................................................................... 14
 

Conclusion ........................................................................ 25
 

References ......................................................................... 26
 

Appendices ....................................................................... 30
 

Surveillance for Waterborne Disease and Outbreaks 

Associated with Drinking Water and Water not 

Intended for Drinking — United States, 2005–2006 

Introduction ....................................................................... 39
 

Background ....................................................................... 40
 

Methods ............................................................................ 41
 

Results ............................................................................... 44
 

Discussion ......................................................................... 52
 

Conclusion ........................................................................ 59
 

References ......................................................................... 61
 

Appendices ....................................................................... 63
 

On the Cover (left to right): A child filling a cup with tap water. A 

man standing in a natural body of water. Young children playing in 

a swimming pool. 
Vol. 57 / SS-9	 Surveillance Summaries 1 

Surveillance for Waterborne Disease and Outbreaks Associated 

with Recreational Water Use and Other Aquatic Facility-Associated 

Health Events — United States, 2005–2006 

Jonathan S. Yoder, MSW, MPH1
 

Michele C. Hlavsa, MPH1
 

Gunther F. Craun, MPH2
 

Vincent Hill, PhD1
 

Virginia Roberts, MSPH1,3
 

Patricia A. Yu, MPH4
 

Lauri A. Hicks, DO5
 

Nicole T. Alexander, MPH5
 

Rebecca L. Calderon, PhD6
 

Sharon L. Roy, MD1
 

Michael J. Beach, PhD1
 

1Division of Parasitic Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, CDC
 

2Gunther F. Craun and Associates, Staunton, Virginia


3Atlanta Research and Education Foundation
 

4Division of Foodborne, Bacterial, and Mycotic Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, CDC
 5Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases
 6U.S. Environmental Protection Agency, Research Triangle Park, North Carolina
 

Abstract

Problem/Condition: Since 1971, CDC, the U.S. Environmental Protection Agency, and the Council of State and 

Territorial Epidemiologists have collaboratively maintained the Waterborne Disease and Outbreak Surveillance System 

for collecting and reporting data related to waterborne-disease outbreaks (WBDOs) associated with drinking water. In 

1978, WBDOs associated with recreational water (natural and treated water) were added. This system is the primary 

source of data regarding the scope and effects of disease associated with recreational water in the United States. In 

addition, data are collected on individual cases of recreational water-associated illnesses and infections and health 

events occurring at aquatic facilities but not directly related to water exposure. 

Reporting Period: Data presented summarize WBDOs and case reports associated with recreational water use that occurred 

during January 2005–December 2006 and previously unreported disease reports and outbreaks during 1978–2004. 

Description of the System: Public health departments in the states, territories, localities, and the Freely Associated 

States (i.e., the Republic of the Marshall Islands, the Federated States of Micronesia, and the Republic of Palau, 

formerly parts of the U.S.-administered Trust Territory of the Pacific Islands) have primary responsibility for detecting, 

investigating, and voluntarily reporting WBDOs to CDC. Although the surveillance system includes data for WBDOs 

and cases associated with drinking water, recreational water, and water not intended for drinking, only cases and 

outbreaks associated with recreational water and health events at aquatic facilities are summarized in this report. 

Results: During 2005–2006, a total of 78 WBDOs associated with recreational water were reported by 31 states. 

Illness occurred in 4,412 persons, resulting in 116 hospitalizations and five deaths. The median outbreak size was 13 

persons (range: 2–2,307 persons). Of the 78 WBDOs, 48 (61.5%) were outbreaks of gastroenteritis that resulted from 

infectious agents or chemicals; 11 (14.1%) were outbreaks of acute respiratory illness; and 11 (14.1%) were outbreaks 

of dermatitis or other skin conditions. The remaining eight were outbreaks of leptospirosis (n = two), primary amebic 

meningoencephalitis (n = one), and mixed or other illnesses (n = five). WBDOs associated with gastroenteritis resulted 

in 4,015 (91.0%) of 4,412 illnesses. Fifty-eight (74.4%) WBDOs occurred at treated water venues, resulting in 4,167 

(94.4%) cases of illness. The etiologic agent was confirmed in 62 (79.5%) of the 78 WBDOs, suspected in 12 (15.4%), 

and unidentified in four (5.1%). Thirty-four (43.6%) WBDOs had a parasitic etiology; 22 (28.2%), bacterial; four 

(5.1%), viral; and two (2.6%), chemical or toxin. Among 

the 48 gastroenteritis outbreaks, Cryptosporidium was 

Corresponding author: Jonathan S. Yoder, MSW, MPH, Division of Parasitic confirmed as the causal agent in 31 (64.6%), and all Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, 4770 

Buford Hwy., NE, MS F-22, Atlanta, GA 30341. Telephone: 770-488-3602; except two of these outbreaks occurred in treated water 

Fax: 770-488-7761. E-mail: jey9@cdc.gov.	 venues where Cryptosporidium caused 82.9% (29/35) of
 

the gastroenteritis outbreaks.
 
2 MMWR September 12, 2008 

Case reports associated with recreational water exposure that were discussed and analyzed separately from outbreaks 

include three fatal Naegleria cases and 189 Vibrio illnesses reported to the Cholera and Other Vibrio Illness Surveillance 

System. For Vibrio reporting, the most commonly reported species were Vibrio vulnificus, V. alginolyticus, and V. parahaemolyticus. 

V. vulnificus illnesses associated with recreational water exposure had the highest Vibrio illness hospitalization (77.6%) 

and mortality (22.4%) rates. 

In addition, 32 aquatic facility-related health events not associated with recreational water use (e.g., pool chemical 

mixing accidents) that occurred during 1983–2006 were received from New York. These events, which caused illness in 

364 persons, are included in this report but analyzed separately. 

Interpretations: The number of WBDOs summarized in this report and the trends in recreational water-associated 

disease and outbreaks demonstrate a substantial increase in number of reports from previous years. Outbreaks, especially the largest ones, occurred more frequently in the summer at treated water venues and caused gastrointestinal 

illness. Deficiencies leading to WBDOs included problems with water-quality, venue design, usage, and maintenance. 

Case reports of illness associated with recreational water use expand our understanding of the scope of waterborne 

illness by further underscoring the contribution of less well-recognized swimming venues (e.g., oceans) and illness 

(e.g., nongastrointestinal illness). Aquatic facilities are also a focus for injuries involving chemicals or equipment used 

routinely in the operation of swimming venues, thus illustrating the lack of training of some aquatics staff. 

Public Health Actions: CDC uses WBDO surveillance data to 1) identify the etiologic agents, types of aquatic 

venues, water-treatment systems, and deficiencies associated with outbreaks and case reports; 2) evaluate the adequacy 

of efforts (i.e., regulations and public awareness activities) to provide safe recreational water; 3) expand the scope of 

understanding about waterborne disease and health events associated with swimming and aquatics facilities; and 4) 

establish public health prevention priorities, data, and messaging that might lead to improved regulations, guidelines, 

and prevention measures at the local, state, and federal levels. 

Introduction 

During 1920–1970, statistical data regarding waterbornedisease outbreaks (WBDOs) in the United States were collected by different researchers and federal agencies (1). Since 

1971, CDC, the U.S. Environmental Protection Agency 

(EPA), and the Council of State and Territorial Epidemiologists (CSTE) have collaboratively maintained the Waterborne 

Disease and Outbreak Surveillance System (WBDOSS), a 

surveillance system that tracks the occurrences and causes of 

WBDOs and cases of disease associated with drinking water 

(2–11). In 1978, WBDOs associated with recreational water 

were added to the surveillance system. The types of outbreaks 

and disease case reports included in the Surveillance Summaries have expanded multiple times to more accurately reflect 

the scope of waterborne disease in the United States. Outbreaks of Pontiac fever (PF) were added in 1989 (9), outbreaks of Legionnaires’ disease (LD)were added in 2001 (3,12), 

and single cases of Vibrio illness reported to the Cholera and 

Other Vibrio Illness Surveillance System that were associated 

with recreational water use were added in 2003. WBDOs 

associated with drinking water and water not intended for 

drinking are presented in a separate report (13). 

WBDO surveillance activities are intended to 1) characterize the epidemiology of waterborne disease; 2) identify trends 

in the etiologic agents and other factors associated with

WBDOs; 3) identify major deficiencies in providing safe recreational water; 4) encourage public health personnel to 

detect and investigate WBDOs; 5) foster collaboration among 

local, state, federal, and international agencies on initiatives

to prevent waterborne disease; and 6) collect data needed to 

support future prevention efforts. Additional data on cases of 

waterborne disease related to recreational water are gathered 

from separate disease surveillance systems and through supplementary surveillance activities (Figure 1). Some of these data 

are collected and analyzed in WBDOSS, and some are discussed in this report. These data are useful for expanding our 

understanding of the scope of waterborne disease, identifying

important factors associated with unsafe or unhealthy recreational water, influencing research priorities, supporting public health recommendations, and encouraging improved 

water-quality policies and regulations. However, WBDOs and 

case reports summarized in this report are thought to represent only a portion of the illness associated with recreational 

water exposure. Reliable estimates of the number of unrecognized WBDOs are not available. In addition, the surveillance 

information described in this report does not include estimates of the number of recreational water illnesses (RWIs). 
Vol. 57 / SS-9 Surveillance Summaries 3 

FIGURE 1. Data sources and outputs of the Waterborne Disease and Outbreak Surveillance System 

Waterborne disease outbreaks (WBDOs) 

reported routinely to CDC by jurisdictional 

health authorities (e.g., states and territories) 

Single water-associated cases of 

• Primary Amebic Meningoencephalitis 

(e.g., ) 

• Chemical/toxin poisoning 

• Wound infections (reported sporadically 

by some jurisdictional health authorities) 

Naegleria fowleri 

Aquatic facility-related health events not 

associated with recreational water 

(reported sporadically by jurisdictional 

health authorities) 

Recreational water-associated Vibrio cases 

(reported separately to the Cholera and 

Other Surveillance System) Vibrio 

Periodic reports of waterbornedisease outbreaks 

Waterborne Disease and Outbreak 

(recreational, drinking, and other 

uses) published biennially in 

Surveillance Summaries 

MMWR 

Analysis of waterborne disease and outbreaks and 

dissemination of waterborne-disease prevention messages 

Waterborne Disease 

and Outbreak Surveillance 

System (WBDOSS) 

Use of surveillance data by public 

health researchers and policy 

makers to understand and reduce 

waterborne disease and outbreaks 

Background EPA sets guidelines for recreational use of natural waters 

(e.g., lakes, rivers, and oceans). In 1986, EPA developed recRegulation of Recreational Water ommended bacterial water-quality criteria for coastal recreQuality ation waters (16) and recently established federal standards 

for those states and territories that have not yet adopted In the United States, state and local governments establish water-quality criteria that meet or exceed the 1986 criteria and enforce regulations for protecting recreational water from (17). For freshwater, full-body contact beaches (e.g., lakes and naturally occurring or human-made contaminants. For treated rivers), EPA has recommended that the monthly geometric water venues (e.g., swimming pools and water parks), no fed­ mean water-quality indicator concentration be <33 CFU/100 

eral regulatory agency has authority, and no national guide­ mL for enterococci or <126 CFU/100 mL for Escherichia coli. lines for standards of design, construction, operation, For marine-water, full-body contact beaches, EPA has recom­ disinfection, or filtration exist, except recent regulation to pre­ mended that the monthly geometric mean water-quality vent entrapment injuries (14). Swimming pool codes are indicator concentration be <35 CFU/100 mL for enterococci. 

developed and enforced by state and local health departments; However, state and local authorities have discretionary therefore, substantial variation is observed across the country authority to determine which interventions should be used in terms of policy, compliance, and enforcement (15). Efforts (e.g., posting signs to alert visitors of water contamination or are underway to develop a Model Aquatic Health Code (avail­ closing the beach for swimming) when these limits have been able at http://www.cdc.gov/healthyswimming/model_code.htm) exceeded. Beach Watch, EPA’s Action Plan for Beaches and 

to be used as a national voluntary guideline. These data-driven Recreational Waters (report available at http://www.epa.gov/ and knowledge-based guidelines will be focused on promot­ waterscience/beaches/technical.html), was published in 1999 ing healthy recreational water experiences by preventing dis­ as part of the Clean Water Action Plan (available at http:// ease and injuries. The model code will be available to state www.epa.gov/beaches). The intent of Beach Watch is to assist and local health agencies needing guidance in writing, updat­ state, tribal, and local authorities in strengthening and extend­ ing, and implementing state or local pool codes and might ing existing programs to protect users of fresh and marine rec­ help standardize pool codes across the United States. reational waters; as part of the BEACH Act of 2000, the U.S. 

Congress directed EPA to update its guidelines for recreational 
4 MMWR September 12, 2008 

water use on the basis of improved water-quality indicators and 

testing. As a result, EPA has been collaborating with CDC since 

2002 on the National Epidemiologic and Environmental 

Assessment of Recreational (NEEAR) Water Study at fresh and 

marine water recreational beaches in the United States. Information on the NEEAR is available at http://www.epa.gov/ 

nheerl/neear. This study is being conducted to evaluate rapid 

new water-quality methods that are able to produce results in 

<2 hours and to correlate these indicators with health effects 

among beachgoers. Results from freshwater Great Lakes beaches 

have demonstrated an association between an increasing signal 

detected by a quantitative polymerase chain reaction-based test 

method for enterococci and human health effects (18, 19). 

Children aged <10 years were at greater risk for gastrointestinal 

illness following exposure (19) to water with elevated levels of 

enterococci. 

Methods 

Data Sources 

Public health departments in individual states, territories, 

localities, and the Freely Associated States (FAS)* have the 

primary responsibility for detection and investigation of 

WBDOs. The outbreaks are voluntarily reported to CDC 

through a standard form (i.e., CDC form 52.12; available at 

http://www.cdc.gov/healthyswimming/downloads/cdc_5212_ 

waterborne.pdf). The form solicits data on WBDO, including characteristics of person, place, and time and results of 

epidemiologic studies, disease symptoms, diagnostic testing, 

and water sampling. Information gathered regarding the setting of the outbreak includes the type of aquatic facility, water 

source and treatment, sanitary measures in place, and possible factors contributing to the contamination of the water. 

Public health professionals in each state or locality are designated as WBDO surveillance coordinators, and CDC annually requests reports from coordinators in all states and localities 

and conducts as much follow-up correspondence as needed 

to resolve unaddressed questions. Although national reporting only includes WBDOs, single cases of certain waterborne 

diseases (e.g., primary amebic meningoencephalitis (PAM) and 

chemical toxin poisoning) are also solicited from coordinators. Outbreaks, cases, or other health events, where applicable, are assigned to a state on the basis of the location of the 

exposure rather than state of residence of ill persons. Numeric 

and text data from the CDC waterborne disease outbreak form 

and any supporting documentation are entered into a data­

* Composed of the Republic of the Marshall Islands, the Federated States of 

Micronesia, and the Republic of Palau; formerly parts of the U.S.-administered 

Trust Territory of the Pacific Islands. 

base for analysis. Although all WBDOs are collected through 

the same CDC reporting system, the recreational waterassociated outbreaks are analyzed and published separately 

from drinking water-associated outbreaks and other WBDOs 

(13). Information on WBDOs and cases is sometimes solicited from other CDC surveillance systems and confirmed with 

the state or locality for inclusion in WBDOSS or Surveillance 

Summary (Figure 1). Vibrio illnesses associated with recreational 

water exposure were received from the Cholera and Other 

Vibrio Illness Surveillance System. 

Definitions† 

Waterborne Disease Outbreaks 

The unit of analysis for the summary is an outbreak, not an 

individual case of a waterborne disease. To be defined as a 

WBDO associated with recreational water, an event must meet 

two criteria. First, two or more persons must be epidemiologically linked by the location of the exposure to recreational 

water, time, and illness. Recreational water settings include 

swimming pools, wading pools, spas, waterslides, interactive 

fountains, wet decks, and fresh and marine bodies of water. 

Second, the epidemiologic evidence must implicate water or 

volatilization of water-associated compounds into the air surrounding an aquatic facility as the probable source of the illness. For this report, WBDOs are separated by venue as 

untreated (i.e., fresh and marine surface water) or treated (i.e., 

filtered or disinfected [e.g., chlorinated]) water. WBDOs 

associated with ships are not included in this report. 

Case Reports of Waterborne Illness or 

Reports of Aquatic Facility-Associated 

Health Events 

This report also includes 1) individual cases of laboratoryconfirmed PAM associated with recreational water use, 2) 

single cases of wound infections or other Vibrio infections associated with recreational water use, 3) single cases of chemical and toxin poisoning if water or air-quality data indicate 

contamination by the chemical or toxin, and 4) outbreaks or 

case reports of health events associated with aquatic facilities 

but not associated with the recreational water but rather contaminated aquatic facility air (e.g., mixing of chemicals in the 

pump room might release toxic gas that injures staff or facility users) (Figure 1). Because these four event categories do 

not meet WBDO definition, they are analyzed separately from 

WBDOs. 

† Additional terms have been defined (Appendix A, Glossary of Definitions). 
Vol. 57 / SS-9 Surveillance Summaries 5 

Strength of Evidence Classification for 

Waterborne-Disease Outbreaks 

WBDOs reported to WBDOSS are classified according to 

the strength of evidence that implicates water as the vehicle of 

transmission (Table 1). The classification scheme (i.e., Classes 

I–IV) is based on the epidemiologic and water-quality data 

provided on WBDO report form. Although in certain 

instances WBDOs without water-quality data were included 

in this report, outbreaks that lacked any epidemiologic data 

linking the outbreak to water were excluded. 

Class I indicates that adequate epidemiologic and waterquality data were reported (Table 1). However, the classification does not necessarily imply that an investigation was 

conducted optimally. Likewise, a classification of II, III, or IV 

does not imply that an investigation was inadequate or 

incomplete. Outbreaks and investigations occur under varying circumstances, and not all outbreaks can or should be rigorously investigated. In addition, outbreaks that affect fewer 

persons are more likely to receive classifications of III or IV 

because of the limited sample size available for data analysis. 

Changes in the 2005–2006 Surveillance

Summary

The definition of a waterborne outbreak has been modified 

for this report to be consistent with generally accepted public 

health practice (i.e., two or more epidemiologically linked cases 

associated with use of recreational water). Health events at 

aquatic facilities not associated with direct exposures to recreational water are, for the first time, presented and discussed 

but not analyzed as waterborne outbreaks. 

Definition 

Previously, the definition of a recreational waterborne disease outbreak included certain single cases of waterborne disease. The definition of a recreational waterborne-disease 

outbreak has been clarified to include two or more persons 

who have been epidemiologically linked to recreational water 

by location of exposure, time, and illness. Exposures include 

contact with or accidental ingestion of water and certain 

inhalation exposures (e.g., exposure to water-associated compounds [e.g., chloramines] volatilizing into the air of the 

aquatic facility). Single cases of PAM, recreational waterassociated Vibrio illness, and illness related to chemical exposure caused by water are included in WBDOSS but are not 

classified or analyzed as outbreaks. These single cases are 

analyzed separately. 

Aquatic Facility-Related Health Events 

not Associated with Recreational Water 

Previous Surveillance Summaries only included outbreaks in 

which the vehicle of transmission was water or airborne chemical products originating from water (e.g., chloramines). 

Nonwater-related illnesses resulting from chemical inhalation 

or exposure at aquatic facilities have not been discussed in 

previous Surveillance Summaries. This report includes, as a 

separate analysis, chemical injury (e.g., mixing of pool chemicals that release toxic gas) cases and outbreaks at aquatic 

facilities in which direct exposure to water was not the cause 

of illness. Whereas these events are not classified or analyzed 

as waterborne outbreaks, they highlight important public 

health and safety concerns related to the design, operation, 

and maintenance of recreational water venues and are targeted 

to the same audiences who are the focus of the waterborne 

disease and outbreaks already included in this report. 

TABLE 1. Classification of investigations of waterborne-disease outbreaks based on strength of evidence inplicating water as 

the vehicle of transmission — United States 

Class Epidemiologic data Water-quality data 

I 

II 

III 

IV 

Adequate 

Data provided about exposed and unexposed persons, 

with relative risk or odds ratio >2 or p-value <0.05 

Adequate 

Provided but limited 

Epidemiologic data provided that did not meet the 

criteria for Class I, or claim made that ill persons 

had no exposures in common, besides water, 

but no data provided 

Provided but limited 

Provided and adequate 

Laboratory data or historical information (e.g., the history that a 

chlorinator or pH acid feed pump malfunctioned, no detectable 

free-chlorine residual, or a breakdown in a recirculation system) 

Not provided or inadequate (e.g., laboratory testing of water not 

conducted and no historical information) 

Provided and adequate 

Not provided or inadequate 
6 MMWR September 12, 2008 

Results 

Waterborne-Disease Outbreaks 

Excluding Vibrio and PAM cases and aquatic facility-related 

health events, a total of 78 outbreaks (38 in 2005 and 40 in 

2006) associated with recreational water were reported to CDC 

(Tables 2–5). This is the highest number of outbreaks reported 

for a 2-year summary since reporting began in 1978. Of the 

50 states and 10 territories, localities, and FAS participating 

in WBDOSS, 31 states reported WBDOs (Figure 2). Descriptions of selected WBDOs are presented in this report 

(Appendix B, Selected Descriptions of Waterborne Disease 

and Outbreaks [WBDOs] Associated with Recreational 

Water). These 78 outbreaks affected 4,412 persons and 

resulted in five deaths. The median outbreak size was 13 persons (range: 2–2,307 persons). Minnesota reported the highest number of WBDOs (nine), New York and Florida each 

reported seven WBDOs, and Wisconsin reported six WBDOs. 

During 2005–2006, treated water venues were associated 

with 58 (74.4%) of the recreational water outbreaks and 4,167 

(94.4%) of the cases (Tables 2 and 3; Figure 3). Untreated 

venues were associated with 20 (25.6%) of WBDOs but only 

245 (5.6%) of the cases (Tables 4 and 5). 

Of the 78 WBDOs, 48 (61.5%) were outbreaks of acute gastroenteritis illness (AGI), 11 (14.1%) were outbreaks of dermatitis or other skin conditions, and 11 (14.1%) were outbreaks of 

acute respiratory illness (ARI). The remaining WBDOs resulted 

in leptospirosis (n = two), PAM (n = one), and mixed or other 

illnesses (n = five) (Table 6, Figure 3). WBDOs associated with 

gastroenteritis accounted for 4,015 (91.0%) of the cases of illness. The route of entry implicated for each WBDO was ingestion for 48 outbreaks (61.5%), inhalation for 10 (12.8%), contact 

for 8 (10.3%), combined routes for nine (11.5%), and other 

(Naegleria and Leptospira) for three (3.8%) Figure 3). 

WBDOs occurred in every calendar month. However, the 

summer months (June through August) accounted for 51 

(65.4%) WBDOs and 3,890 (88.2%) cases (Figure 4). Gastroenteritis was particularly clustered during these months with 

40/48 (83.3%) outbreaks and 3,777/4,015 (94.1%) cases 

being reported. 

TABLE 2. Waterborne-disease outbreaks (n = 24) associated with treated recreational water, by state — United States, 2005 

No. of cases 

State Month Class* Etiologic agent 

Predominant 

illness† 

(deaths) 

(n = 3,376) Type Setting 

Connecticut Apr I Pseudomonas aeruginosa Skin 4 Pool, Spa Hotel 

Florida Jun II Cryptosporidium AGI 47 Pool Hotel 

Iowa Jun II Cryptosporidium AGI 24 Pool Community 

Kansas Jul II Cryptosporidium AGI 84 Pool Water park 

Kentucky Jun IV Cryptosporidium AGI 53 Pools Community 

Kentucky Jun IV Cryptosporidium AGI 9 Pool, wading pool Community 

Louisiana Aug IV Cryptosporidium AGI 31 Interactive fountain Water park 

Massachusetts Jul III Giardia intestinalis AGI 11 Pool Membership club 

Minnesota May II Unidentified AGI 32 Pool, spa Membership club 

Minnesota Aug IV Legionella pneumophila serogroup 1 ARI 3 Spa Private residence 

Minnesota Apr I Unidentified§ ARI, eye 20 Pool, spa Hotel 

Minnesota Mar IV Unidentified¶ Skin 8 Spa Hotel 

North Carolina Apr III L. pneumophila serogroup 1 ARI 4 (1) Spa Private residence 

New Mexico Apr III P. aeruginosa Skin, ear 7 Pool, spa Hotel 

New York Aug II Cryptosporidium AGI 97 Pool Camp 

New York Oct III Cryptosporidium AGI 22 Pool Membership club 

New York Jun I C. hominis** AGI 2,307 Interactive fountain State park 

Ohio Jul III Chlorine gas†† ARI 19 Pool Community 

Ohio Aug III C. hominis AGI 523 Pools Community 

Oregon Jul II C. parvum AGI 20 Pool Membership club 

South Carolina Oct III L. pneumophila§§ ARI 18 Spa Hotel 

Vermont Feb IV Unidentified¶ Skin 18 Spa Hotel 

Wisconsin Jul I P. aeruginosa Skin 9 Pool, Spa Hotel 

Wyoming Jul IV Campylobacter jejuni AGI 6 Kiddie pool Private residence 

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12 (available at http://www.cdc.gov/healthyswimming/downloads/ 

cdc_5212_waterborne.pdf) (see Table 1). 

† Skin: illness, condition, or symptom related to skin; AGI: acute gastrointestinal illness; ARI: acute respiratory illness; Eye: illness, condition, or symptom 

related to eyes; and Ear: illness, condition, or symptom related to ears.
 

§ Etiology unidentified: contamination from excess chlorine levels or pool disinfection by-products (e.g., chloramines) suspected.
 ¶ Etiology unidentified: P. aeruginosa suspected on the basis of clinical syndrome and setting.
 

** Species determined using molecular technology and current taxonomic guidelines (Source: Xiao L, Ryan UM. 2008: Molecular epidemiology, 

In: Cryptosporidium and cryptosporidiosis. Fayer R, Xiao L, eds. Boca Raton, Florida: CRC Press; 2008:119-71). 

†† Chlorine gas was released after high levels of liquid chlorine and acid were mixed in the recirculation system and subsequently released into the pool water. §§ Fifteen persons were diagnosed with Pontiac fever and three persons were diagnosed with Legionnaires' disease. 
Vol. 57 / SS-9	 Surveillance Summaries 7 

TABLE 3. Waterborne-disease outbreaks (n = 34) associated with treated recreational water, by state — United States, 2006 

No. of cases 

State Month Class* Etiologic agent 

Predominant 

illness† 

(deaths) 

(n = 791) Type Setting 

Arkansas Jul I Legionella pneumophila§ ARI 37 Pool, spa Hotel 

California Jul II Shigella sonnei AGI 9 Kiddie pool Private residence 

California Jul III Cryptosporidium¶ AGI 16 Interactive fountain Community 

Colorado Aug II Cryptosporidium** AGI 12 Pool Community 

Colorado Oct II L. pneumophila serogroup 1†† ARI 6 Spa Private home 

Florida Jan I L. pneumophila serogroup 1 ARI 11 (1) Spa Hotel 

Florida May III Giardia, Cryptosporidium§§ AGI 55 Interactive fountain Community 

Florida Aug IV Cryptosporidium AGI 3 Pool Hotel 

Georgia Aug IV Cryptosporidium AGI 19 Pool Community 

Georgia Feb IV Unidentified ¶¶ Skin 4 Spa Cabin 

Georgia Oct IV Cryptosporidium AGI 4 Pool Community 

Illinois Jan I Legionella*** ARI 43 (1) Pool, spa Hotel 

Illinois Jul I C. hominis** AGI 65 Pool Day camp, water park 

Illinois Jun III Unidentified††† Skin 9 Pool Community 

Illinois Aug IV Cryptosporidium AGI 4 Pool Water park 

Illinois Aug IV Cryptosporidium AGI 18 Pool Water park 

Indiana Apr IV Unidentified ARI, ear 12 Pool Membership club 

Kansas Dec IV Pseudomonas aeruginosa Skin 8 Spa Private residence 

Louisiana Jul II Cryptosporidium** AGI 29 Pool, interactive fountain Water park 

Minnesota Sep II C. hominis AGI 47 Pool Schools 

Missouri Jul IV Cryptosporidium AGI 6 Pool Community 

Missouri Jun III Cryptosporidium AGI 116 Pool, interactive fountain Water park 

Montana Jul IV Cryptosporidium AGI 82 Pools Community 

Nebraska Dec III Unidentified§§§ ¶¶¶ ARI, eye 24 Pool Hotel 

New York Oct III L. pneumophila serogroup 1 ARI 2 Spa Water park 

New York Mar IV Unidentified§§§ ARI 9 Pool Water park 

Pennsylvania Jun IV Cryptosporidium AGI 13 Pool Membership club 

South Carolina Jul III C. hominis** AGI 12 Pool Community 

Tennessee Mar IV Unidentified¶¶ Skin 15 Pool, spa Hotel 

Wisconsin Feb III Unidentified ¶¶ Skin 28 Pool, spa Hotel 

Wisconsin May I Norovirus AGI 18 Pool Hotel 

Wisconsin Aug II Cryptosporidium AGI 22 Pool Campground 

Wisconsin Aug IV Cryptosporidium AGI 4 Pool Community 

Wyoming Jun II Cryptosporidium** AGI 29 Pools**** Community 

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12 (available at http://www.cdc.gov/healthyswimming/downloads/ 

cdc_5212_waterborne.pdf) (see Table 1). 

† ARI: acute respiratory illness; AGI: acute gastrointestinal illness; Skin: illness, condition, or symptom related to skin; Ear: illness, condition, or 

symptom related to ears; and Eye: illness, condition, or symptom related to eyes.

§ Pontiac fever was diagnosed in 34 persons, and Legionnaires’ disease was diagnosed in three persons.

¶ Eleven pulsed-field gel electrophoresis-matched cases of Salmonella stanley were also detected among persons who visited the fountain 

during this outbreak; however, the outbreak investigation did not rule out other possible common exposures among those case-patients. 

** Source: CDC. Cryptosporidiosis outbreaks associated with recreational water use — five states, 2006. MMWR 2007;56:729–32. †† All cases were diagnosed as Pontiac fever. §§ Thirty-five persons had stool specimens that tested positive for Giardia, seven persons had stool specimens that tested positive for 

Cryptosporidium, and two persons had stool specimens that tested positive for both Giardia and Cryptosporidium. ¶¶ Etiology unidentified: Pseudomonas aeruginosa suspected on the basis of clinical syndrome and setting. 

*** Pontiac fever was diagnosed in 40 persons, and Legionnaires’ disease was diagnosed in three persons. L. pneumophila and L. maceachernii 

were detected in both pool and spa water. 

††† Etiology unidentified: low pH suspected on the basis of water testing and symptoms.
 §§§ Etiology unidentified: chemical contamination from pool disinfection by-products (e.g., chloramines) suspected.
 ¶¶¶ Source: CDC. Ocular and respiratory illness associated with an indoor swimming pool—Nebraska, 2006. MMWR 2007;56:929–32.
 

**** Case-patients identified in this outbreak reported exposure to multiple community pools and to an untreated reservoir.
 

Etiologic Agents	 parasites; 22 (28.2%), bacteria; four (5.1%), viruses; and two 

Of the 78 WBDOs associated with recreational water, the (2.6%), chemicals (Figure 3). 

Of the 47 outbreaks associated with treated water venues etiologic agent was confirmed in 62 (79.5%), suspected in 12 with an identified etiologic agent: 31 (66.0%) involved para­ (15.4%) and unidentified in four (5.1%) (Table 7). Thirty- sites; 14 (29.8%), bacteria; one (2.1%), a virus; and one (2.1%) four (43.6%) outbreaks were confirmed as being caused by 
8 MMWR September 12, 2008 

TABLE 4. Waterborne-disease outbreaks (n = 14) associated with untreated recreational water, by state — United States, 2005 

No. of cases 

Predominant† (deaths) 

State Month Class* Etiologic agent illness (n = 171) Type Setting 

California Jul IV Unidentified § Skin 2 Lake Lake 

California Jul IV Leptospira Lep 3 Stream Stream 

Florida Jul I Unidentified ¶ Other 24 Ocean¶ Beach 

Florida Nov II Leptospira Lep 43 Stream Adventure race 

Maine Jul III Unidentified AGI 10 Lake Swimming beach 

Massachusetts Jul IV Shigella sonnei AGI 5 Lake Lake 

Michigan Jun IV Copper sulfate ARI 3 Lake Lake 

Minnesota Jun IV Escherichia coli O157:H7 AGI 4 Lake Swimming beach 

Minnesota Jul IV S. sonnei AGI 12 Lake Swimming beach 

Minnesota Aug IV Norovirus AGI 8 Lake Swimming beach 

New York Jul III Cryptosporidium AGI 27 Lake Swimming beach 

New York Aug III Unidentified** AGI 13 Lake Lake 

Oklahoma Jul IV Naegleria fowleri Neuro 2 (2) Unknown†† Unknown 

Pennsylvania Jul IV S. sonnei AGI 15 Lake Swimming beach 

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12 (available at http://www.cdc.gov/healthyswimming/downloads/ 

cdc_5212_waterborne.pdf) (see Table 1). 

† Skin: illness, condition, or symptom related to skin; Lep: leptospirosis; Other: undefined or mixed illness, condition, or symptom. AGI: acute gastrointestinal illness; ARI: acute respiratory illness; Skin: illness, condition, or symptom related to skin; and Neuro: neurologic condition or symptoms (e.g. 

meningitis). 

§ Etiology unidentified: clinical diagnosis of cercarial dermatitis (caused by avian schistosomes). 

¶ Etiology unidentified: whereas certain swimmers had symptoms consistent with seabathers eruption (caused by jellyfish larvae), a majority of persons 

affected in this outbreak experienced systemic, flu-like illnesses which might have been related to another etiology. Swimmers alternated between marine 

and chlorinated swimming venues. 

** Etiology unidentified: Illness was most consistent with norovirus infection on the basis of clinical syndrome. 

†† Whereas an interactive fountain at a water park was a common exposure for both case-patients, other potentially shared and untreated recreational water 

exposures could not be ruled out. 

TABLE 5. Waterborne-disease outbreaks (n = six) associated with untreated recreational water, by state — United States, 2006 

Predominant No. of cases 

State Month Class* Etiologic agent illness † (n = 74) Type Setting 

Florida May II Norovirus G2 AGI 50 Lake Swimming beach 

Massachusetts Aug III Cryptosporidium AGI 6 Pond Camp 

Minnesota May II Norovirus G1 AGI 10 Lake Private beach 

Ohio Aug IV Unidentified§ Skin 2 Pond Pond 

Tennessee Jul IV Escherichia coli O157:H7 AGI 3 Lake Swimming beach 

Wisconsin Jun IV E. coli O157:H7 AGI 3 Lake State park 

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12 (available at http://www.cdc.gov/healthyswimming/downloads/ 

cdc_5212_waterborne.pdf) (and Table 1). 

†AGI: acute gastrointestinal illness; and Skin: illness, condition, or symptom related to skin. 

§Etiology unidentified: clinical diagnosis of cercarial dermatitis (caused by avian schistosomes). 

a chemical (Table 7). Parasites were responsible for approximately 20 times more cases than bacteria (3,784 versus 167). 

Of the 15 WBDOs associated with untreated water venues 

with an identified etiologic agent, eight (53.3%) involved 

bacteria; three (20.0%) parasites; three (20.0%) viruses; and 

one (6.7%) a chemical. 

Parasites 

Of the 48 outbreaks of gastroenteritis, 33 (68.8%) were 

parasitic in origin, including 31 (93.9%) caused by 

Cryptosporidium, one (3.0%) caused by Giardia intestinalis, 

and one (3.0%) caused by both Cryptosporidium and Giardia 

(Tables 2–7; Figure 5). Of the 13 gastroenteritis outbreaks 

associated with untreated water venues, only two (15.4%) were 

caused by parasites. Two cryptosporidiosis outbreaks occurred; 

one in an untreated lake and the other in an untreated pond, 

causing 27 and six cases of illness, respectively. In contrast, 

parasites were the most common causes of gastroenteritis outbreaks associated with treated water venues; Cryptosporidium 

was the most common parasitic agent, causing 29 (82.9%) of 

the 35 outbreaks of gastroenteritis. Thirty-one of these parasitic gastroenteritis outbreaks occurred in treated water venues, causing illness in 3,784 persons. Three of these outbreaks 

each caused over 100 (range: 116–2,307 persons) cases of illness. In June 2005, an outbreak caused by C. hominis transmitted through a New York spray park resulted in 2,307 cases, 

mostly among young children. In August 2005, a C. hominis 

outbreak spread through multiple Ohio pools and resulted 
Vol. 57 / SS-9 Surveillance Summaries 9 

in 523 cases; this outbreak subsequently was linked to an 

outbreak in an adjoining state (Kentucky). In June 2006, an 

outbreak caused by Cryptosporidium at a water park in 

Missouri caused gastroenteritis in 116 persons 

The one additional parasitic outbreak was caused by 

Naegleria fowleri and led to the death of two persons in Oklahoma. Despite an investigation by local public health authorities, the location of suspected common exposure (i.e., exposure 

in which the two persons probably became ill at the same 

time and place) was not identified. 

Bacteria 

Eight reported gastroenteritis outbreaks of confirmed bacterial origin were reported (Figure 5), two of which were at 

treated water venues. An outbreak of Campylobacter jejuni 

occurred in a fill-and-drain pool at a Wyoming home in July 

2005, resulting in five children and one adult becoming ill. 

This same type of pool was the setting for a Shigella sonnei 

outbreak at a California home in July 2006, leading to nine 

persons becoming ill, including three 

who were hospitalized. Both of these 

outbreaks were caused by a lack of disinfection and heavy use of these pools
 

by young diaper-aged children. The 

other six outbreaks of gastroenteritis,
 

caused by bacteria, were associated with 

swimming in lakes, including three 

additional shigellosis outbreaks and 

three outbreaks of E. coli O157:H7 

infection. All six lake-associated outbreaks occurred during June and July and 

five were associated with exposure to lake
 

water during holidays or weekends.
 

Four of the bacterial outbreaks 

involved 28 cases of dermatitis caused 

by Pseudomonas aeruginosa; one of these 

outbreaks also resulted in ear infections. 

All four outbreaks of Pseudomonas 

infection occurred at treated water venues that involved heated spa water 

(some of these outbreaks also involved 

pools). Five additional outbreaks were 

suspected to have been caused by 

Pseudomonas on the basis of the clinical 

symptoms and exposure to a spa. 

Eight outbreaks caused by Legionella 

were associated with treated recreational 

water venues during 2005–2006, causing 

124 cases of legionellosis (i.e., LD and PF) 

and resulted in three deaths. The largest 

FIGURE 2. Number of recreational water-associated outbreaks 

(n = 78) — United States, 2005–2006*

>4 (six states) 

3 (three states) 

2 (nine states) 

1 (13 states) 

0 (19 states) 

* Note: These numbers are largely dependent on reporting and

surveillance activities in individual states and do not necessarily indicate 

the true incidence in a given state.

FIGURE 3. Recreational water-associated outbreaks, by type of exposure, type of

etiologic agent, predominant illness, and route of entry — United States, 2005–2006 

Type of exposure (n = 78) Type of etiologic agent (n = 78)
 

Treated water Parasitic 

74.4% 43.6%

Viral 5.1% 

Bacterial- Chemical/Toxin Legionella 10.3% 2.6% 

Untreated Bacterial- Unidentified water non-Legionella 17.9% 25.6% 20.5%
 

Predominant illness (n = 78)* Route of entry (n = 78) 

AGI Ingestion

61.5% 61.5%

Other† 

Mixed 6.4% 3.8% 

Combined Neuro 1.3% 

3.8% Leptospirosis 2.6% Inhalation ARI Skin 14.1% 14.1% 14.1% 

Contact 

15.4% 

* AGI: acute gastrointestinal illness; ARI: acute respiratory illness; Skin: illness, condition or symptom

related to skin; Mixed: a combination of illnesses, conditions, or symptoms that might also include 

the eyes and ears; and Neuro: neurologic condition or symptoms (e.g., meningitis). 

† Infection with Naegleria was categorized as other because of the nasal, noninhalational route of

infection. Infection with Leptospira was categorized as other because the route of infection is 

typically through contact with mucous membrane or broken or abraded skin. 
10 MMWR September 12, 2008 

TABLE 6. Number of waterborne-disease outbreaks (n = 78) associated with recreational water, by predominant illness and type 

of water — United States, 2005–2006 

Type of water 

Treated Untreated Total 

No. of No. of No. of No. of No. of No. of 

Predominant illness outbreaks cases outbreaks cases outbreaks (%) cases (%) 

AGI 35 3,849 13 166 48 (61.5) 4,015 (91.0) 

ARI 10 152 1 3 11 (14.1) 155 (3.5) 

Ear and Skin 1 7 0 0 1 (1.3) 7 (0.2) 

Ear and ARI 1 12 0 0 1 (1.3) 12 (0.3) 

Eye and ARI 2 44 0 0 2 (2.6) 44 (1.0) 

Leptospirosis 0 0 2 46 2 (2.6) 46 (1.0) 

Neuro 0 0 1 2 1 (1.3) 2 (0.0) 

Skin 9 103 2 4 11 (14.1) 107 (2.4) 

Other 0 0 1 24 1 (1.3) 24 (0.5) 

Total (%) 58 (74.4) 4,167 (94.4) 20 (25.6) 245 (5.6) 78 (100.0) 4,412 (100.0) 

* AGI: acute gastrointestinal illness; ARI: acute respiratory illness; Ear: illness, condition, or symptom related to ears; Skin: illness, condition, or symptom 

related to skin; Eye: illness, condition, or symptom related to eyes;. Neuro: neurologic condition or symptoms (e.g. meningitis); and Other: etiology 

unidentified. Whereas certain swimmers had symptoms consistent with seabathers eruption (caused by jellyfish larvae), the majority of persons affected 

in this outbreak experienced systemic, flu-like illnesses which might have been related to another etiology. Swimmers alternated between marine and 

chlorinated swimming venues. 

FIGURE 4. Number of recreational water-associated outbreaks 

(n = 78), by predominant illness* and month — United States, 

2005–2006 

25 

20 

15 

10 

5 

0 

Leptospirosis 

Mixed 

Neuro 

ARI 

Skin 

AGI 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Month 

* Mixed: a combination of illnesses, conditions or symptoms that also 

might include the eyes and ears; Neuro: neurologic condition or 

symptoms (e.g., meningitis); ARI: acute respiratory illness; Skin: illness, 

condition, or symptom related to skin; AGI: acute gastrointestinal illness. 

of these outbreaks was linked to a spa at an Illinois hotel and 

involved 43 persons, including three cases of LD resulting in 

one death. The environmental investigation documented 

inadequate disinfection in the spa and isolated both 

L. pneumophila and L. maceachernii from the spa water. 

Two outbreaks in untreated recreational water were caused 

by Leptospira. Leptospirosis was diagnosed in 43 persons who 

participated in an adventure race in Florida in November 2005. 

A July 2005 outbreak of leptospirosis in California involved 

three persons who had contact with water from a low flowing 

stream at the time of exposure 

Viruses

Four outbreaks of confirmed viral origin occurred, all of 

which caused gastroenteritis. Norovirus was identified as the 

etiologic agent in each of the outbreaks; three occurred at lake 

swimming beaches, and one occurred in a treated water setting. These four norovirus outbreaks resulted in 86 cases of 

gastroenteritis. For the two outbreaks where lake water fecal 

indicator testing was conducted; no water quality-violations 

were documented. The water might have been contaminated 

by ill swimmers at the time of exposure rather than by ongoing point source water contamination. The treated venue outbreak occurred in a hotel pool and was related to inadequate 

disinfection and continued use by ill swimmers. One additional outbreak that was suspected to have been caused by 

norovirus resulted in 13 cases. 

Chemicals

During 2005–2006, two outbreaks associated with chemicals involved 22 persons. In June 2005, a chemical-associated 

outbreak occurred in a Michigan lake causing respiratory 

symptoms in three swimmers. This outbreak was attributed 

to the unapproved addition of excessive amounts of copper 

sulfate to the lake water for aquatic nuisance control. 

The other outbreak occurred in a treated water venue. In 

July 2005, the recirculation pump at a community pool was 

shut down for maintenance; however, the liquid chlorine (i.e., 

NaOCl) and muriatic (i.e., hydrochloric) acid continued to 

feed into the system and probably released chlorine gas in the 

piping. When the pump was restarted, a concentrated bolus 

of these swimming pool chemicals and chlorine gas was sent 

into a small pool where it caused respiratory distress in 19 
TABLE 7. Number of waterborne-disease outbreaks (n = 78) associated with recreational water, by etiologic agent(s) and type of 

water — United States, 2005–2006 

Type of water 

Treated Untreated Total 

Predominant illness 

No. of 

outbreaks 

No. of No. of 

cases outbreaks 

No. of 

cases 

No. of 

outbreaks (%) 

No. of 

cases (%) 

Bacteria 14 

Campylobacter jejuni 1 

Escherichia coli spp. 0 

Leptospira spp. 0 

Legionella spp.* 8 

Pseudomonas aeruginosa 4 

Shigella sonnei 1 

Parasites 31 

Cryptosporidium spp. 29 

Giardia intestinalis 1 

Naegleria fowleri 0 

Cryptosporidium and Giardia spp.† 1 

Viruses 1 

Norovirus 1 

Chemicals/toxins 1 

Copper sulfate 0 

Chlorine gas§ 1 

Suspected etiology 9 

Suspected chemical exposure¶ 1 

Suspected chloramines 3 

Suspected norovirus 0 

Suspected P. aeruginosa 5 

Suspected schistosomes 0 

Unidentified 2 

Total (%) 58 (74.4) 

167 

6 

0 

0 

124 

28 

9 

3,784 

3,718 

11 

0 

55 

18 

18 

19 

0 

19 

135 

9 

53 

0 

73 

0 

44 

4,167 (94.4) 

8 

0 

3 

2 

0 

0 

3 

3 

2 

0 

1 

0 

3 

3 

1 

1 

0 

3 

0 

0 

1 

0 

2 

2 

20 (25.6) 

88 

0 

10 

46 

0 

0 

32 

35 

33 

0 

2 

0 

68 

68 

3 

3 

0 

17 

0 

0 

13 

0 

4 

34 

245 (5.6) 

22 (28.2) 

1 

3 

2 

8 

4 

4 

34 (43.6) 

31 

1 

1 

1 

4 (5.1) 

4 

2 (2.6) 

1 

1 

12 (15.4) 

1 

3 

1 

5 

2 

4 (5.1) 

78 (100.0) 

255 (5.8) 

6 

10

46

124 

28

41

3,819 (86.6) 

3,751 

11

2 

55

86 (1.9) 

86

22 (0.5) 

3 

19

152 (3.4) 

9 

53

13

73

4 

78 (1.8) 

4,412 (100.0) 

Vol. 57 / SS-9 Surveillance Summaries 11 

* Five outbreaks were attributed to Legionella pneumophila, two outbreak investigations did not identify a Legionella species, and one outbreak investigation 

detected L. pneumophila and L. maceachernii in both pool and spa water. 

†Thirty-five persons had stool specimens that tested positive for Giardia, seven persons had stool specimens that tested positive for Cryptosporidium, 

and two persons had stool specimens that tested positive for both Giardia and Cryptosporidium. §Chlorine gas was released after high levels of liquid chlorine and acid were mixed in the recirculation system and subsequently released into the pool 

water. 

¶Low pH suspected on the basis of water testing and symptoms. 

persons. Three additional outbreaks in treated venues were 

suspected of being caused by disinfection by-products (e.g., 

chloramines) on the basis of symptoms and settings (i.e., 

indoor pool). 

Suspected Agents 

Twelve outbreaks were reported in which no etiologic agent 

was confirmed; however, investigation reports indicated a suspected agent on the basis of symptoms, type of water, setting, 

and background information (Table 7). Five of these 12 outbreaks were suspected to be caused by P. aeruginosa in treated 

spas. One outbreak, which caused rashes in nine children, was 

suspected of being caused by low pH. Three chemical-related 

outbreaks were suspected to be associated with exposure to 

excess chloramines (i.e., disinfection by-products of chlorination) (20–22) in the indoor pools and surrounding areas (i.e., 

indoor pool air), which resulted in ARI, and eye irritation. 

Norovirus was the suspected pathogen in one gastroenteritis 

outbreak associated with a lake on the basis of epidemiologic and 

clinical evidence. Two outbreaks were suspected to be the result 

of contact with avian schistosomes, causing cercarial dermatitis 

Unidentified Etiologic Agents 

Data collected during investigations of four outbreaks of 

unidentified etiology were not sufficient to suggest an etiologic agent. Gastroenteritis was reported as the predominant 

illness in two of these outbreaks, and ARI and ear infections 

were reported for the third one. The AGI outbreak in a treated 

venue (Minnesota 2005) caused illness in 32 persons over the 

course of nearly a month; 15 persons reportedly continued to 

swim while ill. Stool samples tested negative for bacteria, 

viruses, and parasites. A lake-associated AGI outbreak sickened 10 persons and caused five hospitalizations. Environmental testing revealed water-quality violations (e.g., elevated 

E. coli levels). An outbreak of ARI and ear infections among 

lifeguards occurred in a pool that had not officially opened 

for the season. The water was reportedly cloudy and possibly 

contaminated by water leaking from a pipe in the facility. 
12 MMWR September 12, 2008 

Finally, an outbreak of influenza-like illness linked to an ocean 

beach was associated with marine and pool water; possible 

etiologies might include contact with jellyfish larvae and other 

etiologies may have contributed to some of these illnesses. 

Single Cases of Waterborne Disease 

Vibriosis Cases Associated with Recreational 

Water 

During 2005–2006, a total of 189 vibriosis cases associated 

with recreational water use or exposure to flood water were 

reported from 20 states; representing 14.7% (189/1287) of 

the total number of vibriosis cases reported in 2005–2006 

(62). Eighty-five (45.0%) of 189 patients were hospitalized, 

and 18 (9.5%) died (Table 8). 

The most frequently isolated Vibrio species was Vibrio 

vulnificus, which was isolated from 67 (35.4%) persons; 

52 (77.6%) were hospitalized, and 15 (22.4%) died. 

V. alginolyticus was isolated from 60 (31.7%) persons; seven 

(11.7%) were hospitalized, and none died. V. parahaemolyticus 

was isolated from 33 (17.5%) persons; 12 (36.4%) were 

hospitalized, and one (3.0%) died. Other Vibrio species 

(including V. cholerae non-O1, non-O139, V. damsela, V. fluvialis, 

V. hollisae, V. mimicus, V. alginolyticus/parahaemolyticus coinfection, V. alginolyticus/fluvialis coinfection, V. parahaemolyticus/ 

vulnificus coinfection, V. vulnificus/unidentified Vibrio species 

coinfection and Vibrio species not identified) were identified in 

FIGURE 5. Recreational water-associated outbreaks of gastroenteritis, by type of 

exposure and etiologic agent — United States, 2005–2006 

Etiologic agent: untreated water (n = 13) Etiologic agent: treated water (n = 35)* 

S. sonnei 

23.1% 

Norovirus 

23.1% 

E. coli 

O157:H7 

23.1% 

Unidentified 

15.4% 

Cryptosporidium 

spp. 82.8% 

Etiologic agent (n = 48) 

Cryptosporidium spp. 

64.6% Escherichia coli O157:H7 6.3% 

Type of exposure (n = 48)* 

Untreated water 

27.1% 

Treated water 

72.9% 

Campylobacter spp. 2.9% 

2.9% 

9 

9 

Norovirus 2.9% 

Unidentified 

2.9% 

2. % 

and spp. 2. % 

S. sonnei 

G. intestinalis 

Cryptosporidium Giardia 

Cryptosporidium spp. 

15.4% 

Campylobacter spp. 2.1% 

Cryptosporidium Giardia and spp. 2.1% 

Unidentified 6.3% 

Norovirus 8.3% 

G. intestinalis 2.1% 

Shigella sonnei 8.5% 

* For one outbreak (Wyoming 2006) case-patients reported exposure to multiple community pools 

and to a reservoir. This outbreak is being analyzed as exposure to treated water. 

29 (15.3%) persons; 14 (48.3%) were hospitalized, and two 

(6.9%) died. 

Geographic location. Nearly all Vibrio patients reported 

that they were exposed to recreational water in a coastal state 

(Figure 6). The most frequently reported location was the Gulf 

Coast (61.9%); Atlantic Coast states, excluding Florida 

(19.6%); Pacific Coast states (16.9%); and inland states (1.6%) 

(Table 9). Florida and Mississippi reported the highest number of cases, 55 and 28 cases, respectively (Figure 6; Table 9). 

Seasonality. The temporal distribution of illness in patients 

from whom Vibrio species were isolated displayed a clear 

seasonal peak during the summer (Figure 7). The greatest 

frequency of Vibrio cases occurred during July through 

September. 

Exposures. Activities associated with Vibrio cases included 

swimming, diving, or wading in water (70.9%); walking or 

falling on the shore or rocks (32.8%); and boating, skiing, or 

surfing (19.6%). Twenty-five case-patients reported exposure 

to Hurricane Katrina flood waters. 

Signs/Symptoms. Symptoms associated with Vibrio illnesses 

included cellulitis (56.6%), fever (36.0%), muscle pain 

(21.2%), bullae (15.9%), ear infections (14.3%), nausea 

(13.8%), and shock (10.1%). V. vulnificus accounted for the 

majority of skin infections (e.g., cellulitis, bullae), causing 70 

(50.7%) of 138. V. vulnificus also accounted for the majority 

of severe illnesses, including those with fever (51.5%), bacteremia (75.0%), shock (73.7%), and amputations (83.3%). 

V. alginolyticus accounted for the 

majority of ear infections (24 [92.3%] 

of 26). Other symptoms and infections 

were reported in low frequencies (e.g., 

bladder infections, hematuria, eye 

infections, respiratory symptoms, sinus 

infections, diarrhea, and vomiting). 

Naegleria Infections 

In addition to the outbreak of PAM 

(two cases), three individual fatal cases 

of PAM caused by N. fowleri were 

reported in 2005–2006 (Table 10). 

A child in Texas died in September 

2005, 13 days after swimming in a lake. 

In August 2006, a child died of PAM 

associated with N. fowleri after swimming, using a personal watercraft, and 

tubing in an Arizona lake. In August 

2006, a child died after swimming in a 

Georgia pond. 
TABLE 8. Number of illnesses associated with Vibrio isolation (n = 189) and recreational water, by species and year — United 

States, 2005–2006 

Year 

2005 2006 Total 

Species Cases Hospitalizations Deaths Cases Hospitalizations Deaths Cases Hospitalizations Deaths 

Vibrio alginolyticus 

V. cholerae non-O1, non-O139 

V. damsela 

V. fluvialis 

V. hollisae 

V. mimicus 

V. parahaemolyticus 

V. vulnificus 

Multiple* 

Vibrio, species not identified 

Total (% of cases) 

 Percentage by year 

31 

4 

2 

2 

1 

0 

21 

50 

3 

4 

118 

(62.4) 

6 

2 

0 

2 

0 

0 

8 

41 

3 

3 

65 (55.1%) 

(76.5) 

0 

0 

0 

1 

0 

0 

1 

11 

1 

0 

14 (11.9%) 

(77.8) 

29 

4 

0 

1 

0 

1 

12 

17 

2 

5 

71 

(37.6) 

1 

1 

0 

0 

0 

0 

4 

11 

1 

2 

20 (28.2%) 

(23.5) 

0 

0 

0 

0 

0 

0 

0 

4 

0 

0 

4 (5.6%) 

(22.2) 

60 

8 

2 

3 

1 

1 

33 

67 

5 

9 

189 

(100) 

7 0 

3 0 

0 0 

2 1 

0 0 

0 0 

12 1 

52 15 

4 1 

5 0 

85 (45.0%) 18 (9.5%)

(100) (100) 

Vol. 57 / SS-9 Surveillance Summaries 13 

* Includes V. alginolyticus/parahaemolyticus coinfection, V. alginolyticus/fluvialis coinfection, V. parahaemolyticus/vulnificus coinfection, V. vulnificus/ 

unidentified, and Vibrio species coinfection. 

Previously Unreported Outbreaks 

Thirty-one previously unreported recreational water-associated 

outbreaks and one case of waterborne disease during 1978– 

2004 were received and entered into WBDO database 

(Table 11). These outbreaks were summarized but not included 

in analysis for this report. One outbreak of leptospirosis in 

Hawaii was associated with exposure to flood water (48). 

Reports on the remaining 30 events were received from Minnesota, New York, and Tennessee. These states participate in 

the Environmental Health Specialist Network Water program 

(EHS-Net Water), which is an EPA and CDC funded initiative that supports a waterborne-disease environmental health 

specialist in each site. These three sites identified outbreaks 

and case reports that were previously unreported to CDC and 

reported them as part of a retrospective review of waterborne 

disease outbreaks in these states. The 31 previously unreported 

outbreaks affected 673 persons; 25 (80.6%) of the outbreaks 

occurred in treated water venues. 

Surveillance Reports Not Classified 

as Waterborne Disease and Outbreaks 

One report from New Hampshire was not included in this 

summary. In February 2005, three children had lesions 

believed to be caused by Molluscum contagiosum. These children all swam at the same community pool; however, after 

investigation, it was not clear that these lesions were associated with waterborne transmission of this organism versus 

other modes of transmission (e.g., person to person or contact with contaminated towels or objects). 

FIGURE 6. Number* of illnesses associated with Vibrio isolation 

and recreational water (n = 189) — United States, 2005–2006 

>10 (six states) 

5–9 (four states) 

2–4 (five states) 

1 (five states) 

0 (30 states) 

* Note: These numbers are largely dependent on reporting and 

surveillance activities in individual states and do not necessarily indicate 

the true incidence in a given state. 

Aquatic Facility-related Health Events 

not Associated with Recreational Water 

Thirty-two reports of nonwater related health events that 

occurred during 1983–2006 and were associated with aquatic 

facilities were reported by New York (Table 12). Although 

they are not counted as waterborne-disease cases or outbreaks 

for analysis purposes, they are included in this report because 

they illustrate important lessons about pool maintenance and 

operation. Most of these events, 90.6% (29/32), were caused 

by improper use of chemicals; incompatible pool chemicals 

(e.g., acid and bleach) were mixed, which resulted in the 

release of chlorine gas. Persons at these aquatic facilities expe­
14 MMWR September 12, 2008 

TABLE 9. Number of recreational water-associated Vibrio isolations (n = 189) and deaths (n = 18), by region/state and species — 

United States, 2005–2006 

Species 

V. alginolyticus V. parahaemolyticus V. vulnificus Other/unknown species* Total 

Region/State† Cases Deaths Cases Deaths Cases Deaths Cases Deaths Cases Deaths 

Atlantic 

Connecticut 

Georgia 

Maine 

Maryland 

North Carolina 

New Jersey 

New York 

South Carolina 

Virginia 

Total 

Gulf Coast§ 

Alabama 

Florida¶ 

Louisiana 

Mississippi 

Texas 

Total 

Noncoastal 

Illinois 

Kansas 

Minnesota 

Total 

Pacific 

California 

Hawaii 

Oregon 

Total 

Total 

Percentage 

1 

0 

2 

2 

2 

1 

1 

3 

2 

14 

0 

19 

1 

0 

3 

23 

0 

0 

0 

0 

7 

15 

1 

23 

60 

(31.7) 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

(0) 

2 

0 

0 

2 

2 

4 

0 

0 

2 

12 

1 

9 

0 

6 

4 

20 

0 

0 

0 

0 

0 

1 

0 

1 

33 

(17.5) 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1 

0 

1 

0 

0 

0 

0 

0 

0 

0 

0 

1 

(5.6) 

0 

1 

0 

2 

3 

0 

0 

0 

0 

6 

0 

16 

19 

18 

3 

56 

0 

0 

0 

0 

1 

4 

0 

5 

67 

(35.4) 

0 

0 

0 

0 

1 

0 

0 

0 

0 

1 

0 

1 

5 

6 

0 

12 

0 

0 

0 

0 

0 

2 

0 

2 

15 

(83.3) 

0 

0 

0 

0 

1 

1 

1 

0 

2 

5 

1 

11 

1 

4 

1 

18 

1 

1 

1 

3 

2 

1 

0 

3 

29 

(15.3) 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1 

0 

1 

0 

2 

0 

0 

0 

0 

0 

0 

0 

0 

2 

(11.1) 

3 

1 

2 

6 

8 

6 

2 

3 

6 

37 

2 

55 

21 

28 

11 

117 

1 

1 

1 

3 

10 

21 

1 

32 

189 

(100) 

0 

0 

0 

0 

1 

0 

0 

0 

0 

1 

0 

2 

5 

8 

0 

15 

0 

0 

0 

0 

0 

2 

0 

2 

18 

(100) 

* Includes V. cholerae (non-O1, non-O139), V. damsela, V. fluvialis, V. hollisae, V. mimicus, V. alginolyticus/parahaemolyticus coinfection, V. alginolyticus/ 

fluvialis coinfection, V. parahaemolyticus/vulnificus coinfection, V. vulnificus/unidentified Vibrio species coinfection, and Vibrio species not identified. 

†Refers to the reported state of exposure if the exposure did not occur in the reporting state. 

§ Includes 25 cases with reported exposure to Hurricane Katrina flood waters. 

¶Nine reports from Florida indicate Atlantic coast exposure. 

rienced respiratory distress. Two additional events were caused 

by carbon monoxide in indoor pools, and one event was caused 

by liquid chlorine splashing into the eye of an aquatic facility 

employee. 

Discussion 

Trends in Reporting Outbreaks 

A total of 78 recreational water–associated WBDOs were 

reported to CDC during 2005–2006. This represents an 

increase from the 2003–2004 Surveillance Summary (n = 62) 

and is the largest number of outbreaks ever reported in a 

2-year period (Figure 8). Overall, the number of reported recreational water-associated WBDOs reported annually have 

increased substantially since 1978, when CDC first began 

receiving these reports (Figure 8). These increases probably 

are a result of a combination of factors, such as the emergence 

of pathogens (e.g., Cryptosporidium), increased participation 

in aquatic activities, and increases in the number of aquatic 

venues. Increased recognition, investigation, and reporting of 

recreational water-associated outbreaks also might be contributing factors. 

An unprecedented number of states reported outbreaks 

during 2005–2006, and WBDOs demonstrate geographic 

variation (Figure 2). Differences in reporting between states 

might be attributable to several factors, including ability to 

detect outbreaks, availability of laboratory testing, variable 

requirements for notifiable diseases, and the surveillance and 

investigation capacity of individual state and local public health 
Vol. 57 / SS-9 Surveillance Summaries 15 

FIGURE 7. Number of illnesses associated with Vibrio isolation 

and recreational water (n = 189), by species and month — 

United States, 2005–2006 

50 

Other species* (n = 29) 

40 V. parahaemolyticus (n = 33)

V. alginolyticus (n = 60) 

V. vulnificus (n = 67) 30 

20 

10 

0 

Month 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

* Includes V. cholerae (non-O1, non-O139) (eight), V. damsela (two), 

V. fluvialis (three), V. hollisae (one), V. mimicus (one), V. alginolyticus/ 

parahaemolyticus coinfection (one), V. alginolyticus/fluvialis coinfection 

(one), V. parahaemolyticus/vulnificus coinfection (two), V. vulnificus/ 

unidentified Vibrio species coinfection (one), and Vibrio species not 

identified (nine). 

agencies. These differences in the ability to detect, investigate, 

and report WBDOs probably lead to reporting and surveillance bias. Therefore, the states with the majority of outbreaks 

reported for this period might not be the states in which the 

majority of outbreaks actually occurred. An increase or 

decrease in the number of WBDOs reported might reflect 

either an actual change in the incidence of outbreaks or a 

change in the sensitivity of surveillance systems. 

Etiologic agents with shorter incubation periods might be 

more easily linked to water exposures, facilitating the recognition of outbreaks. Additional factors that might influence 

which WBDOs are reported include the size and location of 

the outbreak, severity of illness, and the geographic dispersion of ill persons. Larger outbreaks are more likely to be identified by public health authorities. In contrast, smaller 

outbreaks (e.g., those associated with private residential pools 

and spas) might go undetected because fewer persons are ill, 

and they might attribute illness to other common exposures. 

In addition, outbreaks of gastroenteritis associated with large 

venues that draw from a wide geographic range (e.g., large 

lakes and marine beaches) might be difficult to detect because 

potentially infected persons disperse widely from the site of 

exposure and, therefore, might be less likely to be identified as 

part of an outbreak. Prospective epidemiology studies, such 

as the EPA’s NEEAR Water Study (18), have revealed elevated 

rates of gastroenteritis in swimmers compared with nonswimmers on all beaches studied. Multiple other prospective studies of gastroenteritis associated with beach swimming have 

also indicated elevated rates of illness associated with swimming in lakes and oceans, though few outbreaks have been 

detected (23,24). Consistent with this finding, no oceanassociated outbreaks and only one Great Lakes-associated outbreak of gastroenteritis has been reported since 1978 (12). These 

endemic recreational water-associated illnesses are not captured 

by WBDOSS, supporting the need for more studies to estimate the magnitude of risk for illness for routine, nonoutbreakassociated exposures at recreational water venues. 

WBDOs associated with recreational water use occur yearround, but the numbers of reported WBDOs and cases are 

highest during the annual summer swim season (Figure 4). 

For public health professionals and swimming venue operators, the seasonality of waterborne-disease outbreaks can help 

determine the allocation of resources so that health education 

messages are targeted to populations during times of the year 

when the risk for preventable illness is highest. 

Swimming Pools 

Swimming pools are designed to be chemically treated and 

filtered to reduce the risk for illness associated with exposure 

to infectious pathogens. Despite the availability of these 

disinfection measures, pools remain susceptible to contamination because of chlorine-resistant organisms (i.e., 

Cryptosporidium) or inadequate treatment resulting from poor 

operation or maintenance. In addition, an emerging focus of 

concern at swimming pools is the risk for chemical injury 

from improper handling of pool chemicals. 

Infectious Gastroenteritis 

Approximately 87% of all cases reported to WBDOSS 

during 2005–2006 were involved in infectious gastroenteritis 

outbreaks associated with treated recreational water venues. 

TABLE 10. Single cases of non-Vibrio* waterborne disease (n = 3) associated with untreated recreational water, by state — 

United States, 2005–2006 

Predominant No. of cases 

State Date Etiologic agent illness† (deaths) (n = 3 ) Type Setting 

Arizona Aug 2006 Naegleria fowleri Neuro 1 (1) Lake Lake 

Georgia Aug 2006 N. fowleri Neuro 1 (1) Pond Pond 

Texas Sep 2005 N. fowleri Neuro 1 (1) Lake Lake 

* In addition to these single cases, 189 cases of recreational water-associated Vibrio infection were reported: 118 cases in 2005 and 71 cases in 2006. 

†Neuro: neurologic condition or symptoms (e.g., meningitis). 
TABLE 11. Waterborne disease (n = 1) and outbreaks (n = 31) associated with recreational water that were not included in 

previous Surveillance Summaries, by state — United States, 1978–2004 

Predominant No. of cases 

State Date Class* Etiologic agent illness † (n = 673) Type Setting 

Disease 

New York Jul 1992 NA Unidentified§ Eye 1 Pool Hotel 

Outbreak 

Hawaii Nov 2004 IV Leptospira interrogans¶ Lep 2 Stream University 

Minnesota Jul 1992 III Unidentified** Skin 6 Pool Hotel 

Minnesota Jan 1998 III Giardia intestinalis AGI 7 Pool Hotel 

Minnesota Apr 1998 II Unidentified** Ear, eye, skin 17 Pool Community 

Minnesota May 1998 III Unidentified** Skin 22 Pool Community 

Minnesota Jul 1998 IV Norovirus†† AGI 15 Lake Swimming beach 

Minnesota Jul 2000 I Legionella§§ ARI 51 Pool, spa Hotel 

New York Oct 1978 IV P. aeruginosa Skin 2 Spa Hotel 

New York Aug 1981 IV Leptospira Lep 6 Stream Swimming area 

New York Aug 1988 III Chlorine gas¶¶ AGI, ARI 21 Pool Community 

New York Mar 1989 III Unidentified§ ARI, skin 3 Pool Hotel 

New York Jul 1989 III Chlorine gas¶¶ ARI 11 Pool College 

New York Jun 1990 III Chlorine gas¶¶ ARI 15 Pool School 

New York Mar 1992 III P. aeruginosa Skin 34 Spa Resort 

New York May 1992 III P. aeruginosa Skin 6 Pool, spa Hotel 

New York Oct 1992 III Unidentified*** Eye, skin, other 20 Pool School 

New York Nov 1994 III Unidentified§ AGI, ARI, eye, skin 51 Pool School 

New York Mar 1995 III Chlorine gas¶¶ ARI 5 Pool Membership club 

New York Nov 1995 III P. aeruginosa Skin 13 Pool Hotel 

New York Dec 1995 III P. aeruginosa Skin 3 Pool School 

New York Jan 1996 IV Unidentified††† ARI, skin 29 Pool, spa Hotel 

New York Mar 1997 III P. aeruginosa Skin 10 Pool Hotel 

New York Mar 1997 IV Unidentified** Skin 19 Pool Hotel 

New York Sep 1997 III Chloramines ARI, eye, skin 51 Pool School 

New York Sep 1998 III Hydrochloric acid ARI 3 Pool School 

New York Jan 1999 III Unidentified§ Eye, skin 2 Pool School 

New York Jun 1999 III Unidentified§§§ AGI 140 Lake Swimming beach 

New York Mar 2000 III Unidentified§ Eye 2 Pool Hotel 

New York Feb 2001 I Chlorine¶¶¶ Skin 58 Pool, spa Hotel 

New York Jul 2002 III Shigella sonnei AGI 20 Lake Swimming beach 

Tennessee Jun 1997 II Cryptosporidium AGI 28 Lake Swimming beach 

16 MMWR September 12, 2008 

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12 (available at http://www.cdc.gov/healthyswimming/downloads/ 

cdc_5212_waterborne.pdf). NA: Single cases of waterborne disease are not classified (see Table 1). 

† Eye: illness, condition, or symptom related to eyes; Lep: leptospirosis; Skin: illness, condition, or symptom related to skin; AGI: acute gastrointestinal 

illness; Ear: illness, condition, or symptom related to ears; ARI: acute respiratory illness; and Other: undefined illness, condition, or symptom. 

§ Etiology unidentified: chemical contamination from excess chlorine levels or pool disinfection by-products (e.g., chloramines) suspected. 

¶ Source: Gaynor K, Katz AR, Park SY, Nakata M, Clark TA, Effler PV. Leptospirosis on Oahu: an outbreak associated with flooding of a university 

campus. Am J Trop Med Hyg 2007;76:882–5. 

** Etiology unidentified: P. aeruginosa suspected on the basis of clinical syndrome and setting. 

†† Four persons had stool specimens that tested positive for norovirus, and three persons had stool specimens that tested positive for Staphylococcus aureus.
 §§ All cases were diagnosed as Pontiac fever (PF).
 

¶¶ Chlorine gas was released after high levels of liquid chlorine and acid were mixed in the recirculation system and subsequently released into the pool
 

water. 

*** Etiology unidentified: high chlorine levels, disinfection by-products, and low pH suspected on the basis of clinical syndrome and setting. In addition to 

burning eyes and irritated skin, swimmers experienced teeth staining and loss of body hair. 

†††Etiology unidentified: Legionella and P. aeruginosa suspected on the basis of clinical syndrome (PF and rash) and setting.
 §§§Etiology unidentified: norovirus suspected on the basis of clinical syndrome.
 

¶¶¶ Injuries occurred after the hand-addition of chlorine into a pool while swimmers were using it.
 

Two outbreaks were caused by chlorine-sensitive agents no documented response existed that indicated that chlorine 

(Giardia in Massachusetts, July 2005, and norovirus in was added or that the pool was closed. Previous outbreak 

Wisconsin, May 2006) and might have been prevented or investigations have demonstrated that the implementation of 

reduced in scale by proper aquatic monitoring, maintenance, appropriate pool operation practices (e.g., adequate disinfecand/or operation practices. Investigation of the Massachusetts tion) effectively stops the transmission of chlorine-sensitive 

giardiasis outbreak revealed that although the chlorine levels pathogens (25). 

recorded on the pool log were below the recommended level, 
TABLE 12. Other aquatic facility-related health events* (n = 32) not associated with recreational water use — New York, 1983–2006 

Predominant No. of cases 

State Date Etiologic agent illness† (n = 364 ) Type Setting 

New York Mar 1983 Chlorine gas§ ARI 3 Pool Housing complex 

New York Aug 1983 Chlorine gas§ ARI 1 Pool Housing complex 

New York May 1984 Chlorine gas¶ ARI 8 Pool College 

New York Jun 1987 Chlorine gas§ ARI 6 Pool Community 

New York Aug 1987 Chlorine gas§ ARI 41 Pool Membership club 

New York Aug 1988 Chlorine gas§ ARI 10 Pool Membership club 

New York Oct 1988 Chlorine gas§ ARI 1 Pool School 

New York Dec 1988 Chlorine gas§ ARI, eye 29 Pool Institution 

New York Feb 1989 Chlorine gas§ ARI 6 Pool School 

New York Jul 1989 Chlorine gas¶ ARI 1 Pool Community 

New York Jul 1989 Chlorine gas§ ARI 1 Pool Hotel 

New York Jul 1991 Chlorine gas§ ARI 5 Pool School 

New York Jan 1992 Chlorine gas§ ARI 2 Pool Membership club 

New York Jun 1992 Chlorine gas§ ARI, eye 2 Pool School 

New York Feb 1993 Carbon monoxide suspected AGI, ARI 18 Pool School 

New York Sep 1993 Chlorine gas§ ARI 3 Pool Membership club 

New York Jun 1994 Chlorine gas§ ARI 1 Pool Membership club 

New York Jun 1994 Chlorine gas§ ARI 1 Pool Institution 

New York Jun 1995 Chlorine gas§ ARI 48 Pool School 

New York Oct 1995 Chlorine gas§ ARI 91 Pool School 

New York Jul 1996 Chlorine gas§ ARI 1 Pool Membership club 

New York Apr 1997 Chlorine gas§ ARI 14 Pool School 

New York Jun 1997 Chlorine gas§ ARI 15 Pool Membership club 

New York Aug 1997 Chlorine gas§ ARI 18 Pool School 

New York Dec 1997 Chlorine gas§ ARI 17 Pool Membership club 

New York Jul 1998 Chlorine liquid Eye 1 Pool Hotel 

New York Feb 2000 Carbon monoxide ARI 4 Pool Hotel 

New York Jan 2001 Chlorine gas§ ARI 1 Pool School 

New York Jun 2002 Chlorine gas§ ARI 1 Pool Housing complex 

New York Apr 2005 Chlorine gas§ ARI 9 Pool Membership club 

New York Jul 2006 Chlorine gas§ ARI 1 Pool Community 

New York May 2006 Chlorine gas§ ARI 4 Pool Community 

Vol. 57 / SS-9 Surveillance Summaries 17 

* These events are not considered waterborne outbreaks because the vehicle of transmission was not water. 

†AGI: acute gastrointestinal illness; ARI: acute respiratory illness; and Eye: illness, condition or symptom related to eyes. 

§Chlorine gas was generated after inappropriate chemical preparation or mixing (e.g., liquid chlorine bleach and acid). 

¶Chlorine gas that was used to disinfect pool water was released, causing injury. 

During 2005–2006, Cryptosporidium spp. caused 31 recreational water–associated outbreaks, which involved 3,751 

persons; 99.1% of these cases were associated with treated water 

venues. The number of the cryptosporidiosis outbreaks 

reported annually has substantially increased from nine in 

1997–1998 to 31 in 2005–2006 (Table 7). This increase is 

particularly noticeable in the proportion of AGI outbreaks 

associated with Cryptosporidium in treated recreational water 

venues (Figures 5 and 9). These increases contribute to the 

observed increases in the total number of recreational water– 

associated outbreaks and, more specifically, outbreaks of gastroenteritis. Concurrently, cases of cryptosporidiosis reported 

to CDC have nearly doubled since 2004 (26). Although the 

reasons for increased cryptosporidiosis case and outbreak reporting are not completely understood, outbreaks associated 

with treated recreational water venues continue to be an important means of transmitting Cryptosporidium. 

During 1997–2006, Cryptosporidium was infrequently 

attributed to outbreaks associated with lakes and rivers (12.7% 

of outbreaks), although it caused 68.3% of outbreaks associated with treated venues (Figure 9). This observation is consistent with the finding that Cryptosporidium requires extended 

contact time with chlorine for inactivation; oocysts can survive for days in the chlorine levels that are typically recommended for swimming pools (1–3 ppm free chlorine; 27). 

The continued reporting of cryptosporidiosis outbreaks associated with the use of treated recreational water venues underscores the importance of other prevention measures that reach 

beyond conventional pool chlorination and filtration, which 

are the primary barriers to infectious disease transmission (28). 

WBDOs of cryptosporidiosis have stimulated the use of alternative treatment technologies and other potential risk-reduction steps to keep swimming venues safe. Ultraviolet light 

(29–31) and ozonation (27,32) disinfection effectively inac­
18 MMWR September 12, 2008 

FIGURE 8. Number of recreational water-associated outbreaks 

(n = 557),* by year and illness† — United States, 1978–2006 

45 

30 

15 

0 

Other 

ARI 

Skin 

AGI 

§ 

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 

Year 

* Single cases of primary amebic meningoencephalitis (n = 60) have been 

removed from this figure; therefore, it is not comparable to figures in 

previous Surveillance Summaries. 

†AGI: acute gastrointestinal illness; Skin: illness, condition, or symptom 

related to skin; ARI: acute respiratory illness; Other: includes keratitis, 

conjunctivitis, otitis, bronchitis, meningitis, meningoencephalitis, hepatitis, 

leptospirosis, and combined illnesses. 

§All outbreaks of legionellosis (i.e., Legionnaires’ disease and Pontiac fever) 

are classified as ARI. 

tivate Cryptosporidium and are available for use at aquatic venues. Other potential risk-reduction steps include increased circulation flow rates, flocculants, remedial biocidal shock 

treatments [i.e., routine hyperchlorination: 20 ppm free chlorine for 12.75 hours or the equivalent (31,33)], and occupancy-dependent water replacement. In addition, 

cryptosporidiosis outbreaks highlight the need for improved 

operator training and continued education of the general public concerning healthy swimming practices to reduce the risk 

for RWI. 

Because Cryptosporidium is resistant to the chlorine levels 

used in pools, outbreaks can occur, even in facilities that are 

well-maintained. Therefore, rapid public health response and 

increased community involvement are needed to prevent the 

expansion of these outbreaks (34). One cryptosporidiosis outbreak (Iowa, June 2005) that occurred in a community swimming pool demonstrates how a rapid community-wide public 

health response during the early stages of an outbreak can 

help control the potential spread of illness into the community. In Iowa, detection and investigation started 2 weeks 

after exposure. The response included mitigating actions (e.g., 

ordering hyperchlorination of the implicated pool and all pools 

within a 20-mile radius and then confirming compliance; 

containing the outbreak through collaborative efforts between 

epidemiologists and environmental health specialists; posting 

signs at the implicated pool’s entrance; instructing those with 

diarrhea not to enter the pool; and educating the public about 

good hygiene practices). The investigation indicated that no 

transmission had apparently occurred outside of the single 

implicated community pool, suggesting that these control 

measures might have prevented further spread. An interstate 

cryptosporidiosis outbreak (Kentucky, June 2005; and Ohio, 

August 2005) highlighted the need for additional intra-agency 

collaboration (e.g., between epidemiologists detecting cases 

and environmental health specialists permitting and inspecting pools) and communication between states. 

Modification of swimming behavior is a critical component 

in reducing recreational water-associated outbreaks. Swimming 

is essentially communal bathing, and continued swimming 

during diarrheal illness and the common occurrence of swallowing recreational water pose a public health challenge. 

Multiple findings underscore the relation between human 

behavior and disease transmission at recreational water venues. First, in multiple outbreaks, fecal accidents were observed 

at the implicated pools on the days when the outbreak exposures were thought to have occurred (Florida, August 2006; 

and Illinois, July 2006). Second, at least five outbreaks (New 

York, June 2005; Ohio, August 2005; Illinois, July 2006; 

Minnesota, September 2006; and South Carolina, July 2006) 

were caused by Cryptosporidium hominis, indicating a human 

source of water contamination. Third, swallowing water at 

the implicated recreational water venue was associated with 

illness in three outbreaks (Colorado, August 2006; Florida, 

June 2005; and New York, June 2005). All of these outbreaks 

highlight how recreational water can amplify transmission of 

fecal-oral pathogens. These findings underscore the need for 

public education about the importance of not swimming during diarrheal illness and not swallowing recreational water, 

and the importance of clarifying with the public that recreational water is neither drinking water nor sterile. Aquatic 

facilities should be diligent about informing patrons of these 

public health concerns and emphasizing that persons with 

diarrhea should not swim and all swimmers should practice 

good hygiene. These policies should apply to all patrons, particularly young children and visitors from high-risk settings 

(e.g., child care centers), which have diarrhea exclusion policies but might not enforce them routinely. They also should 

apply to all aquatics facility staff. Standardized policies for 

restricting staff who are ill with diarrhea from entering pools, 

similar to restricting ill foodhandlers from food preparation, 

should be established, implemented, and enforced (35). 

Finally, good hygiene is essential to ensure the cleanliness of 

swimmers entering pools. An adequate number of functioning, accessible hygiene facilities (i.e., toilets, diaperchanging areas, and showers) should be located near pools 

and should provide hot water and handwashing access to promote compliance. Documented fecal contamination of persons (36) suggests that swimmers should be encouraged to 

shower thoroughly (i.e., washing the peri-anal surface in par­
Vol. 57 / SS-9	 Surveillance Summaries 19 

ticular) before going to or entering the	 

pool. Diaper-changing facilities, with 

handwashing stations, should be 

located close to or at the poolside to 

encourage hygienic diaper-changing 

and handwashing. 

Chemical Toxicity 

During 2005–2006, pool chemicals 

or disinfection by-products were confirmed as the etiologic agent in one 

(Ohio, July 2005) and suspected to be 

the etiologic agent in four (Minnesota, 

April 2005; Illinois, June 2006; 

Nebraska, December 2006; and New 

York, March 2006) pool-associated outbreaks. Chemicals are added to pool 

water to protect against microbial and 

algal growth, improve the water quality, maximize the efficacy of the disinfection process (e.g., pH control), and 

prevent corrosion and scaling of equipment. However, these same chemicals 

can become sources of illness or injury 

FIGURE 9 . Recreational water-associated outbreaks of gastroenteritis, by type of 

exposure and etiologic agent— United States, 1997–2006

if they are not properly handled or if water quality and ventilation are poor. In an ARI outbreak in Ohio, a pool 

recirculation pump shut down for unknown reasons, but the 

chemical feed pump continued to feed hypochlorous acid and 

muriatic (hydrochloric) acid into the recirculation system, 

resulting in the release of chlorine gas into the pool that was 

still in use by swimmers when the recirculation pump was 

restarted. Nineteen persons became ill, of whom four of them 

were hospitalized. A dermatitis outbreak (Illinois) was suspected to have resulted from water chemistry deficiencies (pH 

<7 and chlorine level at 0 ppm) that occurred when the automatic chemical-feeding system malfunctioned. These outbreaks underscore the need for engineering controls (e.g., an 

electrical interlock system that shuts down the chemical feed 

pump when the recirculation pump shuts down), regular systems checks, and preventive maintenance of equipment. 

Three additional outbreaks of acute respiratory symptoms 

or eye irritation were suspected to have resulted from an accumulation of chloramines in the water and air of indoor pools. 

Chloramines are disinfection by-products that result from 

chlorine oxidation of nitrogenous compounds (e.g., perspiration, saliva, urine, and body oils) commonly shed into pools 

by swimmers (20). Chloramines are produced in the water 

and volatilize into the surrounding air. In indoor pool settings, chloramines can accumulate in the enclosed space if 

ventilation is inadequate (21). The resulting high levels of 

* These include outbreaks of Salmonella, Campylobacter, Plesiomonas, and mixed pathogens. 

Type of exposure (n = 167) Etiologic agent (n = 167) 

Untreated 

water 

37.7% 

Norovirus 12.0% 

Treated water 

62.3% 

Unidentified 

15.0% 

Etiologic agent: untreated water (n = 63) Etiologic agent: treated water (n = 104) 

Other* 4.2% 

Giardia spp. 3.6% 

Shigella spp. 9.0% 

Escherichia coli 

9.0% 

Cryptosporidium spp. 

47.3% 

E. coli 

19.0% 

Unidentified 

25.4% 

Norovirus 20.6% 

Shigella spp. 

12.7% 

Cryptosporidium spp. 

12.7% 

Giardia spp. 4.8% 

Other* 

4.8% 

Cryptosporidium spp. 

68.3% Unidentified % 

spp. 2. % 

8.7 

E. coli 

Other* 3.8% 

9 

2.9% 

spp. 6.7% 

Norovirus 6.7% 

Giardia 

Shigella 

chloramines can cause ocular, respiratory tract, and mucous 

membrane irritation (20); these high levels in indoor pool 

settings are also potentially linked to asthma (37). The investigation of the Nebraska outbreak, which resulted in one young 

swimmer being admitted to a pediatric intensive-care unit for 

severe chemical epiglottitis and laryngotrach-eobronchitis, 

revealed inadequate facility maintenance that resulted in prolonged deterioration of the water chemistry (e.g., 0.8 ppm free 

chlorine, 4.2 ppm combined chlorine, and a pH = 3.95) (38). 

The shortage of laboratories that perform analyses for airborne chloramines and the variability in indoor air quality 

from day-to-day impedes investigators’ ability to respond to 

reports of ocular and respiratory distress related to indoor pools 

or to obtain rapid and quantitative air measurements at 

implicated pools. Water-testing data useful for evaluating an 

indoor air-quality problem include the pH level and total (i.e., 

free plus combined chlorine) and free chlorine concentrations, 

which can be used to calculate the level of combined chlorine 

in the water. Levels that exceed test kit capacity should be 

re-measured by making dilutions using distilled water. These 

outbreaks underscore the need to train pool operators and 

aquatic staff so that they routinely monitor and maintain water 

chemistry to protect the health of patrons and staff. 

Air-quality improvements in indoor pools will require technological improvements in water chemistry and treatment and 

air circulation and ventilation. New studies suggest that 
20 MMWR September 12, 2008 

installation of ultraviolet treatment devices in pool water 

recirculation systems can reduce pool chloramine levels (39) 

and also can effectively inactivate pathogens (including 

chlorine-resistant Cryptosporidium) (39,40). Plans to improve 

air quality also can be aided by working with the public to 

improve swimmer hygiene. The resulting reduction in urine 

and other nitrogenous waste (e.g., decreased public urination 

in pools and increased showering before entering pools) should 

lead to reductions in chloramine levels in both water and air. 

Such an effort should raise public awareness about the role of 

urine and sweat in creating the irritants associated with 

indoor pool swimming. Operators should encourage showering before entering any pool or spa and facilitate frequent 

bathroom breaks for swimmers, particularly for young children (e.g., instituting adult-only swim times and short 

closures for water-quality testing). 

Multiple challenges are associated with understanding the 

numbers of water-related, chemical illnesses at aquatic venues. Lack of rapid testing and routine testing for chloramines 

suggests that surveillance for recreational water-associated 

outbreaks of acute chemical poisoning is likely to have multiple barriers, resulting in underestimation of the true magnitude of the problem. Acute chemical-related WBDOs might 

be more likely to involve first responders than the traditional 

epidemiologic or environmental health staff investigating other 

WBDOs and reporting to WBDOSS. As a result, more efficient reporting will require building strong and effective intraand interagency communication networks within health 

departments and with other groups (e.g., first responders and 

pool operators) to improve the reporting of WBDOs associated with recreational water. 

Spas 

Spas are susceptible to human contamination by the same 

pathogens that contaminate swimming and wading pools, but 

outbreaks of gastrointestinal illness from spas might be limited because spa usage does not involve as much full body 

(e.g., head-to-toe submersion) activities as pools, resulting in 

less water ingestion. However, spa operation is challenging 

because of difficulty with maintaining disinfectant levels at 

higher water temperatures or with aeration and the relatively 

high bather load to water volume typical of spas. As a result, 

these venues are ideal for amplification of naturally occurring 

environmental contaminants (e.g., thermophilic pathogens, 

P. aeruginosa, and Legionella). 

Skin Infections 

Spa-associated outbreaks are commonly associated with 

dermatitis and folliculitis; P. aeruginosa is the most commonly 

reported agent implicated in these settings (41). During 2005– 

2006, four WBDOs caused by Pseudomonas (Connecticut, 

April 2005; New Mexico, April 2005; Wisconsin, July 2005; 

and Kansas, December 2006), and five WBDOs suspected to 

have been caused by Pseudomonas (Minnesota, March 2005; 

Vermont, February 2005; Georgia, February 2006; Tennessee, March 2006; and Wisconsin, February 2006) were 

reported; four of these outbreaks involved spas, and five 

involved both spas and pools. The frequent co-location and use 

of both spas and pools by patrons means that it can be epidemiologically difficult to implicate a particular pool or spa at a 

single venue. However, amplification of Pseudomonas is most 

likely to occur at the higher temperatures in spas (42). 

Nearly all of the Pseudomonas-associated outbreaks occurred 

as a result of spa use at a hotel, motel, or rented cabin, underscoring the need for improved recreational water quality in 

these transient visitation, travel-associated settings. Multiple 

outbreaks included large gatherings (e.g., birthday pool party 

[Connecticut] and sports tournament [Minnesota]), which 

can rapidly overwhelm the disinfection capacity of spas and 

lead to bacterial amplification. In addition, these gatherings 

often occurred on weekends (Wisconsin), when hotel staff 

trained in spa maintenance are likely to be off duty. Hotels 

and motels should consider having only trained employees 

operate and maintain pools and spas, particularly on weekends when usage is typically highest. Enhanced water-quality 

monitoring and maintenance should be considered when a 

large group or event at a hotel is scheduled. Users should be 

educated about not adding contaminants that might disrupt 

the spa’s water chemistry (e.g., shampoo [Minnesota] and wine 

[Georgia]). 

To prevent spa-associated outbreaks, operators must understand the risk factors and steps that can be taken to limit transmission of pathogens, particularly thermophiles. Proper 

chlorination or bromination effectively kills Pseudomonas and 

other skin-infecting bacteria. A review of 18 Pseudomonas 

outbreaks demonstrated that inadequate disinfection was 

associated with all outbreaks linked to spas (43). Bacterial 

amplification and biofilm build-up can be prevented by properly maintaining spas, ensuring that chlorine or bromine levels consistently remain >2 ppm, and that pH levels remain in 

a range of 7.2–7.8. Poor maintenance of spas has been welldocumented (44), and studies have demonstrated that 

Pseudomonas and other bacteria can remain protected in spa 

biofilms, even in the presence of adequate disinfectant, then 

rapidly proliferate if the disinfectant level drops (42). 

Legionellosis 

Legionellae, which cause both LD and PF, are ubiquitous in 

freshwater environments (45). Environmental conditions in 
Vol. 57 / SS-9 Surveillance Summaries 21 

whirlpool spas (e.g., warm temperatures and water aerosolization) promote the amplification and transmission of the bacteria when combined with low or erratic disinfectant levels. 

Exposure to Legionella is more likely to occur in the absence 

of adequate levels of disinfectant, underscoring the importance of maintaining adequate disinfectant levels and pH control. When lapses in preventive measures result in a legionellosis 

outbreak, morbidity can be reduced by rapid recognition of 

the outbreak, identification of its source, and immediate implementation of remediation. Remediation methods include 

cleaning and disinfecting the spa to eliminate Legionella colonization and performing follow-up cultures for Legionella to 

ensure that re-colonization does not occur (46). 

All eight legionellosis WBDOs associated with recreational 

water during 2005–2006 were associated with spas. Five of 

these outbreaks occurred at hotels which highlights the role 

of travel in Legionella transmission and illustrates the potential difficulty of detecting travel-associated illnesses when travelers disperse to their resident state or country. CDC’s 

supplementary reporting system for legionellosis collects 

exposure and travel information. In a 2005 CSTE position 

statement (http://www.cste.org/PS/2005pdf/final2005/05­

ID-01final.pdf), surveillance and active follow up of potential travel-associated case reports was recommended position 

statement to improve detection of travel-associated clusters of 

illness and to increase opportunities for disease prevention. 

During 2005–2006, a total of 10 clusters were identified (47) 

although not all met WBDO definition. After CSTE’s recommendations in 2005, CDC 1) improved communication 

with international, state, and local public health partners concerning travel-associated LD cases; 2) developed a standardized notification and tracking system; and 3) created a dedicated 

e-mail address for case reporting (travellegionella@cdc.gov). In 

addition, CDC’s legionellosis website (http://www.cdc.gov/ 

legionella) has been updated to provide useful tools for investigating legionellosis outbreaks (including sample questionnaires), 

sample letters for hotel management, and protocols for environmental assessments of water systems. 

Interactive Fountains/Wet Decks 

and Fill-and-Drain Pools 

Infectious Gastroenteritis 

Certain treated water venues (e.g., interactive fountains, 

which also are called wet decks or spray parks) might be overlooked as potential sites for transmission of infection or pool 

regulation because they do not have standing water as traditionally found in swimming pools. These venues are particularly prone to contamination by fecal material, vomit, and 

dirt because of the young users of the small volume of recirculating water. These contaminants can potentially drain into 

the water reservoir and be sprayed back on users, increasing 

the likelihood of contaminated water ingestion. The use of 

interactive fountains has previously been associated with outbreaks of gastroenteritis (48), and outbreaks reported here 

(Louisiana, August 2005; New York, June 2005; California, 

July, 2006; and Florida, May 2006) demonstrate that transmission continues to occur in these settings. Not all states 

regulate interactive fountains which might increase chance of 

improper design, maintenance, or operation in these venues. 

In one of the largest outbreaks reported to the WBDOSS, 

approximately 2,300 persons developed cryptosporidiosis following exposure to a New York spray park. The environmental 

investigation revealed that recycled water was not adequately 

filtered and disinfected. In response, New York passed emergency legislation requiring that supplementary disinfection (e.g., 

ultraviolet radiation or ozonation) be installed on water returning through the sprayers. Designs that improve water treatment 

for these interactive fountains are needed to reduce the risk for 

RWIs. Reports of investigations from three additional 

cryptosporidiosis outbreaks (California, 2006; Florida, 2006; 

and New York 2005) indicated inadequate disinfection levels 

(<1.0 ppm chlorine) and the use of sand or cartridge filters, 

both of which might not be adequate for Cryptosporidium 

oocyst removal. Filters with diatomaceous earth might be more 

effective at removing oocysts than sand or cartridge filters. 

The use of tap water to fill or operate temporary aquatic 

venues (e.g., fill-and-drain pools) used by young children continues to be a public health challenge (California, July 2006; 

and Wyoming, July 2005). Lack of disinfection and the traditional use by toddlers and diaper-aged children have resulted 

in multiple outbreaks being associated with use in both residential and institutional settings (12,49,50). In the California outbreak, nine persons became ill with AGI after attending 

a pool party where guests swam in a plastic pool filled with 

untreated tap water. Three children were hospitalized; S. sonnei 

was confirmed in stool samples from six ill persons. In Wyoming, an outbreak of campylobacteriosis occurred after two 

families filled a pool with untreated water from a shallow well. 

In addition, a dog known to roll around in cow feces entered 

the pool. The potential risk for infection associated with 

using temporary pools filled with tap water without 

additional disinfection and filtration should be considered 

before they are used in residential settings. To reduce the risk 

for pathogen transmission, persons with gastroenteritis should 

be excluded, and the pool should be drained and cleaned daily. 

On the basis of documented outbreaks, fill-and-drain pools 

should be eliminated from institutional settings or large group 

events (50). 
22 MMWR September 12, 2008 

Lakes and Rivers 

Infectious Gastroenteritis 

Although the proportion of AGI outbreaks associated with 

untreated venues (e.g., lakes and rivers) relative to treated venues decreased over the previous decade, the number of outbreaks associated with untreated venues has remained relatively 

constant (Figure 10). During 2005–2006, a total of 13 outbreaks of gastroenteritis associated with untreated freshwater 

venues were reported; all of these were linked to swimming in 

lakes or ponds. Freshwater venues have a higher proportion 

of outbreaks caused by bacterial and viral etiologic agents compared with treated water venues (Figure 5). 

Multiple studies have determined the utility of water-quality 

monitoring (16) for assessing the associated risk for swimmer 

illness (18) in large bodies of water (e.g., Great Lakes and the 

ocean). However, the small inland water bodies associated with 

the outbreaks in this report do not have consistent external 

sources of contamination (e.g., sewer overflow), suggesting 

that swimmers might be an important source of water contamination and infection transmission. As with treated venues, human behavior plays a key role in the spread of pathogens 

in untreated bodies of water. Modification of swimmer 

behavior might be a more critical factor in natural water venues that lack the benefit of disinfection and filtration barriers 

to transmission. Recommendations for swimmer hygiene in 

natural waters are the same as those previously discussed for 

treated pools. In addition, beach managers and swimmers 

should be aware that shallow, poorly circulated swimming 

areas, although desirable to many swimmers, might pose a 

higher risk of exposure to certain pathogens compared to 

deeper, well circulated swimming areas. Potential methods to 

improve circulation of water through beach areas should be 

explored to reduce the longevity of focal, swimmer-derived 

contamination and waterborne-disease transmission. Reducing exposure to high fecal indicator bacterial levels at sites 

affected by runoff can be achieved by avoiding swimming 

immediately after heavy rainfall (reducing exposure to any 

increase in contaminated runoff) and by not swimming near 

storm drains or pipes that might release contamination into 

water bodies (24). 

Primary Amebic Meningoencephalitis 

During 2005–2006, five fatal cases of PAM caused by 

N. fowleri were reported; for two of these cases, there was possibly a common exposure to either a creek or a small spray 

park. For the remaining three cases, no common exposure 

was identified (Tables 4, 10). This rare disease is of public 

health importance because of the high fatality rate associated 

with infection (>99%) (51) and the public alarm it raises for 

FIGURE 10. Number of recreational water-associated outbreaks 

of gastroenteritis (n = 259), by water type and year — United 

States, 1978–2006 

5

10

15

20

25

Treated

Untreated

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006

0

Year

use of natural waters in the southern tier states in the United 

States. N. fowleri is a free-living ameba that proliferates in 

warm freshwater and hot springs. Disease occurs when the 

ameba coincidentally enters the nasal passages, travels to the 

olfactory lobe of the brain, and infects brain tissue. The five 

cases all occurred in southern tier states (Arizona, Georgia, 

Oklahoma, and Texas) during warm weather months 

(Tables 4, 10). Three of the five children who died of PAM 

during 2005–2006 had participated in activities in warm 

water before onset of symptoms, similar to other known cases 

of PAM. The source of exposure for the two Oklahoma cases 

could not be determined despite a public health investigation. 

The low number of Naegleria infections makes it difficult 

to determine why certain persons become infected compared 

with the millions of others with the same or similar exposures 

to waters across the United States. As a result, the efficacy of 

existing risk-reduction strategies are uncertain. The finding 

of Naegleria in the majority of lake water surveys conducted 

in southern tier states suggests that this minimal likelihood of 

Naegleria infection always will be associated with swimming 

in warm, freshwater lakes, rivers, and hot springs. While the 

most certain way to prevent infections is to refrain from swimming in these freshwater bodies, swimmers might reduce their 

risk for PAM by not swimming or jumping into bodies of 

warm freshwater, hot springs, and thermally polluted water 

(e.g., water around power plants); not swimming or jumping 

into freshwater during periods of high water temperature and 

low water volume; holding the nose shut or using nose clips 

when jumping or diving into bodies of warm freshwater; and 

refraining from digging in or stirring up sediment while swimming in shallow, warm, freshwater areas. CDC is collaborating with CSTE to more effectively describe the scope of 

Naegleria infections in the United States, improve surveillance, 

and analyze available exposure and environmental occurrence 

data to develop more evidence-based risk-reduction measures 

and messages (52). 
Vol. 57 / SS-9 Surveillance Summaries 23 

Leptospirosis 

Although infections caused by Leptospira are considered to 

be more common in tropical and semitropical areas of the 

world (53), outbreaks reported during 2005–2006 illustrate 

the potential risk for leptospirosis outbreaks associated with 

recreational water contact in the United States. Leptospira can 

be found in the urine of infected wild and domesticated animals, so contamination of natural waters can occur where 

infected animals live. The route of transmission in humans 

usually is through contaminated water contact with broken 

or abraded skin or through contact with the mucosal surfaces 

of the eye, mouth, nasopharynx, or esophagus. Exposure might 

also occur through inhalation, ingestion, or prolonged 

immersion in water, resulting in increased permeability of the 

skin. Increased skin permeability might play a role in infections resulting from contact with contaminated surface water 

after flooding (54) or with prolonged use of contaminated 

surface waters as part of sports or other events (e.g., triathlons) 

(55,56). Two outbreaks of leptospirosis involving 46 persons 

were reported for 2005–2006 as well as a previously unreported outbreak in Hawaii in 2004 (57). One outbreak in 

California (July 2005) was associated with persons working 

in a drought-affected stream. The second larger outbreak 

occurred in Florida (November 2005) and was associated with 

participation in an adventure race. This is consistent with previous outbreaks in other similar competitive venues (55,56). 

To reduce risk for infection, persons should wear protective 

clothing, avoid swimming when they have open wounds or 

abrasions and avoid water contaminated by animal urine. 

Cercarial Dermatitis 

During the 2005–2006 surveillance period, two WBDOs 

of suspected cercarial dermatitis caused by avian schistosomes 

were reported (California, July 2005 Ohio August 2006). 

Although the diagnosis was not confirmed, this self-limited 

disease is known to occur among persons exposed to lakes 

across the United States where infected birds contaminate water 

supporting the intermediate host snail (58). The risk for 

acquiring cercarial dermatitis might be reduced by warning 

swimmers of potentially contaminated lakes, avoiding 

shallow swimming areas where infected snails reside, instituting a snail control program, and by not attracting birds to 

swimming areas (e.g., by not feeding them). 

Marine Water 

No waterborne disease outbreaks associated with marine 

waters were reported to WBDOSS before 2005–2006; however, evidence from multiple sources demonstrates that contamination of marine waters is common and that swimmers 

in marine waters are at increased risk for acquiring AGI 

(23,59). States and territories report water-quality testing 

results and notification data for their coastal and Great Lakes 

recreational water to EPA. In 2006, 32% of monitored beaches 

were affected at least once by either an advisory or closing as a 

result of the EPA microbial fecal indicator limits being 

exceeded or water-quality standards not being met (17). Multiple studies have linked these water-quality indicators with 

increased risk for RWIs (23,59,60), although RWIs also can 

occur when water-quality indicators are within established limits (24). The reasons for a lack of reported marine-associated 

outbreaks might include the wide geographic spread of 

beachgoers, the fact that some of the marine-associated illnesses are not enteric illnesses typically linked to waterborne 

causes, and a lack of illness attribution to marine waters. 

Vibrio Illness 

Although WBDOs associated with marine waters might be 

difficult to detect, single cases of Vibrio infections from 

marine water exposure might be more likely to be reported 

because of the severity of the illness associated with infection. 

The number of Vibrio infections associated with water exposures during 2005–2006 (n = 189) was higher than the number reported in 2003–2004 (n = 142), although recreational 

water exposure constitutes only a small fraction (14.7%) of 

the 1,287 vibriosis cases from all exposures reported in 2005– 

2006 (61). Some of the increase in reported cases for 2005 

might be attributable to flood water exposure in the Gulf Coast 

immediately following Hurricane Katrina (62) when active 

case-finding facilitated identification of Vibrio infections. 

Reported hurricane-related infections were primarily among 

persons with wounds who waded through flood waters. The 

majority of hurricane-related Vibrio infections were caused by 

V. vulnificus, which predominately occurs in the Gulf Coast. 

Wound infections from V. vulnificus can cause severe illness 

and sequelae, including septicemia and the need for amputation. For nonfoodborne cases of V. vulnificus infection, the 

hospitalization rate is approximately 90% and the case fatality rate is 17%–24% (63,64), similar to the 22.3% case fatality rate among cases reported during 2005–2006 (Table 8). 

Disease is more common and severe among persons with preexisting wounds and other medical conditions (e.g., diabetes, 

heart disease, or liver disease) (64,65). V. parahaemolyticus and 

nontoxigenic V. cholerae infections were also reported among 

persons with hurricane-related Vibrio infections. The burden 

of wound-related vibriosis is unknown, although an estimated 

8,000 Vibrio infections occur annually, including an estimated 

2,800 annual cases not associated with food exposure (64). 

CSTE added vibriosis to the list of nationally notifiable diseases in January 2007. Vibriosis is reportable in 35 states, 
24 MMWR September 12, 2008 

although all other states and territories can report vibriosis 

cases to CDC. Cases are reported to CDC by using the Cholera and Other Vibrio Illness Surveillance report form, which 

is available at http://www.cdc.gov/nationalsurveillance/PDFs/ 

CDC5279_COVISvibriosis.pdf. Annual summaries of 

national data on vibriosis are available at http://www.cdc.gov/ 

nationalsurveillance/cholera_vibrio_surveillance.html. 

Improved surveillance and reporting are designed to increase 

understanding of the magnitude and distribution of Vibrio 

illness related to marine water, to better characterize the risk 

and contributing environmental factors, and to guide the 

development of appropriate prevention messages (e.g., persons with wound or certain preexisting conditions not swim 

in warm marine water). 

Seabather’s Eruption 

One outbreak was reported for 2005–2006 in which swimmers were exposed to marine water. Certain ill persons had 

symptoms consistent with Seabather’s Eruption, a skin condition caused by contact with toxins from stinging jellyfish 

larvae. However, the majority of persons also exhibited an 

influenza-like illness which, although previously associated 

with Seabather’s Eruption (66), could also indicate another 

water-associated etiology. Seabather’s Eruption occurs primarily in the marine waters off Florida, the Gulf of Mexico, and 

the Caribbean Sea particularly during spring and summer 

months. Whereas risk factors associated with developing 

Seabather’s Eruption are not fully understood, swimmers might 

be able to reduce their risk by removing bathing suits and 

thoroughly showering to remove jellyfish larvae after marine 

water exposure (67). Ongoing research is needed to understand the water conditions that lead to increased risk for illness among swimmers so that appropriate risk-reduction 

messages can be given to ocean beach visitors. 

Previously Unreported Outbreaks 

The retrospective review of waterborne-disease outbreaks 

in Minnesota, New York, and Tennessee by EHS-Net Water 

staff resulted in the reporting of 30 previously unreported recreational water–associated outbreaks and case reports 

(Table 11). The addition of previously unreported outbreaks 

increases understanding about the epidemiology of waterborne 

disease in these jurisdictions. The success of the EHS-Net 

Water surveillance improvement effort underscores the utility 

of acquiring personnel who can focus on waterborne disease 

detection, investigation, and reporting (13). An additional 

outbreak from 2004 was reported by Hawaii (57). 

Aquatic Facility-Related Health Events 

not Associated with Recreational Water 

Use 

All 32 aquatic facility–related health events not associated 

with recreational water use (Table 12) were reported by New 

York, which had captured these events through a system, which 

mandates reporting of chemical injuries. Three events, all of 

which involved mixing of incompatible pool chemicals that 

resulted in the release of chlorine gas, were reported during 

2005–2006. The first outbreak of ARI resulted from a spill of 

50–75 gallons of hypochlorous acid (i.e., bleach), which might 

have interacted with other chemicals in the spill area. The second event resulted from using a container that was previously 

used for hypochlorous acid as a container for the acid used to 

adjust pool pH. Subsequent contact of the pool acid with the 

hypochlorous acid residue released a chlorine gas plume. The 

third event involved adding both calcium hypochlorite (chlorine) and trichloro-s-triazinetrione (a chlorinated isocyanurate 

commonly called trichlor) to the pool chlorinator system, which 

resulted in a release of chlorine gas. The material safety data 

sheet for trichloro-s-triazinetrione states that it is not to be 

mixed with other chemicals, especially calcium hypochlorite; 

alkalis; and other swimming pool/spa chemicals in their concentrated forms. These events and others (Table 12) highlight 

the need for new or improved 1) pump room and chemical 

storage area design and construction (e.g., improved ventilation, and chemical containment and separation), 2) chemical 

packaging (e.g., to easily differentiate between key pool chemicals), 3) chemical storage (e.g., to prevent mixing accidents), 

4) staff training on how to safely store and handle chemicals 

and maintain and repair chemical-using pool systems, and 5) 

emergency response protocols. 

Prevention 

Prevention of RWIs is likely to be accomplished only through 

a concerted team effort by public health professionals, swimming venue operators, and the general public. Operators at 

treated water venues are equipped with various methods that 

should be employed to prevent outbreaks. The traditional 

reliance on two water-treatment barriers at treated water venues, 

chlorination and filtration, likely needs to be expanded to 

include in-line (i.e., usually installed after filtration and before 

chlorination) supplemental disinfection (e.g., ultraviolet treatment and ozonation) to increase the level of protection against 

pathogens, particularly chlorine-resistant Cryptosporidium. Such 

supplemental disinfection systems will not eliminate waterbornedisease transmission (because these systems are circulationtime dependent), so improved monitoring of water-quality and 
Vol. 57 / SS-9 Surveillance Summaries 25 

facility-maintenance programs and improved policies to educate the public and decrease contamination of aquatic facilities with bodily waste also are critical. In response to the lack 

of protective barriers at untreated swimming venues (e.g., lakes 

and oceans), beach managers and public health officials should 

implement water-quality testing programs and educate swimmers concerning appropriate prevention measures (e.g., not 

swimming after heavy rainfall). Specific efforts should 

address environmental pathogens unlikely to be prevented by 

current water-quality guidelines (e.g., illnesses caused by Vibrio 

and otitis media infections). 

Public health professionals should 1) improve training for 

pool inspectors, 2) update and improve pool codes to stay 

current with changing designs and needs demonstrated by 

outbreaks summarized in this report, 3) lead and collaborate 

with aquatic staff to educate the general public, and 4) 

develop expertise in detecting and investigating recreational 

water-associated outbreaks, particularly those associated with 

chemicals. Safe handling and use of chemicals at aquatic 

facilities needs to be a standard training element that is regularly reinforced. In addition, to improve overall indoor air 

quality, public health professionals and pool managers need 

to understand the importance of implementing improvements 

in pool water quality, swimmer hygiene, air-turnover rates, 

and ventilation. 

Educating swimmers can play a vital role in reducing RWIs 

by encouraging them to follow basic guidelines for healthy 

swimming. Fecal shedding of pathogens is common (36), so 

reducing the risk for water-related infection is best achieved 

by implementing diarrhea-exclusion policies, using appropriate hygiene measures, and advising the public to avoid swallowing recreational water. In addition, the public can 

inform themselves about RWI prevention. They can 

become activist swimmers (e.g., checking chlorine and pH levels themselves) and advocate for healthy swimming venues. 

Conclusion 

Data collected by WBDOSS are used to characterize the 

epidemiology of waterborne disease and outbreaks associated 

with both recreational and drinking water. Swimming is a 

common activity in the United States (68). Certain diseasecausing agents are transmitted through shared bodies of water, 

and new waterborne pathogens that infect humans (e.g., 

Cryptosporidium and toxigenic E. coli) have emerged in the 

previous 3 decades. RWIs and outbreaks are associated with 

both treated and untreated water and with every type of aquatic 

venue. Common themes derived from the outbreaks in this 

report include 1) low disinfectant levels or poor filtration; 2) 

inadequate water-quality monitoring; 3) high bather loads 

during large events; 4) breakdowns of equipment and delayed 

detection or repair times; 5) not using ultraviolet radiation or 

ozonation to treat for Cryptosporidium in pools and interactive fountains; 6) accumulation of combined chlorines in pools 

accompanied by inadequate indoor air ventilation; 7) inadequately trained aquatic staff, particularly on safe chemical 

handling practices, 8) lack of communication within and 

between public health agencies; 9) outbreaks occurring on 

weekends when trained staff might be off duty; 10) lack of 

awareness by the general public of appropriate healthy swimming behaviors; and 11) lack of health department familiarity with chemical-associated RWIs. 

Although no easy solution exists for reducing WBDOs 

associated with recreational water, a sustained effort by the 

swimming public, the aquatic management sector, and public health agencies can reduce the associated risk. The millions of persons in the United States who use recreational water 

every year can best reduce their risk by staying informed 

regarding the health and safety concerns associated with swimming. Public health officials should lead this educational 

effort to promote healthy swimming behaviors. Prevention 

methods discussed in this report should help make swimming 

experiences healthier, safer and more enjoyable. The aquatic 

sector also can benefit from the recommendations, which 

address changes that are needed in operation, maintenance, 

and chemical handling procedures. Large numbers of violations of state and local pool codes occur each year (15,44), 

indicating that improved pool operation, disinfection policies, and enforcement are needed to prevent RWIs (33). In 

addition, improvements in indoor air quality monitoring and 

widespread dissemination of validated testing protocols are 

needed to support improved air quality in indoor swimming 

pool settings. As a result of recommendations from a 2005 

national workshop on how to prevent RWIs, CDC is sponsoring development of a national model aquatic health code 

(MAHC), which involves public health and aquatics sector 

personnel from across the country and is designed to transform the typical health department program into a data-driven, 

knowledge-based, risk-reduction effort to prevent disease and 

injuries and promote healthy recreational water experiences. 

MAHC will provide uniform guidelines for the design, construction, operation, and maintenance of swimming pools and 

other disinfected swimming venues. Although nonregulatory 

in nature, the MAHC should ensure that the best available 

standards and practices for protecting public health are available for adoption by state and local agencies. Further information is available at http://www.cdc.gov/healthyswimming/ 

model_code.htm. 
26 MMWR September 12, 2008 

Public health professionals at all levels of government should 

lead a multidisciplinary approach to prevent RWI that 

includes surveillance, health education, epidemiologic studies, laboratory support, and environmental health research. 

Educational resources and campaigns are needed for swimmers, parents, aquatic venue operators, and public health staff. 

Improved communications, particularly during outbreak 

investigations, between all areas of the public health system 

(e.g., infectious disease, environmental health, and surveillance staff) and between agencies in neighboring jurisdictions 

can 1) enhance awareness concerning ongoing occurrences of 

RWIs, 2) facilitate reporting to WBDOSS in a timelier manner, and 3) strengthen WBDO investigations and responses 

to protect the public. The timely collection of clinical specimens and water samples for testing during a WBDO investigation and prompt initiation of an environmental investigation 

will result in more rapid identification of the etiologic agent 

and determination of the conditions leading to the outbreak. 

However, the capacity of public health departments and laboratories to detect and investigate potential WBDOs varies and 

needs to be strengthened to meet these challenges. WBDO 

investigations typically require input from various disciplines, 

including infectious disease epidemiology, environmental 

health, clinical medicine, water and sanitation engineering, 

chemists/toxicologists, and microbiology. Additional crosstraining of existing personnel in these areas or additional staffing and resources are needed to improve WBDO detection, 

investigation, and reporting. Other methods of improving 

surveillance at the local, state, and federal levels include additional review and follow-up of information gathered through 

other mechanisms (e.g., media reports or emergency responder 

reports of illness associated with recreational water venues). 

CSTE passed a 2006 position statement making waterbornedisease outbreaks, as a unit of reporting, nationally notifiable 

and reportable to CDC starting in 2007. Adoption of this 

CSTE recommendation at the state level through statespecific legislative action might improve reporting of waterborne outbreaks. In addition, to improve timeliness and 

completeness of reporting, CDC and EPA are collaborating 

with public health jurisdictions to implement electronic 

reporting of WBDOs through the National Outbreak Reporting System (NORS). NORS will be a more systematic data 

collection tool that will provide public health agencies and 

waterborne-disease researchers with the evidence base they need 

to identify the causes of WBDOs and understand the interrelated factors contributing to these outbreaks. 

EHS-Net Water, a collaborative project between EPA, CDC, 

and five state health departments, is an effort to improve 

WBDO identification, investigation, response, and reporting. 

Environmental health specialists initially focused on understanding their state-specific surveillance systems, leading to 

the reporting of numerous historical outbreaks to WBDOSS. 

Although this project has focused primarily on improving 

drinking water-associated disease outbreak surveillance, it also 

has markedly improved our understanding of recreational 

water-associated outbreaks in EHS-Net Water states, which 

demonstrates the value of investing water-specific resources 

in certain jurisdictions. 

Focusing on improving awareness, training, resources, and 

communication will improve the quality of the data in 

WBDOSS. These efforts should make public health activities 

related to waterborne disease more efficient and, in turn, 

reduce the burden of recreational water-associated disease and 

injury (Box). 

Acknowledgments 

The authors thank the following persons for their contributions 

to this report: state, local, and territorial waterborne-disease 

surveillance coordinators; state, local, and territorial epidemiologists 

and environmental health personnel; Mark Eberhard, PhD, Monica 

Parise, MD, Bonnie Mull, MPH, Division of Parasitic Diseases, 

National Center for Zoonotic, Vector-Borne, and Enteric Diseases, 

CDC; Lorraine Backer, PhD, Division of Environmental Hazards 

and Health Effects, National Center for Environmental Health, 

CDC; Charles Otto, Vince Radke, MPH, Division of Emergency 

and Environmental Health Services, National Center for 

Environmental Health, CDC; Sean Shadomy, DVM, MPH, 

Division of Foodborne, Bacterial and Mycotic Diseases, National 

Center for Zoonotic, Vector-Borne, and Enteric Diseases, CDC. 

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Vol. 57 / SS-9	 Surveillance Summaries 27 

BOX. Organizations that provide assistance in investigations of waterborne diseases and outbreaks (WBDOs) associated with 

recreational water exposure 

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— Pool and spa operation guidelines, including •	 Requests for Testing for Bacterial Enteric 

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• Information Regarding Beaches Enteric Diseases 

Coordinating Center for Infectious Diseases, CDC
 EPA Internet: http://www.epa.gov/OST/beaches 

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30 MMWR September 12, 2008 

Appendix A
 

Glossary of Definitions
 

aquatic facility-related health Chemical injury cases and outbreaks (e.g., mixing of pool chemicals that release toxic gas) 

events not associated with at aquatic facilities in which exposure to water was not the cause of illness. Although these 

recreational water events are not classified or analyzed as waterborne-disease outbreaks, they highlight 

important public health and safety concerns related to the design, operation, and maintenance of recreational water venues. 

backwash Flow of water through filter element(s) or media in a reverse direction to dislodge accumulated dirt, debris, and/or filter aid, and remove them from the filter tank. 

backwash cycle Time required to thoroughly backwash the filter system. 

bather load The number of bathers using a swimming pool or spa at any one time. The maximum 

bather load is usually determined by a state or local pool code, based on surface area and 

depth of the pool or spa. 

biofilm Microbial cells that adhere to a surface through a matrix of primarily polysaccharide materials in which they are encapsulated. These can grow on piping and surfaces of aquatic 

venues and can be notoriously difficult to remove. They offer protection to microbes from 

disinfectants (e.g., chlorine) in the water. 

cercarial dermatitis Dermatitis caused by contact with or direct invasion through the skin or a break in the 

skin by the cercariae (larval stage) of certain species of schistosomes, a type of parasite, for 

which the normal hosts are birds and nonhuman mammals. Dermatitis is an allergic 

response to contact with cercariae and does not lead to parasitic infestation in humans and 

produces no long-term disease. 

class Waterborne disease and outbreaks are classified according to the strength of the epidemiologic and laboratory data implicating recreational water as the source of the disease or 

outbreak (see Table 1). 

chloramines A group of disinfection by-products or weak disinfectants formed when free chlorine 

combines with nitrogen-containing compounds in the water (e.g., urine or perspiration). 

Tri- and di-chloramine can cause eye, skin, lung, and throat irritation and can accumulate 

in the water and air surrounding treated recreational water venues. In drinking water treatment, monochloramine is used for disinfection to reduce formation of disinfection 

by-products created when using chlorine as a disinfectant (see combined chlorine level). 

coliforms All aerobic and facultative anaerobic, gram-negative, nonspore-forming, rod-shaped 

bacteria that ferment lactose with gas formation within 48 hours at 95oF (35oC). 

combined chlorine level See chloramines. Chlorine that has combined with organic compounds in the water and is 

no longer an effective disinfectant for recreational water. This value is derived by subtracting the free chlorine test level from total chlorine test level. The combined chlorine level is 

likely to include combined compounds in addition to chloramines. 

contact time The length of time water (and pathogens) is exposed to a disinfectant, usually measured in 

minutes (e.g., chlorine contact time). 
Vol. 57 / SS-9 Surveillance Summaries 31 

Cryptosporidium The taxonomy of Cryptosporidium has evolved as a result of advancements in molecular 

methodology and genotyping. The former C. parvum now refers to a species that is zoonotic 

and infects ruminants and humans. C. hominis refers to the species of Cryptosporidium that 

infects only humans, primates, and monkeys. Both species were referred to previously as 

C. parvum. 

dermatitis Inflammation of the skin. In this Surveillance Summary, the term dermatitis is used to denote 

a broad category of skin-related symptoms (e.g., folliculitis, cellulitis, burns, or rash). 

disinfection by-products Chemicals formed in water through reactions between organic matter and disinfectants. 

Includes chloramines, also known as combined chlorines. 

etiologic agent The pathogen, chemical, or toxin causing a waterborne disease or outbreak. Infectious 

etiologic agents include bacteria, parasites, and viruses. 

fecal coliforms Coliforms that grow and ferment lactose to produce gas at 112.1oF (44.5oC) within 24 hours. 

fill-and-drain pools Small pools, often constructed of plastic, which might be inflatable, and filled with tap 

water without any ongoing chemical disinfection or filtration. Sometimes called kiddie pools. 

filtration The process of removing suspended particles from water by passing it through one or more 

permeable membranes or media of limited pore diameter (e.g., sand, anthracite, or diatomaceous earth). 

folliculitis Inflammation of hair follicles. Spa-associated folliculitis is usually associated with infection by Pseudomonas aeruginosa. 

free chlorine The chlorine in water not combined with other constituents; therefore, it is able to serve as 

an effective disinfectant (also referred to as free available chlorine or residual chlorine). 

Measuring the free chlorine level is a common water-quality test. 

freshwater (untreated water) Surface water (e.g., water from lakes, rivers, or ponds) that has not been treated in any way 

to enhance its safety for recreational use. 

interactive fountain A fountain or water spray device intended for (or accessible to) recreational use. They 

usually do not have standing water as part of the design. These are sometimes called spray 

pads, splash pads, wet decks, or spray grounds. In contrast, noninteractive (ornamental) 

fountains intended for public display rather than recreational use are often located in front 

of buildings and monuments, and their water is not easily accessible for public use. 

marine water Untreated recreational water at an ocean or estuarine setting. 

microcystin toxin A secondary metabolite of blue-green algae (cyanobacteria) that can have toxic effects on 

humans and animals, potentially causing a wide range of illness or even death when exposure to accumulated toxins in fresh or marine water occurs. 

mixed agent outbreak More than one type of etiologic agent is identified in clinical specimens from affected 

persons, and each etiologic agent is found in >5% of positive clinical specimens (e.g., an 

outbreak with Giardia spp. [parasites] and Salmonella spp. [bacteria], with each agent 

identified in >5% of stool specimens). 

oocyst The infectious stage of Cryptosporidium species and certain other coccidian parasites with 

a protective wall that facilitates survival in water and other environments and renders the 

parasite extremely resistant to chlorine. 
32 MMWR September 12, 2008 

predominant illness The type of illness most commonly expressed in a substantial proportion (>50%) of 

patients (e.g., gastroenteritis, dermatitis, and acute respiratory illness). When more than 

one illness type seems to define the character of the waterborne disease and outbreak, they 

are listed together as predominant illnesses. 

recreational water venue A body of water used for the purpose of recreation (e.g., swimming, soaking, or athletics), 

including any structure that encloses this water. It can include lakes and ponds, rivers, 

springs, the ocean, and man-made venues (e.g., swimming pools, spas, and water parks) 

that do not necessarily include standing water (e.g., interactive fountains). 

reservoir, impoundment An artificially maintained lake or other body of water created for the collection and storage 

of water. This body of water might be available for recreational use. 

setting Location where exposure to contaminated water occurred (e.g., swimming beach, water 

park, and hotel). 

spa Any structure, basin, chamber, or tank (located either indoors or outdoors) containing a body 

of water intended to be used for recreational or therapeutic purposes that usually contains a 

waterjet or aeration system. It is operated at high temperatures and is usually not drained, 

cleaned, or refilled after each use. It sometimes is referred to as a hot tub or whirlpool. 

spray park A recreational water venue solely consisting of multiple interactive fountains. 

total chlorine A common water-quality test that measures the chlorine in water that is free for disinfection (free chlorine) plus that combined with other organic materials (combined chlorine). 

The combined chlorine level is derived by subtracting the free chlorine test result from the 

total chlorine test result. 

total coliforms Nonfecal and fecal coliforms that are detected by using a standard test. 

treated water Water that has undergone a disinfection or treatment process (e.g., chlorination and filtration) for the purpose of making it safe for recreation. Typically, this refers to any recreational water in an enclosed, manufactured structure but might include swimming or 

wading pools, fountains, or spas filled with treated tap water (e.g., small wading kiddie 

pool) or untreated water (e.g., mineral spring water) that receives no further treatment. 

turbidity A measurement of suspended particulate matter in water expressed as nephelometric turbidity units (NTU). 

turnover rate The time required to theoretically recirculate the entire volume of water in a swimming 

pool, spa, or hot tub. 

ultraviolet light The segment of the light spectrum between 100-300 nanometers (nm). 

ultraviolet light disinfection unit A device that produces ultraviolet light between 250-280 nm for the purpose of inactivation of microorganisms by UV radiation. 

untreated water Surface water that has not been treated or disinfected in any way (i.e., lakes, rivers, oceans, 

and reservoirs). 

user Any person using a pool, spa, or hot tub and adjoining deck area. 

Vibrio species A genus of comma-shaped, gram-negative Proteobacteria that include various human pathogens. Certain species are found in salty or brackish water and can cause illness by contamination of a wound or epithelial site (e.g., eardrums or sinus cavities). Sequelae can include 

sepsis and death. 
Vol. 57 / SS-9 Surveillance Summaries 33 

waterborne-disease outbreak Water exposure in which two or more persons have been epidemiologically linked to recreational water by location of exposure, time, and illness. 

waterborne disease and outbreak The surveillance system that contains the outbreaks and case reports reported by jurisdictional 

surveillance system (WBDOSS) public health authorities. Inputs into this system are illustrated in Figure 1. 

WBDOSS Surveillance Summary The biennial summaries of waterborne-disease outbreaks and cases associated with recreational water, drinking water and water not intended for drinking are published in the 

MMWR. These publications also discuss waterborne-disease data from other surveillance 

systems (e.g., Vibrio) and disseminate waterborne-disease prevention messages. 

water-quality indicator A microbial, chemical, or physical parameter that indicates the potential risk for infectious 

diseases associated with using the water for drinking, bathing, or recreational purposes. 

The best indicator is one with a density or concentration that correlates best with health 

effects associated with a type of hazard or pollution (e.g., turbidity, coliforms, fecal coliforms, 

Escherichia coli, enterococci, free chlorine level). 
34 MMWR September 12, 2008 

Appendix B 

Descriptions of Selected Waterborne Disease and Outbreaks Associated 

with Recreational Water Use 

State in No. of 

which WBDO cases 

Date occurred Etiologic agent (deaths) Description of WBDO 

Bacteria 

July 2005 Wyoming Campylobacter jejuni 6 Two families celebrated a holiday weekend together at a private 

residence. A small pool was set up for the adults and treated with a 

jug of bleach. A fill-and-drain pool (kiddie pool) was set up for the 

children and filled with untreated well water. A dog known to roll 

around in cow feces might have introduced fecal matter into the 

children’s pool. Five children, ranging from ages 13 months–8 years, 

and one adult developed gastrointestinal illness. Stool specimens from 

two of the children tested positive for Campylobacter. 

July 2005 California Leptospira spp. 3 Three men became ill and were diagnosed with laboratory-confirmed 

leptospirosis after removing brush and picking berries in a stream near 

their homes. The stream was very low and slow-flowing at the time of 

exposure. 

November 2005 Florida Leptospira spp. 43 Racers from approximately 30 U.S. states and two Canadian 

provinces were exposed to surface water from multiple sources, 

including creeks, swamps, and a river during an endurance race. In 

all, 192 (96%) of the racers were interviewed to collect information 

about exposures and signs and symptoms of illness. Mean incubation 

times were similar for suspected cases (12.8 days) and confirmed 

cases (13.5 days). The most common symptoms reported were fever 

(100%), headache (91%), chills (69%), sweats (68%), and muscle/joint 

pain (68%). Swallowing river and swamp water and being submerged 

were significantly associated with developing illness. 

January 2006 Florida Legionella 11 (1) Eleven persons became ill (3 confirmed Legionnaires’ disease and 

pneumophila serogroup 1 eight atypical pneumonia cases) after staying at a hotel. A casecontrol study was conducted and revealed that only exposure to the 

hotel’s indoor spa was a significant risk factor for developing illness. 

Environmental samples did not yield Legionella. However, several 

deficiencies were noted during the investigation, including suboptimal 

water temperatures and stagnation and sediment within the hot-water 

system. Bromine levels in the indoor spa were measured at 0.5 ppm at 

the time of investigation. 

January 2006 Illinois Legionella spp. 43 (1) Forty-three persons became ill (three confirmed Legionnaires’ disease 

and 40 Pontiac fever cases) following a hotel stay. A retrospective 

cohort study was conducted; exposure to the pool area was a 

significant risk factor for developing illness. L. pneumophila and L. 

maceachernii were isolated from water samples of both the pool and 

spa. No disinfectant residual was found in the pool or spa water. 

July 2006 California Shigella sonnei 9 Five families attended a party at a private residence. A fill-and-drain 

pool was filled with tap water with no additional treatment. Shigella 

sonnei was isolated from stool samples submitted by six attendees. 

A retrospective cohort study revealed a significant association 

between pool use and subsequent illness. 
Vol. 57 / SS-9 Surveillance Summaries 35 

State in No. of 

which WBDO cases 

Date occurred Etiologic agent (deaths) Description of WBDO 

Viruses 

May 2006 Wisconsin Norovirus 18 A total of 18 persons developed gastrointestinal illness after using a 

hotel swimming pool and spa; three patients’ stool specimens tested 

positive for norovirus. A case-control study showed a significant 

association between spa and/or pool use and illness. The pool had a 

high bather load, and an ill person had used the pool. Water testing 

records revealed inadequate disinfection during the time of suspected 

exposure. The hotel was advised to close the facilities and either 

hyperchlorinate or drain and refill them. 

Parasites 

June 2005 Florida Cryptosporidium spp. 47 This outbreak affected persons who played in or attended a youth 

sports tournament. Two teams with players who had gastrointestinal 

illness stayed in the same hotel. Although no pool water was tested for 

Cryptosporidium, swimming was the only risk factor significantly 

associated with illness. As a result of the investigation, the hotel was 

advised to keep daily maintenance logs for the swimming area. 

June 2005 New York C. hominis 2,307 An outbreak of gastrointestinal illness was traced to a water park with 

an interactive fountain. Stool samples for 495 of 572 people were 

positive for Cryptosporidium spp. Typing of 147 isolates identified 

them as C. hominis, indicating human contamination. The venue used 

chlorine and rapid sand filtration. Water samples collected from two 

tanks on three dates in mid-August contained C. hominis oocysts. 

C. hominis oocysts were also identified in a water filter and effluent 

from a sewer pump station. Polymerase chain-reaction tests were 

conducted on one water sample from each tank. The samples both 

contained 150 oocysts/L. Investigators determined that multiple factors 

contributed to the outbreak, including an inadequate recirculation 

design in which some water bypassed treatment and filtration as a 

result of the demand of the fountain. 

July 2005 Oregon C. parvum 20 A cohort study was conducted after two confirmed and 15 suspected 

cases of cryptosporidiosis were reported to a local health department. 

Gastrointestinal illness was epidemiologically linked with swimming in 

a pool at a membership club. A child with laboratory-confirmed 

cryptosporidiosis swam in the pool during the days that water 

contamination was suspected to have occurred. Control measures 

were quickly implemented and included hyperchlorination at the 

membership club pool, hyperchlorination of area public pools, and 

posting of signs at multiple pools to discourage swimming by ill 

individuals; prevention messages were disseminated by local media. 

July 2005 Massachusetts Giardia intestinalis 11 An outbreak at an athletic club implicated three outdoor pools (one 

adult pool and two children’s pools) with a shared filtration system. 

All 11 cases were laboratory confirmed. Although not observed, the 

occurrence of a fecal accident was strongly suspected. Records did 

not indicate that disinfectant levels were adjusted or that the pools 

were closed when chlorine readings were below recommended levels 

in early August. A water sample taken during the investigation 

revealed indicator bacteria (coliforms and E. coli) levels above 

allowable limits. 

July 2005 Oklahoma Naegleria fowleri 2 (2) Postmortem clinical specimens from two boys who died several days 

after they became ill indicated that they were infected with N. fowleri. 

Although both of the boys had spent time at a local water park before 

becoming ill, at least one child went swimming in untreated, stagnant 

water near his home before becoming ill. The boys’ homes were not 

far apart from each other. Water samples from a local creek and the 

water park’s spray deck were collected in July and August, respectively. Testing of cultures from both locations did not detect N. fowleri. 

PCR testing of the creek water was also negative. Water testing 

revealed temperatures >95°F (35°C) at both locations. 
36 MMWR September 12, 2008 

State in No. of 

which WBDO cases 

Date occurred Etiologic agent (deaths) Description of WBDO 

August 2005 Ohio C. hominis 523 A large, communitywide cryptosporidiosis outbreak affected 747 

persons in Ohio. Recreational water exposure was associated with 

70% (523/747) of the cases. This outbreak was linked by time and 

proximity to a cryptosporidiosis outbreak in Kentucky. Six pools were 

implicated as a source of exposure to contaminated water. More than 

300 stool samples tested positive for Cryptosporidium. CDC performed additional molecular characterization of the Cryptosporidium 

isolates from one pool filter sand sample from the water park and 

seven clinical stool specimens; the subtype of the isolates of six of the 

stool specimens matched the pool filter sample’s isolate. 

July 2006 California Cryptosporidium spp. 16 This outbreak was initially detected by a laboratory-based active 

cryptosporidiosis surveillance system. Some of the case-patients 

shared a common exposure at a public park with an interactive 

fountain. A 10 L sample from the fountain system contained 137 

oocysts/L and had a chlorine residual of 0.9 ppm. The fountain used a 

sand filtration system that was not designed to remove 

Cryptosporidium spp. and did not have an automated disinfection 

system. Similar public fountains in the area were closed if they had 

inadequate filtration and disinfection. Ill children were restricted from 

attending school and daycare to limit possible person-to-person 

transmission. 

July 2006 Illinois C. hominis 65 Attendees of a private day camp developed gastrointestinal illness that 

was epidemiologically linked to recreational swimming at a private day 

camp pool and at a public outdoor water park. A total of seven 

laboratory-confirmed cases and 58 probable cases were identified. 

PCR detected C. hominis in stool specimens from three patients. An 

inspection of the day camp pool revealed poor water quality, unsanitary pool facilities and an absence of policies intended to prevent 

disease transmission; however, Cryptosporidium was not detected in a 

sample of pool water. Pool water from the water park met state 

guidelines for water quality but tested positive for C. parvum. Fecal 

accidents were reported in both pools. All areas of the water park 

shared one filtration and treatment system; outbreak prevention 

recommendations for the water park included installation of ultraviolet 

(UV) disinfection, as well as education for the staff and the public. 

(Source: CDC. Cryptosporidiosis outbreaks associated with recreational water use—five states, 2006. MMWR 2007; 56:729–32). 

August 2006 Colorado Cryptosporidium spp. 12 Certain persons developed cryptosporidiosis after attending a party at 

a community recreational center with a pool that had UV disinfection in 

addition to chlorination and rapid sand filtration. Swimming, swallowing 

water, and getting water in the mouth were significant risk factors. 

Pool use by diaper-aged children and the use of combined filtration 

systems for the adult and child pools were suspected to have been 

contributing factors in the outbreak. (Source: CDC. Cryptosporidiosis 

outbreaks associated with recreational water use—five states, 2006. 

MMWR 2007;56:729–32). 

Chemicals/Toxins 

June 2005 Michigan Copper sulfate 3 A local resident treated a state lake with copper sulfate to prevent 

swimmer’s itch by controlling snail populations. The pesticide was 

applied without a permit; the quantity was 30 times the labelrecommended amount for algae treatment and three times the labelrecommended amount for snail control. Subsequently, three children 

who spent time near or in the lake developed respiratory symptoms, 

and one was hospitalized. A water test conducted within 1–2 months 

of the pesticide application did not find hazardous levels of copper 

sulfate in the water. 
Vol. 57 / SS-9 Surveillance Summaries 37 

State in No. of 

which WBDO cases 

Date occurred Etiologic agent (deaths) Description of WBDO 

July 2005 Ohio Chlorine gas 19 A chlorine surge at a community pool caused illness in 19 persons. 

The majority of swimmers were children. The predominant symptoms 

were breathing difficulties, cough, sore throat, and eye irritation. The 

recirculation pump failed, but chemical feed pumps continued to feed 

chlorine and acid. When the mechanical pump was restarted, a 

concentrated surge of chlorine gas created by the mixing of the 

concentrated hypochlorous acid and chlorine was introduced into the 

pool. The facility responded to the event by installing an electrical 

interlock that would automatically stop the flow of chemicals if the 

recirculation pump failed. 

Unidentified 

April 2005 Minnesota Suspected chloramines 20 A case-control study was conducted after reports of respiratory and 

ocular symptoms among attendees at a birthday party at a hotel pool. 

Multiple other symptoms were documented, including burning nose 

and throat, nausea, and headache; 12 case-patients sought medical 

care within 1 day of attending the party. Water contact and entering 

the pool enclosure were significantly associated with illness. The 

outbreak investigation determined that the chlorine levels in the pool 

might not have been properly maintained, record-keeping was 

inadequate, showering facilities in the pool area were inadequate, no 

pool operator was on duty, and official bather load was exceeded for 

the pool during the party. 

July 2005 Florida Suspected jellyfish larvae 24 Attendees of a conference reported symptoms such as fever, fatigue, 

headache, chills, and muscle ache. Illness was significantly associated with swimming in the ocean and chlorinated resort pools. No 

clinical specimens were collected because symptoms had resolved 

before the investigation was initiated. Multiple symptoms were 

consistent with exposure to toxins released by minute jellyfish larvae 

(seabather’s eruption). Although weather patterns at the time, as well 

as the month of the outbreak, supported the hypothesis of seabather’s 

eruption, investigators concluded that certain illnesses might have 

occurred as a result of other etiologies. Interview data described poor 

pool water quality and high bather loads. An inspection of the pool 

facilities was conducted as part of the investigation and led to pool 

closure. 

June 2006 Illinois Suspected low pH 9 Swimmers from two classes at a neighborhood swimming pool had 

burning rashes on their bodies after they left the pool. The swimmers 

were ages 4–8 years. The instructor, who was in the water for a total 

of 80 minutes, reported a similar rash on his arms. Testing indicated 

that the pool water had a low pH. The exact pH could not be determined; the lower limit for the test strip was seven. The problem was 

traced back to the automatic sensing unit for feeding acid, which was 

not working correctly. 

December 2006 Nebraska Suspected chloramines 24 A child attending a family event at a motel swam for 3 hours in the 

indoor pool, during which time he developed respiratory symptoms. He 

was hospitalized overnight with severe chemical epiglottitis and 

laryngotracheobronchitis. A follow-up investigation identified 24 casepatients who had developed ocular and/or respiratory symptoms after 

being in or near the pool. The state health department inspected the 

pool and closed it as a result of multiple state health code violations. 

Pool water pH was 3.95 (acceptable range: 7.2–7.8); the free chlorine 

level was 0.8 ppm (acceptable range: 2–10 ppm) and the combined 

chlorine level was 4.2 ppm (acceptable limit: <0.5 ppm). Pool records 

indicated that water quality violations had occurred frequently during a 

26-day period before the outbreak. Chloramine levels might have been 

higher on the day that the child became ill because of inadequate 

ventilation; the only ceiling exhaust fan was turned off, and all of the 

nearby windows were closed. Although the motel was licensed by the 

state of Nebraska, it was a nonmunicipal public pool and, therefore, 

pool operators were not required to undergo training and certification. 

(Source: CDC. Ocular and respiratory illness associated with an 

indoor swimming pool—Nebraska, 2006. MMWR 2007;56:929–32). 
38 MMWR September 12, 2008 

State in No. of 

which WBDO cases 

Date occurred Etiologic agent (deaths) Description of WBDO 

Vibrio infections 

August 2005 Louisiana Vibrio vulnificus 1 (1) A man aged 60 years waded for 3 days in flood waters after Hurricane 

Katrina in New Orleans, Louisiana, and arrived in Texas during the 

end of August 2005. His medical history included stroke, hypertension, 

and alcohol abuse. The day after he arrived in Texas, he went to an 

emergency department; he had ankle wounds and diarrhea. He was 

released after treatment but was admitted to the hospital 1 day later 

when Vibrio vulnificus was positively identified from a blood culture. 

He died in the hospital the next day. (Source: CDC. Vibrio illnesses 

after Hurricane Katrina—multiple states, August–September 2005. 

MMWR 2005;54:928–31). 

August 2005 Mississippi V. parahaemolyticus 1 (1) A man aged 61 years died shortly after seeking medical treatment for 

V. parahaemolyticus infection; he had hypothermia and multiple 

second-and third–degree abrasions on his body after exposure to 

Hurricane Katrina flood waters. The patient was also known to have 

human immunodeficiency virus infection, coronary artery disease, and 

hyperlipidemia. (Source: CDC. Vibrio illnesses after Hurricane 

Katrina—multiple states, August–September 2005. MMWR 

2005;54:928–31). 
Vol. 57 / SS-9 Surveillance Summaries 39 

Surveillance for Waterborne Disease and Outbreaks Associated 

with Drinking Water and Water not Intended for Drinking — 

United States, 2005–2006 

Jonathan Yoder MSW, MPH1
 

Virginia Roberts, MSPH1,2
 

Gunther F. Craun, MPH3
 

Vincent Hill, PhD, PE1
 

Lauri Hicks, DO4
 

Nicole T. Alexander, MPH4
 

Vince Radke MPH5
 

Rebecca L. Calderon, PhD6
 

Michele C. Hlavsa, MPH1
 

Michael J. Beach, PhD1
 

Sharon L. Roy, MD1
 

1Division of Parasitic Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Disease, CDC
 

2Atlanta Research and Education Foundation
 

3Gunther F. Craun and Associates, Staunton, Virginia
 4Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, CDC
 5Division of Emergency and Environmental Health Services, National Center for Environmental Health, CDC
 6U.S. Environmental Protection Agency, Research Triangle Park, North Carolina
 

Abstract

Problem/Condition: Since 1971, CDC, the U.S. Environmental Protection Agency (EPA), and the Council of State 

and Territorial Epidemiologists have maintained a collaborative Waterborne Disease and Outbreak Surveillance System (WBDOSS) for collecting and reporting data related to occurrences and causes of waterborne-disease outbreaks 

(WBDOs) and cases of waterborne disease. This surveillance system is the primary source of data concerning the scope 

and effects of waterborne disease in the United States. 

Reporting Period: Data presented summarize 28 WBDOs that occurred during January 2005–December 2006 and 

four previously unreported WBDOs that occurred during 1979–2002. 

Description of System: The surveillance system includes data on WBDOs associated with recreational water, drinking 

water, water not intended for drinking (WNID) (excluding recreational water), and water use of unknown intent. 

Public health departments in the states, territories, localities, and Freely Associated States (FAS) (i.e., the Republic of 

the Marshall Islands, the Federated States of Micronesia, and the Republic of Palau, formerly parts of the U.S.-administered Trust Territory of the Pacific Islands) are primarily responsible for detecting and investigating WBDOs and 

voluntarily reporting them to CDC by a standard form. Only cases and outbreaks associated with drinking water, 

WNID (excluding recreational water), and water of unknown intent (WUI) are summarized in this report. Cases and 

outbreaks associated with recreational water are reported in a separate Surveillance Summary. 

Results: Fourteen states reported 28 WBDOs that occurred during 2005–2006: a total of 20 were associated with 

drinking water, six were associated with WNID, and two were associated with WUI. The 20 drinking water-associated 

WBDOs caused illness among an estimated 612 persons and were linked to four deaths. Etiologic agents were identified in 18 (90.0%) of the drinking water-associated WBDOs. 

Among the 18 WBDOs with identified pathogens, 12 (66.7%) were associated with bacteria, three (16.7%) with 

viruses, two (11.1%) with parasites, and one (5.6%) mixed WBDO with both bacteria and viruses. In both WBDOs 

where the etiology was not determined, norovirus was the suspected etiology. 

Of the 20 drinking water WBDOs, 10 (50) were outbreaks of acute respiratory illness (ARI), nine (45%) were 

outbreaks of acute gastrointestinal illness (AGI), and one (5.0%) was an outbreak of hepatitis. All WBDOs of ARI 

were caused by Legionella, and this is the first reporting 

period in which the proportion of ARI WBDOs has sur- Corresponding author: Jonathan S. Yoder, MSW, MPH, Division of Parasitic 

Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases,
 passed that of AGI WBDOs since the reporting of 

4770 Buford Hwy., NE, MS F-22, Atlanta, GA 30341. Telephone: 770-488- Legionella WBDOs was initiated in 2001.
 

3602; Fax: 770-488-7761. E-mail: jey9@cdc.gov.
 
40	 MMWR September 12, 2008 

A total of 23 deficiencies were cited in the 20 WBDOs associated with drinking water: 12 (52.2%) deficiencies fell 

under the classification NWU/POU (deficiencies occurred at points not under the jurisdiction of a water utility or at 

the point-of-use), 10 (43.5%) deficiencies fell under the classification SWTDs (contamination at or in the source 

water, treatment facility, or distribution system), and for one (4.3%) deficiency, classification was unknown. Among 

the 12 NWU/POU deficiencies, 10 (83.3%) involved Legionella spp. in the drinking water system. The most frequently cited SWTD deficiencies were associated with a treatment deficiency (n = four [40.0%]) and untreated ground 

water (n = four [40.0%]). Three of the four WBDOs with treatment deficiencies used ground water sources. 

Interpretation: Approximately half (52.2%) of the drinking water deficiencies occurred outside the jurisdiction of a 

water utility. The majority of these WBDOs were associated with Legionella spp, which suggests that increased attention should be targeted towards reducing illness risks associated with Legionella spp. Nearly all of WBDOs associated 

with SWTD deficiencies occurred in systems using ground water. EPA’s new Ground Water Rule might prevent similar 

outbreaks in the future in public water systems. 

Public Health Actions: CDC and EPA use surveillance data to identify the types of water systems, deficiencies, and 

etiologic agents associated with WBDOs and to evaluate the adequacy of current technologies and practices for providing safe drinking water. Surveillance data also are used to establish research priorities, which can lead to improved 

water-quality regulation development. The majority of drinking water deficiencies are now associated with contamination at points outside the jurisdiction of public water systems (e.g., regrowth of Legionella spp. in hot water systems) 

and water contamination that might not be regulated by EPA (e.g., contamination of tap water at the POU). Improved 

education of consumers and plumbers might help address these risk factors. 

Introduction	 

Statistical data on waterborne-disease outbreaks (WBDOs) 

in the United States have been collected since 1920. Researchers 

reported these statistics during 1920–36 (1), 1938–1945 (2),
 

1946–1960 (3), and 1961–1970 (4). Since 1971, CDC, the 

U.S. Environmental Protection Agency (EPA), and the Council of State and Territorial Epidemiologists (CSTE) have maintained a collaborative Waterborne Disease and Outbreak 

Surveillance System (WBDOSS), which tracks the occurrences 

and causes of WBDOs and cases of disease associated with 

drinking water. The history of WBDO surveillance in the 

United States is summarized in the 2003–2004 WBDOSS 

Surveillance Summary (5). The 2005–2006 Surveillance Summary presents data on 28 WBDOs reported by public health 

departments in the states, territories, and localities that 

occurred during January 2005–December 2006, and four previously unreported WBDOs that occurred during 1979–2002. 

However, the statistics in this report represent only a portion 

of the burden of illness associated with water exposure. They 

do not include endemic waterborne-disease cases (sporadic 

cases not known to be associated with a WBDO), WBDOs 

associated with recreational water use, or reliable estimates of 

the number of unrecognized WBDOs.	 

Background 

U.S. Environmental Protection Agency 

Drinking Water Regulations 

The majority of WBDOs reported in this Surveillance
 

Summary occurred in public drinking water systems. The Safe 

Drinking Water Act (SDWA) of 1974 and its subsequent 1986 

and 1996 amendments (Table 1) authorize EPA to set 

national standards to protect public drinking water and its 

sources against naturally occurring or man-made contaminants 

(6–8). EPA has set health-based standards for approximately 

90 chemical, microbiologic, radiologic, and physical contaminants in drinking water. Standards include a maximum contaminant level* (amount of a contaminant allowed in water 

delivered to the consumer) or treatment technique (required 

procedure or level of technological performance) that apply 

to systems providing water to at least 15 service connections 

or 25 persons for at least 60 days in a year (Public Water Systems). EPA also has recommended guidelines (Secondary 

Drinking Water Regulations), for water contaminants that 

primarily affect the aesthetic qualities of drinking water (e.g., 

taste, odor, and staining of laundry) that states may choose to 

adopt and enforce. EPA regulations and guidelines do not 

apply to private, individual water supplies (Figure 1); however, certain states set standards for individual water supplies. 

* Additional terms have been defined (Appendix A, Glossary of Definitions). 
Vol. 57 / SS-9 Surveillance Summaries 41 

TABLE 1. U.S. Environmental Protection Agency regulations 

regarding drinking water, by year enacted — United States, 

1974–2006 

Regulation Year 

Safe Drinking Water Act (SDWA) 1974 

Interim Primary Drinking Water Standards 1975 

National Primary Drinking Water Standards 1985 

SDWA Amendments 1986 

Surface Water Treatment Rule (SWTR) 1989 

Total Coliform Rule 1989 

Lead and Copper Regulations 1990 

SDWA Amendments 1996 

Information Collection Rule 1996 

Interim Enhanced SWTR 1998 

Disinfectants and Disinfection By-Products (D-DBPs) Regulation 1998 

Contaminant Candidate List 1998 

Unregulated Contaminant Monitoring Regulations 1999 

Lead and Copper Rule — action levels 2000 

Filter Backwash Recycling Rule 2001 

Long Term 1 Enhanced SWTR 2002 

Unregulated Contaminant Monitoring Regulations 2002 

Drinking Water Contaminant Candidate List 2 2005 

Long Term 2 Enhanced SWTR 2006 

Stage 2 D-DBP Rule 2006 

Ground Water Rule 2006 

Public and individual water system types and subtypes have 

been defined (Appendix A, Glossary of Definitions). 

Standards by which microbial contamination is regulated 

include the Total Coliform Rule (TCR) (9,10), Ground 

Water Rule (GWR) (11,12), Wellhead Protection Program 

(11), Surface Water Treatment Rule (SWTR) (13), Interim 

Enhanced SWTR (14), Long Term 1 Enhanced SWTR (15), 

Long Term 2 Enhanced SWTR (16–18), Stage 2 Disinfectants and Disinfection By-products Rule (16, 17), and Filter 

Backwash Recycling Rule (19). EPA’s lead, copper, and 

arsenic rules prescribe action levels at which a system operator 

must take corrective steps (20,21). In addition, EPA is 

required to publish periodically a list of contaminants that 

might need to be regulated (22,23) and establish criteria for a 

program to monitor unregulated contaminants (24–27). EPA 

decides whether or not to regulate contaminants on the list 

based on projected adverse health effects from the contaminant, an assessment of the extent of occurrence of the contaminant in drinking water, and the potential for reducing 

risks to health. Instead of a regulation, EPA can issue guidance or a health advisory. All of these requirements have been 

described in previous Surveillance Summaries (5,28). In 2007, 

EPA established an advisory committee to provide recommendations on revisions to the TCR and on information needed 

to better understand the public health risks associated with 

the degradation of water quality in pipes, storage tanks, and 

other appurtenances used to distribute drinking water to consumers (29). 

Methods 

Data Sources 

Public health departments in the states, territories, localities, 

and FAS have primary responsibility for detecting and investigating WBDOs, which they report voluntarily to CDC using a 

standard form (CDC form 52.12, available at http://www. 

cdc.gov/healthyswimming/downloads/cdc_5212_ 

waterborne.pdf). The form solicits data on characteristics of 

WBDO (e.g., number of cases, time, and location); results 

from epidemiologic studies; results from clinical specimen and 

water sample testing; and other factors potentially contributing to WBDO (e.g., environmental conditions, disinfection 

deficiencies, and filtration problems). CDC annually requests 

reports of WBDOs and single cases of certain waterborne diseases, as specified in the definitions in the next section, from 

state, territorial, and FAS epidemiologists or persons designated as WBDO surveillance coordinators and obtains additional information regarding water quality and water treatment 

as needed. In certain instances, information on WBDOs and 

cases is solicited from other CDC surveillance systems and 

confirmed with the state or locality for inclusion in WBDOSS 

and/or Surveillance Summary, which is illustrated in more 

detail in a separate Surveillance Summary (30). Numerical and 

text data are abstracted from WBDO report form and supporting documents and entered into a database for analysis. 

Although reports of WBDOs are collected through WBDOSS, 

the cases and outbreaks associated with drinking water, water 

not intended for drinking (WNID), and water of unknown 

intent (WUI) are analyzed and published separately from the 

cases and outbreaks associated with recreational water (30). 

Definitions 

WBDOSS collects data on both outbreaks and individual 

cases of waterborne disease. Two criteria must be met for an 

event to be defined as a waterborne-disease outbreak associated with drinking water, WNID (excluding recreational 

water), or WUI. First, two or more persons must be epidemiologically linked by location of exposure to water, and by 

time, and characteristics of illness. Second, the epidemiologic 

evidence must implicate water as the probable source of illness. 

In addition to WBDOs, single cases of laboratory-confirmed 

primary amebic meningoencephalitis (PAM) as a result of 

Naegleria fowleri infection with a known water exposure and single 

cases of chemical/toxin poisoning, if water-quality data indicate 

contamination by the chemical/toxin, are also reported in 

WBDOSS. All single cases are discussed separately from WBDOs. 

Single cases of legionellosis are reported elsewhere (31). 
 

42 MMWR September 12, 2008 

FIGURE 1. Types of drinking water systems — United States 

Drinking Water Systems 

Public Water Systems 

Public or private ownership 

(subject to EPA* regulations) 

Individual Water Systems 

(if regulated, state or local regulations) 

Noncommunity Community Use of nonpublic sources 

Transient (e.g., gas stations, parks, resorts, 

campgrounds, restaurants, and motels 

with their own water systems) 

Nontransient (e.g., schools, factories, 

office buildings, and hospitals 

with their own water systems) 

Privately owned home or farm wells, 

springs, or surface water sources 

Streams, ponds, or shallow wells 

not intended for drinking 

Bottled water (commercially bottled water is 

regulated by FDA† ; persons might also 

fill their own containers) § 

* U.S. Environmental Protection Agency. 

†Food and Drug Administration.
 

§ In certain instances, bottled water is used in lieu of a community supply or by noncommunity systems.
 

Reported outbreaks associated with contaminated drinking 

water; commercially bottled water, ice, or beverages made with 

contaminated water; and water contaminated by malfunctions 

in equipment/devices in which water is used or distributed 

(e.g., beverages contaminated by plumbing failures in drink 

mix/soda machines) are classified as WBDOs. Tabulation of 

WBDOs is based on location of water exposure, not on state 

of residence of the ill persons. WBDOs associated with cruise 

ships are not summarized in this report. 

Of the approximately 155,693 public water systems in the 

United States, 52,110 (33.5%) are community systems and 

103,583 (66.5%) are noncommunity systems, including 

84,744 transient systems and 18,839 nontransient systems. 

Community systems serve 286.5 million persons, and only 

8% of these systems provide water to 82% of the U.S. population through large municipal water systems (32). Noncommunity, nontransient systems provide water to 6.3 million 

persons, and noncommunity, transient systems provide water 

to 13.8 million persons (by definition, these populations also 

use another type of water system at their residences, except for 

the limited number of permanent residents of nontransient systems) (32). Although the majority of public water systems (91%) 

are supplied by ground water, more persons (68%) are supplied 

year-round by community water systems that use surface water 

(32). Approximately 15.0% of the U.S. population relies on 

individual water systems that are privately owned (33). 

WBDOs associated with commercially bottled water are 

classified separately from the water systems described in this 

Surveillance Summary. Separating piped from nonpiped water 

distinguishes between drinking water systems regulated by EPA 

(community and noncommunity) and the Food and Drug 

Administration (FDA) (bottled). 

The purpose of WBDOSS is not only to evaluate the relation between water and reported disease outbreaks and cases, 

but also to identify system breakdowns, operator errors, other 

engineering-related activities, and environmental situations 

that lead to outbreaks. To understand the circumstances and 

system breakdowns that lead to illness, each WBDO is classified as having one or more deficiencies (Table 2). 

Waterborne Disease and Outbreak 

Strength of Evidence Classification 

All WBDOs reported to the surveillance system have been 

classified according to the strength of the evidence implicating water as the vehicle of transmission (Table 3). The classification scheme (i.e., Classes I–IV) is based on the 

epidemiologic and water-quality data provided with WBDO 

report form. Although WBDOs without water-quality data 

were included in this report, reports that lacked epidemiologic data, linking the outbreak to water, have been excluded. 

A classification of I indicates that adequate epidemiologic 

and water-quality data were reported. However, this classification does not necessarily imply that the investigation was 

conducted optimally nor does a classification of II, III, or IV 

imply that the investigation was inadequate or incomplete. 
Vol. 57 / SS-9 Surveillance Summaries 43 

TABLE 2. Deficiency classification for drinking water, water not intended for drinking (excluding recreational water), and water of 

unknown intent 

Deficiency 

Contamination of water at/in the water source, treatment facility, or distribution system (SWTD)* 

1: Untreated surface water intended for drinking 

2: Untreated ground water intended for drinking 

3: Treatment deficiency (e.g., temporary interruption of disinfection, chronically inadequate disinfection, inadequate or no filtration) 

4: Distribution system deficiency, including storage (e.g., cross-connection, backflow, contamination of water mains during construction or repair) 

13: Current treatment processes not expected to remove a chemical contaminant (e.g., pesticide contamination of groundwater treated with disinfection only) 

A: Surface water 

B: Ground water 

Contamination of water at points not under the jurisdiction of a water utility or at the point of use (NWU/POU)† 

5: Legionella spp. in water system 

A: Water intended for drinking 

B: Water not intended for drinking (excluding recreational water) 

C:Water of unknown intent 

6: Plumbing system deficiency after the water meter or property line (e.g., cross-connection, backflow, corrosion products) 

7: Deficiency in building/home-specific water treatment after the water meter or property line 

8: Deficiency or contamination of equipment using or distributing water (e.g., drink-mix machines) 

9: Contamination or treatment deficiency during commercial bottling 

10: Contamination during shipping, hauling, or storage 

A: Water intended for drinking – Tap water 

B: Water intended for drinking – Commercially bottled water 

11: Contamination at point-of-use 

A: Tap 

B: Hose 

C:Commercially bottled water 

D:Container, bottle, or pitcher 

E: Unknown 

12: Drinking or contact with water not intended for drinking (excluding recreational water) 

Unknown/Insufficient Information 

99: Unknown/Insufficient information 

A: Water intended for drinking – Tap water 

B: Water intended for drinking – Commercially bottled water 

C:Water not intended for drinking (excluding recreational water) 

D:Water of unknown intent 

* Contamination of water and deficiencies occurring in the drinking water system at/in the water source, treatment facility, or distribution system of pipes 

and storage facilities. For a community water system, the distribution system refers to the pipes and storage infrastructure under the jurisdiction of the 

water utility before the water meter or property line (if the system is not metered). For noncommunity and nonpublic individual water systems, the 

distribution system refers to the pipes and storage infrastructure before entry into a building or house (e.g., in a service line leading to a house or 

building). 

†Contamination of drinking water and deficiencies occurring in plumbing and pipes that are not part of the distribution system or at other points outside 

the jurisdiction of a water utility. For community systems, this means after the water meter or property line (if the system is not metered), and for 

noncommunity and nonpublic systems, this means within the building or house (e.g., in the plumbing inside a house or building). This category also 

includes contamination during shipping or hauling, during storage other than in the distribution system, and at point-of-use). 

WBDOs and their resulting investigations occur under dif- Deficiencies 

ferent circumstances, and not all WBDOs can be rigorously One deficiency, 13, has been added to the deficiency classifi­ investigated. In addition, WBDOs that affect few persons are cation table (Table 2). This deficiency will allow for the classifi­ more likely to receive a classification of III or IV because of cation of chemical contamination of source water when the 

the limited sample size available for epidemiologic analysis. existing treatment provided for the system is not designed to 

remove that chemical contamination. WBDOs associated with 

Changes in the 2005–2006 Surveillance chemical contamination of untreated source water will 

Summary continue to be reported under deficiencies 1 or 2 as appropriate. 

Definitions and deficiencies in this report have been modified to Definition 

better reflect the epidemiology of WBDOs and capture the scope The definition of a waterborne disease outbreak (WBDO) of water-related disease. This section highlights those changes. has been modified to include only water exposure in which 

more than two persons become ill. Single cases of PAM and 
44 MMWR September 12, 2008 

TABLE 3. Classification of investigations of waterborne disease and outbreaks based on strength of evidence implicating water 

as a vehicle of transmission — United States, 2005–2006 

Class Epidemiologic data Water-quality data 

I Adequate Provided and adequate 

Data provided concerning exposed and unexposed persons, Laboratory data or historical information (e.g., reports of a 

with relative risk or odds ratio >2 or p<0.05 chlorinator malfunction, a water main break, no detectable 

free-chlorine residual, or the presence of coliforms in the water) 

II Adequate Not provided or inadequate (e.g., laboratory testing of water not

 conducted and no historical information) 

III Provided but limited Provided and adequate 

Epidemiologic data provided that did not meet the criteria for 

Class I, or claim made that ill persons had no exposures in 

common besides water but no data provided 

IV Provided but limited Not provided or inadequate 

illnesses caused by exposure to chemically-contaminated 

water will continue to be included in WBDOSS but will not 

be classified or analyzed as outbreaks. This change will provide a consistent outbreak definition of two or more persons 

epidemiologically linked by location of exposure to water, and 

by time, and characteristics of illness. 

Results 

During 2005–2006, a total of 14 states reported 28 WBDOs 

(i.e., 13 for 2005 and 15 for 2006). These WBDOs were 

associated with drinking water (n = 20), WNID (n = six), and 

WUI (n = two) and are tabulated by year and state (Tables 

4–6). Four previously unreported WBDOs that occurred during 1979–2002 also were reported (Table 7). 

Waterborne Disease and Outbreaks 

Associated with Drinking Water 

The 20 drinking water-associated WBDOs (i.e., eight in 

2005 and 12 in 2006) were reported by 11 states (Figure 2). 

Multiple etiologic agents were implicated (Figure 3), and 

WBDOs occurred throughout the year (Figure 4). Selected 

descriptions of WBDOs are presented (Appendix B). 

The 20 drinking water-associated WBDOs reported during 2005–2006 caused illness among at least 612 persons and 

resulted in four deaths. The median number of persons 

affected in a WBDO was 10 (range: two–148). One WBDO 

was associated with hepatitis A. The remaining WBDOs were 

associated with either acute gastrointestinal illness (AGI) or 

acute respiratory illness (ARI). All ARI outbreaks were associated with exposure to Legionella spp. (Figure 5). 

Four (20.0%) of the 20 drinking water-associated WBDOs 

were given a strength of evidence Class I ranking on the basis 

of epidemiologic and water-quality data; two (10.0%) were 

ranked as Class II; 13 (65.0%) were ranked as Class III; 

and one (5.0%) was ranked as Class IV. Drinking waterassociated WBDOs are tabulated by etiologic agent and type 

of water system (Table 8), etiologic agent and type of water 

source (Table 9), type of deficiency and type of water system 

(Table 10), type of deficiency and type of water source 

(Table 11), predominant illness and type of water system 

(Table 12), and predominant illness and type of water source 

(Table 13). WBDOs were included (Tables 8–13) only if the 

type of deficiency might be relevant in the cause of WBDO 

(e.g., understanding the source of raw untreated water is 

unlikely to be important for a legionellosis outbreak associated with a building plumbing system). 

Etiologic Agents 

Of the 20 drinking water-associated WBDOs, 12 (60.0%) 

were caused by bacteria, three (15.0%) were caused by 

viruses, two (10.0%) were caused by parasites, and one (5.0%) 

was caused by more than one etiologic agent type. Two (10.0%) 

were of unknown etiology (Figure 6). 

Bacteria. Twelve WBDOs affecting 135 persons were 

attributed to bacterial infections: 10 outbreaks caused by 

Legionella; one outbreak caused by Campylobacter; and one 

outbreak (Oregon, 2005) in which persons had multiple stool 

specimens that tested positive for C. jejuni, Escherichia 

O157:H7, and E. coli O145. Illnesses from these 12 WBDOs 

resulted in four deaths, all of which were associated with 

Legionella spp. 

Viruses. Three WBDOs affecting 212 persons were attributed to viral infections: two outbreaks caused by norovirus 

G1, and one outbreak caused by hepatitis A. No deaths were 

reported. 

Parasites. Two WBDOs affecting 51 persons were attributed to parasites: one outbreak caused by Giardia intestinalis 

and one outbreak caused by Cryptosporidium. No deaths were 

reported. 
Vol. 57 / SS-9 Surveillance Summaries 45 

TABLE 4. Waterborne-disease outbreaks associated with drinking water (n = eight), by state — United States, 2005 

State Month Class Etiologic agent 

Predominant 

illness* 

No. of cases 

(deaths)† 

(n = 180) 

Type of 

system§ Deficiency¶ 

Water 

source Setting 

California 

Florida 

New York 

New York 

New York 

Ohio 

Oregon 

Pennsylvania 

Aug 

Nov 

Dec 

Dec 

Dec 

Aug 

May 

Nov 

II 

IV 

III 

III 

III 

I 

III 

III 

Giardia intestinalis 

Legionella pneumophila 

 serogroup 1

L. pneumophila serogroup 6 

L. pneumophila serogroup 6 

L. pneumophila serogroup 1 

Unidentified§§ 

Escherichia coli O157:H7 

Campylobacter jejuni, 

and E. coli O145*** 

L. pneumophila serogroup 1 

AGI 

ARI 

ARI 

ARI 

ARI 

AGI 

AGI 

ARI 

41 

2 

2 

8 

4 (1) 

59 

60 

4 

Unknown 

Unknown** 

Com 

Com 

Com 

Ncom 

Ncom 

Ncom 

11D 

5A 

5A 

5A 

5A 

3 

3 

5A 

Unknown 

Unknown†† 

Lake†† 

Lake†† 

Lake†† 

Spring 

River 

Unknown†† 

Gym 

Senior housing

 center 

Hospital 

Hospital 

Hospital 

Restaurant¶¶ 

Camp 

Long-term–care

 facility 

* AGI: acute gastrointestinal illness; and ARI: acute respiratory illness. 

† Deaths are indicated in parentheses if they occurred. 

§ Com: community; and Ncom: noncommunity. Community and noncommunity water systems are public water systems that have >15 service connections or serve an average of >25 residents for >60 days/year. A community water system serves year-round residents of a community, subdivision, or 

mobile home park. A noncommunity water system serves an institution, industry, camp, park, hotel, or business and can be nontransient or transient. 

Nontransient systems serve >25 of the same persons for >6 months of the year but not year-round (e.g., factories and schools), whereas transient 

systems provide water to places in which persons do not remain for long periods (e.g., restaurants, highway rest stations, and parks). Individual water 

systems are small systems not owned or operated by a water utility that have <15 connections or serve <25 persons. 

¶ Deficiency classification for drinking water, water not intended for drinking (excluding recreational water), and water of unknown intent (see Table 2). 

** Senior Housing center is served by a community system with a ground water source; however, case-patients traveled together to other cities where 

exposure might have occurred. †† Transmission of Legionella thought to be a result of building-specific factors and not related to water source. §§ Etiology unidentified; norovirus suspected based upon incubation period, symptoms, and duration of illness. ¶¶ Private residence was licensed to serve food. 

*** Nine persons had stool specimens that tested positive for E. coli O157:H7, three persons had stool specimens that tested positive for C. jejuni, two 

persons had stool specimens that tested positive for E. coli O145, and three persons had stool specimens that tested positive for both E. coli O157:H7 

and C. jejuni. 

Mixed agent types. One WBDO was attributed to more 

than one type of etiologic agent; no deaths were reported. 

This outbreak affected 139 persons and involved two viruses 

(norovirus G1 and norovirus G2) and one bacterium 

(C. jejuni) (34). 

Unidentified etiologic agents. Two WBDOs involving AGI 

of unidentified etiology affected 75 persons; no deaths were 

reported. No viral testing was attempted in one of the outbreaks (Ohio 2005). In the other outbreak (New York 2006), 

norovirus, enterovirus, and rotavirus were isolated from 

water samples. In both of the outbreaks, norovirus was the 

suspected etiology on the basis of incubation period, symptoms, and duration of illness. 

Deficiencies 

Twenty-three deficiencies were cited in the 20 drinking 

water-associated WBDOs. Ten (43.5%) deficiencies involved 

the source water, treatment facility, or distribution system 

(SWTD) and 12 (52.2%) deficiencies occurred at points not 

under the jurisdiction of a water utility or at the point-of-use 

(NWU/POU). One WBDO (4.3%) had an unknown deficiency (Figure 7; Table 14). 

Deficiencies 1–4 and 13: Contamination 

of Water at/in the Water Source, Treatment 

Facility, or Distribution System 

Eight WBDOs were given a deficiency classification of 

1–4. Three (37.5%) of these WBDOs were associated with 

viruses, two (25.0%) were associated with bacteria, two 

(25.0%) were associated with unidentified etiologic agents, 

and one (12.5%) was associated with mixed agent types. 

Water-quality data. All eight WBDOs with a deficiency 

classification of 1–4 had water-quality data (e.g., laboratory 

data regarding the presence of coliform bacteria, pathogens, 

or chemical/toxin contaminants; or historical data [e.g., levels of disinfectants]). Positive total or fecal coliform results 

from the implicated water were reported for four (66.7%) of 

the six WBDOs with confirmed infectious etiologies. In two 

WBDOs caused by norovirus G1 and hepatitis A virus, the 

implicated pathogens were isolated from water in addition to 

fecal coliforms and E. coli.

Water systems. Five (62.5%) of eight WBDOs with deficiencies 1–4 involved noncommunity water systems, two

(25.0%) involved individual water systems, and one (12.5%) 

involved a community water system (Tables 8, 10, and 12; 

Figure 6). Among the five outbreaks involving noncommu­
46 MMWR September 12, 2008 

TABLE 5. Waterborne-disease outbreaks associated with drinking water (n = 12), by state — United States, 2006 

State Month Class Etiologic agent 

Predominant 

illness* 

No. of cases 

(deaths)† 

(n = 432) 

Type of 

system§ Deficiency¶ 

Water 

source Setting 

Indiana 

Maryland 

North Carolina 

New York 

New York 

New York 

Ohio 

Ohio 

Oregon 

Pennsylvania 

Texas 

Wyoming 

Feb 

Jul 

Jul 

Aug 

Jun 

Jan 

Sep 

Aug 

Dec 

Apr 

Apr 

Jun 

I 

III 

I 

III 

III 

III 

II 

III 

III 

III 

III 

I 

Campylobacter 

Norovirus G1 

Hepatitis A 

Unidentified** 

Legionella†† 

L. pneumophila serogroup 3 

Cryptosporidium 

L. pneumophila serogroup 1 

Norovirus G1 

L. pneumophila serogroup 1 

L. pneumophila†† 

Norovirus G1, C. jejuni, 

Norovirus G2¶¶ 

AGI 

AGI 

Hep 

AGI 

ARI 

ARI 

AGI 

ARI 

AGI 

ARI 

ARI 

AGI 

32 

148 

16 

16 

4 

2 

10 

3 

48 

4 

10 (3) 

139 

Com 

Ncom 

Ind 

Ind 

Com 

Com 

Com 

Com 

Ncom 

Ncom 

Com 

Ncom 

3, 4 

3, 4, 11B 

2 

2 

5A 

5A 

99A 

5A 

2 

5A 

5A 

2 

Well 

Well 

Spring 

Well 

Lake§§ 

Reservoir§§ 

Well 

Lake§§ 

Well 

Well§§ 

Unknown§§ 

Well 

Community 

Camp 

Private residence 

Bed and 

Breakfast 

Hospital 

Hospital 

Church 

Hospital 

Restaurant 

Hotel 

Hospital 

Camp 

* AGI: acute gastrointestinal illness; ARI: acute respiratory illness; and Hep: viral hepatitis. 

† Deaths are indicated in parentheses if they occurred. 

§ Com: community; Ncom: noncommunity; and Ind: individual. Community and noncommunity water systems are public water systems that have >15 

service connections or serve an average of >25 residents for >60 days/year. A community water system serves year-round residents of a community, 

subdivision, or mobile home park. A noncommunity water system serves an institution, industry, camp, park, hotel, or business and can be nontransient 

or transient. Nontransient systems serve >25 of the same persons for >6 months of the year but not year-round (e.g., factories and schools), whereas 

transient systems provide water to places in which persons do not remain for long periods (e.g., restaurants, highway rest stations, and parks). Individual water systems are small systems not owned or operated by a water utility that have <15 connections or serve <25 persons. 

¶ Deficiency classification for drinking water, water not intended for drinking (excluding recreational water), and water of unknown intent (see Table 2). 

** Etiology unidentified; norovirus suspected based upon incubation period, symptoms, and duration of illness. Norovirus, enterovirus, and rotavirus were 

isolated from the well. 

†† Environmental testing detected L. pneumophila serogroup 1, L. pneumophila other than serogroup 1, and non-pneumophila Legionella species.
 §§ Transmission of Legionella thought to be as a result of building-specific factors and not related to water source.
 

¶¶ Eight persons had stool specimens that tested positive for norovirus G1, six persons had stool specimens that tested positive for C. jejuni, and three
 

persons had stool specimens that tested positive for norovirus G2. Source: CDC. Gastroenteritis among attendees at a summer camp—Wyoming, 

June–July 2006. MMWR 2007;56:368–70. 

TABLE 6. Waterborne-disease outbreaks associated with water not intended for drinking (WNID) (excluding recreational water) 

and water of unknown intent (WUI) (n = eight) — United States, 2005–2006 

State 

Water 

type 

Month/ 

Year Class Etiologic agent 

Predominant 

illness* 

No. of cases 

(deaths)† 

(n = 96) Deficiency§ 

Primary 

water 

exposure Setting 

California 

Colorado 

New York 

New York 

New York 

Pennsylvania 

South Dakota 

Tennessee 

WNID 

WNID 

WNID 

WNID 

WNID 

WUI 

WNID 

WUI 

Jul 2005 

May 2006 

Jul 2005 

Jan 2006 

Aug 2006 

Jul 2005 

May 2005 

Aug 2005 

IV 

II 

III 

III 

III 

IV 

I 

II 

Giardia intestinalis 

G. intestinalis 

Legionella pneumophila 

 serogroup 1 

L. pneumophila serogroup 1 

L. pneumophila serogroup 1 

L. pneumophila serogroup 1 

L. pneumophila serogroup 1¶ 

Escherichia coli O157:H7 

AGI 

AGI 

ARI 

ARI 

ARI 

ARI 

ARI 

AGI 

3 

6 

22 (3) 

2 

28 (3) 

3 

18 (1) 

14 

12 

12 

5B 

5B 

5B 

5C 

5B 

99D 

Canal 

River 

Cooling tower 

Cooling tower 

Cooling tower 

Unknown 

Decorative 

 fountain 

Unknown** 

Private

 residence 

Wilderness 

Hospital

Hospital 

Nursing home 

Hotel 

Restaurant 

Sports camp 

* AGI: acute gastrointestinal illness; and ARI: acute respiratory illness. 

† Deaths are indicated in parentheses if they occurred.
 

§ Deficiency classification for drinking water, water not intended for drinking (excluding recreational water), and water of unknown intent (see Table 2).
 

¶ Source: O’Loughlin RE, Kightlinger L, Werpy MC, et al. Restaurant outbreak of Legionnaires’ disease associated with a decorative fountain: an
 

environmental and case control study. BMC Infect Dis 2007; 7:93. 

** Illnesses were associated with attendance at a tennis camp and swimming in an outdoor pool at the camp. Fecal contamination was detected in 

nonpotable well water delivered to outdoor faucets located at multiple locations around the tennis courts. Faucets were intended for irrigation, but no 

signs were posted to warn the public about nonpotable water. 
Vol. 57 / SS-9 Surveillance Summaries 47 

TABLE 7. Waterborne-disease outbreaks associated with drinking water (DW) and water not intended for drinking (WNID) that 

were not included in previous Surveillance Summaries (n = four), by state— United States, 1979–2002 

No. of cases 

Water Month/ Predominant (deaths)† Type of Water 

State type Year Class Etiologic agent illness* (n = 126) system§ Deficiency¶ source Setting 

Louisiana WNID May 2002 III Pseudomonas aeruginosa** Skin 27 Not applicable 12 Unknown Factory 

Minnesota DW Jun 1979 IV Detergent AGI 2 Unknown 11D Unknown Golf course 

Tennessee DW Oct 1988 III Unidentified AGI 89 Ncom 3 Creek Restaurant 

Tennessee DW Sep 1995 III Hepatitis A Hep 8 Ind 2 Well, spring Private 

residences 

* Skin: illness, condition, or symptom related to skin; AGI: acute gastrointestinal illness; and Hep: viral hepatitis.

† Deaths are indicated in parentheses if they occurred. 

§ Ncom: noncommunity. Community and noncommunity water systems are public water systems that have >15 service connections or serve an average 

of >25 residents for >60 days/year. A community water system serves year-round residents of a community, subdivision, or mobile home park. A 

noncommunity water system serves an institution, industry, camp, park, hotel, or business and can be nontransient or transient. Nontransient systems 

serve >25 of the same persons for >6 months of the year but not year-round (e.g., factories and schools), whereas transient systems provide water to 

places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, and parks). Individual water systems are small 

systems not owned or operated by a water utility that have <15 connections or serve <25 persons. 

¶ Deficiency classification for drinking water, water not intended for drinking (excluding recreational water), and water of unknown intent (see Table 2). 

** Source: Hewitt DJ, Weeks DA, Millner GC, Huss RG. Industrial Pseudomonas folliculitis. Am J Ind Med 2006;49:895–9. 

FIGURE 2. Number* of waterborne-disease outbreaks 

associated with drinking water — United States, 2005–2006 

No. of

oubreaks 

No. of

states 

>4 1

3 1

2 2

1 7

0 39

* n = 20; numbers are dependent on reporting and surveillance activities 

in individual states and do not necessarily indicate that more outbreaks 

occurred in a given state. 

nity water systems, two (40.0%) were associated with untreated 

ground water, two (40.0%) were associated with a treatment 

deficiency, and one (20.0%) was associated with both a treatment deficiency and a distribution system deficiency. Among 

the two outbreaks involving individual water systems, both 

were associated with contaminated, untreated ground water. 

The one outbreak involving a community water system was 

associated with both a treatment deficiency and a distribution 

system deficiency (Table 10). 

Water sources. Seven (87.5%) of the eight WBDOs with 

deficiencies 1–3 were associated with ground water sources 

involving wells, and one (12.5%) WBDO was associated with 

surface water derived from a river (Table 9). Among the seven 

outbreaks related to ground water sources, four (57.1%) were 

associated with treatment deficiencies, either inadequate or 

interrupted chlorination as the only treatment provided, and 

three (42.9%) were associated with consumption of untreated, 

contaminated ground water, (Tables 9, 11, and 13; Figure 6). 

The surface water outbreak occurred during a period of heavy 

rainfall in a noncommunity system that provided inadequate 

filtration and disinfection. 

Deficiencies 5A, 6–11: Contamination of Water 

at Points Not Under the Jurisdiction of a 

Water Utility or at the Point-of-Use 

Twelve WBDOs were given a deficiency classification of 5A 

or 6–11. Ten (83.3%) of these WBDOs were associated with 

Legionella spp., one (8.3%) was associated with Giardia, and 

one (8.3%) was associated with norovirus G1 (Tables 4 and 5). 

Water-quality data. Water-quality data indicating a problem with the drinking water were available for 10 (83.3%) of 

the 12 WBDOs with an NWU/POU deficiency. Legionella 

spp. were isolated from the implicated water sampled in nine 

(90.0%) of 10 legionellosis outbreaks. Water testing in the 

norovirus outbreak detected norovirus in the storage tank 

(Maryland, 2006). No water was tested in the giardiasis outbreak; the outbreak was confirmed by clinical testing results. 

Deficiency 5A: Legionella in drinking water. All 10 of the 

drinking water-associated legionellosis WBDOs occurred in 

residential buildings, hotels, or in institutional settings and 

were related to the multiplication of Legionella spp. in the 

building plumbing systems. The majority of cases of 

legionellosis were diagnosed by urinary antigen testing, which 

is specific for L. pneumophila serogroup 1 (35). 

Deficiencies 6–11. Two WBDOs were associated with deficiencies 6–11. In one outbreak (California, July 2005), per­
48 MMWR September 12, 2008 

sons ill with giardiasis had used a water 

dispenser at a gym. The water dispenser 

had been removed at the time of the 

public health investigation and could 

not be tested; however, point-of-use 

contamination of the dispenser spout 

seemed the most likely cause of the outbreak. The second outbreak with a 

POU deficiency (Maryland, 2006) also 

had SWTD deficiencies 3 and 4. 

Deficiency 99A–B: Unknown/ 

Insufficient Information 

Concerning Contamination 

of Tap Water 

The deficiency involved in one 

(5.0%) of the 20 WBDOs could not 

be identified because the cause of contamination was unknown. Persons at a 

church served by a community water 

system became ill with cryptosporidiosis (Ohio, 2005). No 

communitywide outbreak was detected and no waterquality violations were detected, suggesting that the contamination might have occurred outside the jurisdiction of the 

water utility. Investigators noted antiquated and piecemeal 

water plumbing and sewage lines. However, because it was 

unclear that this outbreak was caused by premise plumbing 

contamination, this WBDO is not included in the analysis of 

the SWTD or NWU/POU deficiencies. 

Waterborne Disease and Outbreaks 

Associated with Water Not Intended for 

Drinking and Water of Unknown Intent 

Eight WBDOs were associated with either WNID (n = six) 

or WUI (n = two) (Table 6). The eight WNID/WUI outbreaks 

caused illness among at least 96 persons and resulted in seven 

deaths. All deaths were associated with legionellosis. Five 

(62.5%) WNID/WUI outbreaks involved ARI, and three 

(37.5%) involved AGI. One (12.5%) of the eight WNID/WUI 

outbreaks was categorized as a strength of evidence Class I ranking, two (25.0%) were ranked as Class II, three (37.5%) were 

ranked as Class III, and two (25.0%) were ranked as Class IV. 

Etiologic Agents 

Five (62.5%) of the eight WNID/WUI outbreaks were 

attributed to L. pneumophila serogroup 1; these five outbreaks 

affected 73 persons and resulted in seven deaths. Two of the 

WNID/WUI outbreaks were attributed to Giardia intestinalis 

and one outbreak was attributed to E. coli O157:H7 (Table 6). 

FIGURE 3. Number of waterborne-disease outbreaks associated with drinking water 

(n = 814),* by year and etiologic agent — United States, 1971–2006 

60 

50 

40 

30

20 

10 

0 

1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 

Year 

Mixed agents † 

Legionella spp. 

§ 

Unidentified 

Chemical 

Viral 

Bacterial 

Parasitic 

* Single cases of disease related to drinking water (n = 16) have been removed from this figure; 

therefore, it is not comparable to figures in previous Surveillance Summaries. †Beginning in 2003, mixed agents of more than one etiologic agent type were included in the 

surveillance system. However, the first observation is a previously unreported outbreak in 2002.

§Beginning in 2001, Legionnaires’ disease was added to the surveillance system, and Legionella

species were classified separately in this figure. 

FIGURE 4. Number* of waterborne-disease outbreaks 

associated with drinking water, by etiologic agent and month 

— United States, 2005–2006 

10 

Legionella spp.
 

8
 Infectious (other than Legionella spp.) 

Unidentified † 

6 

4 

2 

0 

Month 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

* n = 20. 

†Unidentified etiology includes suspected etiologies not confirmed during 

the outbreak investigation. 

Deficiencies 5B, 5C, 12, and 99D 

Each of the eight WNID/WUI outbreaks had one known 

deficiency: five (62.5%) involved Legionella spp. in the water 

system (deficiencies 5B and 5C), two (25.0%) involved WNID 

unrelated to Legionella (deficiency 12), and one (12.5%) 

involved WUI (deficiency 99D). Four (80.0%) of the five 

legionellosis outbreaks involved WNID (deficiency 5B). In 

three of these outbreaks, the aerosolized water from cooling 

towers was tested and identified as the source of Legionella 
Vol. 57 / SS-9 Surveillance Summaries 49 

FIGURE 5. Percentage of waterborne-disease outbreaks (WBDOs) associated with 

drinking water, by illness and etiology — United States, 2005–2006 

All illness (n = 20)* AGI only (n = nine)* 

Mixed agents** 

11.1% 

Acute Bacteria¶ 

† AGI 22.2% 

45.0% respiratory 

50.0% 

Viruses 

22.2% 

Hep 

5.0% 

§

Unidentified 

22.2% 

Parasites 

22.2% 

* AGI: acute gastrointestinal illness; ARI: acute respiratory illness; Hep: viral hepatitis. 

† All acute respiratory illness was attributed to Legionella spp.
 § Norovirus suspected based upon incubation period, symptoms, and duration of illness.
 

¶ Including one outbreak that involved multiple bacterial agents. 

** One outbreak that involved bacterial and viral agents. 

spp. In the fourth outbreak, epidemiologic and environmental testing implicated a decorative fountain in a restaurant (36). 

One legionellosis outbreak (20.0%) involved WUI (deficiency 

5C). In this outbreak (Pennsylvania, July 2005), environmental 

water testing failed to determine the source of Legionella spp. 

Among the three (37.5%) outbreaks unrelated to Legionella, 

two involved G. intestinalis, and one was caused by E. coli 

O157:H7. In the first giardiasis outbreak (California, July 2005), household members became ill while using 

canal water that had been piped into 

their home for washing and bathing. In 

the second giardiasis outbreak (Colorado 2006), hikers became ill after 

drinking water from a stream. The outbreak investigation revealed a greater 

risk for becoming ill among those hikers who were less rigorous in their 

water-treatment practices (i.e., boiling, 

filtering, or use of chemicals). One outbreak at a sports camp involving 14 persons was caused by E. coli O157:H7 

(Tennessee 2005). Whereas the environmental investigation did not identify this 

organism in the water, nonpotable 

water contaminated with coliforms was leaking onto the pool 

deck and the tennis courts (Table 6). 

Previously Unreported Outbreaks 

Reports of four previously unreported WBDOs associated 

with drinking water and WNID that occurred during 1979– 

2002 were received for this surveillance period (Table 7). 

TABLE 8. Number of waterborne-disease outbreaks (WBDOs) associated with drinking water (n = eight),* by etiologic agent and 

type of water system — United States, 2005–2006 

Type of water system† 

Community Noncommunity Individual Total § Mixed system 

Etiologic agent WBDOs Cases WBDOs Cases WBDOs Cases WBDOs Cases WBDOs Cases 

Bacteria 

Campylobacter spp. 

Escherichia coli O157, C. jejuni, 

and Escherichia coli O145 

Viruses 

Hepatitis A 

Norovirus G1 

Mixed agents¶ 

Norovirus G1,C. jejuni, and Norovirus G2 

Unidentified 

Unidentified** 

Total 

Percentage 

1 

1 

0 

0 

0 

0 

0 

0 

0 

0 

1 

(12.5) 

32 

32 

0 

0 

0 

0 

0 

0 

0 

0 

32 

(6.2) 

1 

0 

1 

2 

0 

2 

1 

1 

1 

1 

5 

(62.5) 

60 

0 

60 

196 

0 

196 

139 

139 

59 

59 

454 

(87.6) 

0 

0 

0 

1 

1 

0 

0 

0 

1 

1 

2 

(25.0) 

0 

0 

0 

16 

16 

0 

0 

0 

16 

16 

32 

(6.2) 

0 

0 

0

0 

0 

0 

0 

0 

0 

0 

0 

(0.0) 

0 

0 

0

0 

0 

0 

0 

0 

0 

0 

0 

(0.0) 

2 

1 

1 

3 

1 

2 

1 

1 

2 

2 

8 

(100.0) 

92 

32

60

212 

16

196

139 

139

75 

75

518 

(100.0) 

* WBDOs with deficiencies 1–4 and 13 (i.e., surface water contamination, ground water contamination, water treatment deficiency, distribution system 

contamination, and untreated chemical contamination of source water) were used for analysis. 

† Community and noncommunity water systems are public water systems that have >15 service connections or serve an average of >25 residents for >60 

days/year. A community water system serves year-round residents of a community, subdivision, or mobile home park. A noncommunity water system 

serves an institution, industry, camp, park, hotel, or business and can be nontransient or transient. Nontransient systems serve >25 of the same persons 

for >6 months of the year but not year-round (e.g., factories and schools), whereas transient systems provide water to places in which persons do not 

remain for long periods of time (e.g., restaurants, highway rest stations, and parks). Individual water systems are small systems not owned or operated 

by a water utility that have <15 connections or serve <25 persons. 

§ Excludes commercially bottled water and water not intended for drinking, therefore, not comparable to Surveillance Summaries before 2003–2004. 

¶ Multiple etiologic agent types (bacteria, parasite, virus, and/or chemical/toxin) identified. 

** Norovirus suspected based on incubation period, symptoms, and duration of illness. 
50 MMWR September 12, 2008 

TABLE 9. Number of waterborne-disease outbreaks (WBDOs) associated with drinking water (n = eight),* by etiologic agent and 

water source — United States, 2005–2006 

Water source 

Ground water Surface water Unknown Mixed source Total 

Etiologic agent WBDOs Cases WBDOs Cases WBDOs Cases WBDOs Cases WBDOs Cases 

Bacteria 

Campylobacter spp. 

Escherichia coli O157, C. jejuni 

and Escherichia coli O145 

Viruses 

Hepatitis A 

Norovirus G1 

Mixed agent type† 

Norovirus G1,C. jejuni, and Norovirus G2 

Unidentified 

Unidentified§ 

Total 

Percentage 

1 

1 

0 

3 

1 

2 

1 

1 

2 

2 

7 

(87.5) 

32 

32 

0 

212 

16 

196 

139 

139 

75 

75 

458 

(88.4) 

1 

0 

1 

0 

0 

0 

0 

0 

0 

0 

1 

(12.5) 

60 

0 

60 

0 

0 

0 

0 

0 

0 

0 

60 

(11.6) 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

(0.0) 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

(0.0) 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

(0.0) 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

(0.0) 

2 

1 

1 

3 

1 

2 

1 

1 

2 

2 

8 

(100.0) 

92 

32

60

212 

16

196

139 

139

75 

75

518 

(100.0) 

* WBDOs with deficiencies 1–3 and 13 (i.e., surface water contamination, ground water contamination, water treatment deficiency, and untreated chemical 

contamination of source water) were used for analysis. 

†Multiple etiologic agent types (bacteria, parasite, virus, and/or chemical/toxin) identified. 

§Norovirus suspected based on incubation period, symptoms, and duration of illness. 

TABLE 10. Number and percentage of waterborne-disease outbreaks (WBDOs) associated with drinking water (n = eight),* by 

type of deficiency (n = 10)†

 and type of water system — United States, 2005–2006 

Type of water system§ 

Community Noncommunity Individual Total ¶ Mixed system 

Type of deficiency No. (%) No. (%) No. (%) No. (%) No. (%) 

1: Untreated surface water intended for drinking 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0

2: Untreated ground water intended for drinking 0 0.0 2 33.3 2 100.0 0 0.0 4 40.0 

3: Treatment deficiency 1 50.0 3 50.0 0 0.0 0 0.0 4 40.0 

4: Distribution system deficiency, including storage 1 50.0 1 16.7 0 0.0 0 0.0 2 20.0 

Total 2 100.0 6 100.0 2 100.0 0 0.0 10 100.0 

* WBDOs with deficiencies 1–4 and 13 (i.e., surface water contamination, ground water contamination, water treatment deficiency, distribution system 

contamination, and untreated chemical contamination of source water) were used for analysis. 

†Certain WBDOs have multiple deficiencies that are tabulated separately. This table reports 10 deficiencies from eight WBDOs. 

§Community and noncommunity water systems are public water systems that have >15 service connections or serve an average of >25 residents for 

>60 days/year. A community water system serves year-round residents of a community, subdivision, or mobile home park. A noncommunity water 

system serves an institution, industry, camp, park, hotel, or business and can be nontransient or transient. Nontransient systems serve >25 of the same 

persons for >6 months of the year but not year-round (e.g., factories and schools), whereas transient systems provide water to places in which persons 

do not remain for long periods (e.g., restaurants, highway rest stations, and parks). Individual water systems are small systems not owned or operated 

by a water utility that have <15 connections or serve <25 persons. 

¶Excludes commercially bottled water and water not intended for drinking, therefore, not comparable to Surveillance Summaries before 2003–2004. 

TABLE 11. Number and percentage of waterborne-disease outbreaks (WBDOs) associated with drinking water (n = eight),* by 

type of deficiency (n = eight) and source of water — United States, 2005–2006 

Water source 

Ground water Surface water Unknown Mixed source Total 

Type of deficiency No. (%) No. (%) No. (%) No. (%) No. (%) 

1: Untreated surface water intended for drinking 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0

2: Untreated ground water intended for drinking 4 57.1 0 0.0 0 0.0 0 0.0 4 50.0 

3: Treatment deficiency 3 42.9 1 100.0 0 0.0 0 0.0 4 50.0 

Total 7 100.0 1 100.0 0 0.0 0 0.0 8 100.0 

* WBDOs with deficiencies 1–3 and 13 (i.e., surface water contamination, ground water contamination, water treatment deficiency, and untreated 

chemical contamination of source water) were used for analysis. 
Vol. 57 / SS-9 Surveillance Summaries 51 

TABLE 12. Number and percentage of waterborne-disease outbreaks (WBDOs) associated with drinking water (n = eight),* by 

predominant illness and type of water system — United States, 2005–2006 

Type of water system§ 

Community Noncommunity Individual Total ¶ Mixed system

Predominant illness† WBDOs Cases (%) WBDOs Cases (%) WBDOs Cases (%) WBDOs Cases (%) WBDOs Cases (%) 

ARI 0 0 (0.0) 0 0 (0.0) 0 0 (0.0) 0 0 (0.0) 0 0 (0.0) 

AGI 1 32 (100.0) 5 454 (100.0) 1 16 (50.0) 0 0 (0.0) 7 502 (96.9) 

Hep 0 0 (0.0) 0 0 (0.0) 1 16 (50.0) 0 0 (0.0) 1 16 (3.1)

Total 1 32 (100.0) 5 454 (100.0) 2 32 (100.0) 0 0 (0.0) 8 518 (100.0) 

* WBDOs with deficiencies 1–4 and 13 (i.e., surface water contamination, ground water contamination, water-treatment deficiency, distribution system 

contamination, and untreated chemical contamination of source water) were used for analysis. 

†ARI: acute respiratory illness; AGI: acute gastrointestinal illness; and Hep: viral hepatitis. 

§Community and noncommunity water systems are public water systems that have >15 service connections or serve an average of >25 residents for 

>60 days/year. A community water system serves year-round residents of a community, subdivision, or mobile home park. A noncommunity water 

system serves an institution, industry, camp, park, hotel, or business and can be nontransient or transient. Nontransient systems serve >25 of the same 

persons for >6 months of the year but not year-round (e.g., factories and schools), whereas transient systems provide water to places in which persons 

do not remain for long periods of time (e.g., restaurants, highway rest stations, and parks). Individual water systems are small systems not owned or 

operated by a water utility that have <15 connections or serve <25 persons. 

¶Excludes commercially bottled water and water not intended for drinking, therefore, not comparable to Surveillance Summaries before 2003–2004. 

TABLE 13. Number and percentage of waterborne-disease outbreaks (WBDOs) associated with drinking water (n = eight),* by 

predominant illness and water source — United States, 2005–2006 

Water source 

Ground water Surface water Unknown Mixed source Total 

Predominant illness† WBDOs Cases (%) WBDOs Cases (%) WBDOs Cases (%) WBDOs Cases (%) WBDOs Cases (%) 

ARI 0 0 (0.0) 0 0 (0.0) 0 0 (0.0) 0 0 (0.0) 0 0 (0.0) 

AGI 6 442 (96.5) 1 60 (100.0) 0 0 (0.0) 0 0 (0.0) 7 502 (96.9) 

Hep 1 16 (3.5) 0 0 (0.0) 0 0 (0.0) 0 0 (0.0) 1 16 (3.1) 

Total 7 458 (100.0) 1 60 (100.0) 0 0 (0.0) 0 0 (0.0) 8 518 (100.0) 

* WBDOs with deficiencies 1–3 and 13 (i.e., surface water contamination, ground water contamination, water treatment deficiency, and untreated chemical 

contamination of source water) were used for analysis. 

†ARI: acute respiratory illness; AGI: acute gastrointestinal illness; and Hep: viral hepatitis. 

An outbreak of gastroenteritis occurred among two patrons 

at a golf course (Minnesota, 1979). Acute illness occurred 

within minutes of consuming water from a water cooler 

located next to the golf course. The water dispenser had 

become contaminated after a bucket with detergent residues 

was used to fill the water container. 

During September–November 1995, a hepatitis A outbreak 

involved eight persons in a community (Tennessee, 1995). 

All ill persons reported consuming untreated drinking water 

from ground water sources. Water testing revealed fecal contamination in multiple wells from this community. 

One outbreak of gastroenteritis (Tennessee, October 1988) 

involved an unidentified etiologic agent. The outbreak report 

implicated water and ice served at a restaurant as the cause of 

gastroenteritis in 89 persons. Filtered and chlorinated stream 

water was used for drinking water and ice. Three days before 

the onset of illnesses, the sewage system at an upstream campground overflowed, which presumably overwhelmed the 

restaurant’s water-treatment system. 

One outbreak of Pseudomonas folliculitis among 27 persons 

occurred in an industrial facility (Louisiana, 2002) and was 

linked with the use of recycled water in the manufacturing 

process (37). Although this closed water system was chemically treated, substantially high concentrations of P. aeruginosa 

were detected in multiple water samples at the facility. 

Surveillance Reports Not Classified 

as Waterborne Disease and Outbreaks 

Nine surveillance reports potentially implicating drinking 

water or WNID were submitted during 2005–2006 but had 

insufficient epidemiologic and water-quality data to warrant 

inclusion in this report as WBDOs. For three reports of 

legionellosis clusters, common-point sources of transmission 

were not implicated. Three additional outbreak reports 

described gastroenteritis within minutes of ingesting drinks 

at restaurants. Apparently, each of these drinking sources had 

been contaminated with a cleaning product. Because it was 

unclear whether the water was contaminated before it was 

mixed into drinks, these outbreaks were classified as foodborne 

outbreaks. In 2006, members of three families became ill with 

giardiasis. Subsequent investigations failed to determine 

whether private wells serving these families were contaminated. 

An AGI outbreak among rafting company employees was 
52 MMWR September 12, 2008 

caused by Campylobacter jejuni, and the drinking water system was suspected to be contaminated. However, despite a 

thorough investigation, other potential locations of exposure 

could not be ruled out. Finally, four persons became ill with 

gastroenteritis, and Aeromonas hydrophila was isolated from 

one person. Because no evidence of ground water contamination was detected and the role of Aeromonas in causing waterborne disease has not been definitively established, these cases 

were not included as an outbreak. 

Discussion 

Drinking water outbreaks reported to WBDOSS provide 

important data concerning the etiology and trends of waterborne disease. Analysis of these data can provide insight into 

the effectiveness of EPA regulations, public health oversight, 

treatment methods, and risk factors for nonpublic systems 

and water contaminated outside the jurisdiction of public systems. However, because of incomplete detection, investigation, and reporting of these outbreaks and because the level of 

surveillance and reporting activity varies in different localities, these data are limited in representing the actual occurrence of waterborne-disease outbreaks. In addition, WBDOSS 

only captures single, nonoutbreak cases of waterborne disease 

caused by a limited number of agents (e.g., Naegleria fowleri 

and chemicals demonstrated in water); single cases caused by 

other waterborne agents are not captured. These factors contribute to the WBDOSS underestimating the burden of 

endemic waterborne disease related to drinking water. 

Multiple factors contribute to the ability of state and local 

public health agencies to recognize, investigate, and report 

waterborne-disease outbreaks. These agencies must recognize 

and link cases of illness to a common water source, which 

requires appropriate laboratory, epidemiologic, and environmental capacity to conduct appropriate investigations. Outbreaks often are recognized through either case investigations 

of laboratory-confirmed notifiable diseases or complaints of 

illness from citizens. This process requires ongoing communication and collaboration between the laboratory, epidemiology and environmental sections of public health agencies. 

Outbreak reporting might increase as waterborne disease 

becomes better recognized, water system deficiencies are identified, and state surveillance activities and laboratory 

capabilities increase (38–40). Consequently, recommendations 

for improving WBDO investigations 

FIGURE 6. Percentage of waterborne-disease outbreaks (WBDOs) associated with 

drinking water, by etiologic agent, water system, and water source — United States, 

2005–2006 

§¶ Etiologic agent (n = 20) Water system (n = eight) 

Legionella spp.
 

50.0% ¶
 Unidentified Individual Noncommunity 

10.0% 25.0% 62.5% 

† Bacteria Community 10.0% 12.5% 

Mixed agents* Parasites 5.0% 

Viruses 10.0%
 

15.0%
 

** Water source (n = eight) 

Surface water 

12.5% 

Ground water 

87.5% 

include enhancing surveillance activities, increasing laboratory support for 

clinical specimen and water sample testing, and assessing sources of potential

bias (41–43). 

The identification of WBDO etiologic agents depends on multiple factors. Investigators must recognize the 

WBDO in a timely manner so that

appropriate clinical specimens and

environmental samples can be collected. 

Subsequently, the laboratories involved 

must have the ability to test for the 

organism, chemical, or toxin in the 

clinical and water specimens.

WBDOSS data suggest that these 

capabilities are improving, given the 

reduction in the proportion of reported 

WBDOs with an unidentified etiology. 

During 1971–1996, the etiologic agent 

was unknown in 51% (338/668) of 

outbreaks; however, during 1997– 

2006, the etiologic agent was unidenti­ * Each WBDO involves more than one etiologic agent. 

† Other than Legionella spp. § Deficiencies 1–4. See Table 10. 

¶ Does not include commercially bottled water, therefore, not comparable to summaries before 

2003–2004. 

** Deficiencies 1–3. See Table 11. 

fied in 24% (35/146) of outbreaks 

(Figure 3). Reasons for improved etiologic attribution might include

increased testing for viral agents in clini­
Vol. 57 / SS-9 Surveillance Summaries 53 

cal and water specimens and refinement in water sampling 

and testing methods. In previous years, stool specimens were 

tested routinely for enteric bacterial pathogens and parasites, 

but testing for viral agents was rarely conducted. Identification of water contamination (by coliform bacteria that might 

indicate fecal contamination) can provide important information to the epidemiologic investigation and should be 

attempted when the investigation is conducted in a timely 

matter. However, collection of water samples also depends on 

local and state statutory requirements and the availability of 

investigators who know how to collect the samples. Analyses 

of specific pathogens and indicators of water contamination 

depend upon the availability of certified or approved laboratories. Many laboratories are certified to conduct standard 

analyses for fecal indicators and chemicals, but few laboratories have capabilities for identifying waterborne pathogens, 

and these tests might be expensive. Collecting water samples 

for pathogen identification might require sampling large quantities of water or filtering large volumes of water through special membranes. Methods for concentrating large volumes of 

water for testing are being developed and disseminated to multiple sites in the United States as standard protocols (44). 

Reporting and surveillance bias might 

occur because certain local and state 

public health agencies have enhanced 

capacity to investigate outbreaks. In 

addition, determining whether an 

increase or decrease in reporting reflects 

either an actual change in the incidence 

of outbreaks or reflects a change in the 

sensitivity of surveillance practices is 

unknown. For example, in states that 

collaborate with CDC in the Environmental Health Specialist Network’s 

waterborne-disease project (EHS-Net 

Water), the funding of waterborne disease coordinators improved waterborne 

disease surveillance and interagency 

communication, leading to the reporting of previously unreported WBDOs 

(Table 7) (31). In addition, EHS-Net 

Water states are also beginning to 

report more new outbreaks than they 

have in previous surveillance periods. 

Increased reporting likely is attributable 

to better communication, detection, 

investigation, and reporting and not as
 

a result of more outbreaks occurring. 

Another key limitation of the data 

collected by WBDOSS is that, for the 

most part, the information pertains only to outbreaks of waterborne illness and not to endemic waterborne illness, including both acute and chronic health effects. The epidemiologic 

trends and water-quality concerns observed in outbreaks might 

not necessarily reflect or correspond with trends associated 

with endemic waterborne illness. In response to the Congressional SDWA Amendments of 1996, EPA and CDC completed and reviewed a series of epidemiologic studies and 

convened a national workshop in 2005 to assess the magnitude of endemic waterborne AGI associated with consumption of public drinking water. A joint report on the results of 

these studies is available at http://www.epa.gov/nheerl/articles/ 

2006/waterborne_disease.html. The report includes multiple 

documents that discuss various methods for estimating the 

annual number of endemic waterborne-AGI cases associated 

with public drinking water systems in the United States. Two 

different but overlapping estimates of the number of endemic 

AGI cases in the United States were derived: 1) 4.3–11.7 million cases (45) and 2) 16.4 million cases associated with public drinking water systems (confidence interval: 5.5–32.8) (46). 

These estimates, however, only describe a portion of the 

annual incidence of endemic waterborne-disease cases. To fully 

FIGURE 7. Percentage of waterborne-disease outbreaks (WBDOs) associated with 

drinking water, by deficiency* — United States, 2005–2006

All deficiencies (n = 23)* 

Unknown 

4.3% (1)† 

Source water, treatment No water utility 

facility, or distribution jurisdiction or at 

§ system (SWTD) point-of-use 

43.5% (10) (NWU/POU)¶ 

52.2% (12) 

SWTD NWU/POU Contamination 

Untreated at point-of-use 

16.7% 

40.0% 

ground water 

Legionella spp. 

Distribution in drinking 

system water system 

20.0% 83.3% 

Treatment deficiency 

40.0%

* A total of 20 WBDOs but 23 deficiencies.
 

†Deficiency 99A. See Table 14.

§Deficiencies 1–4. See Table 14. 

¶Deficiencies 5A, 6–11, 99B. See Table 14. 
54 MMWR September 12, 2008 

TABLE 14. Waterborne-disease outbreaks associated with drinking water (n = 20), by deficiencies (n = 23)* — United States, 

2005–2006 

Deficiency No. of deficiencies 

Contamination of water at/in the water source, treatment facility, or distribution system (SWTD)† 

1: Untreated surface water intended for drinking 

2: Untreated ground water intended for drinking 

3: Treatment deficiency (e.g. temporary interruption of disinfection, chronically inadequate disinfection, 

or inadequate, or no filtration) 

4: Distribution system deficiency, including storage (e.g. cross-connection, backflow, and contamination of 

water mains during construction or repair) 

13: Current treatment processes not expected to remove a chemical contaminant (e.g., pesticide contamination 

of groundwater treated with disinfection only) 

A: Surface water 

B: Ground water 

Contamination of water at points not under the jurisdiction of a water utility or at the point-of-use (NWU/POU)§ 

5: Legionella spp. in water system 

A: Water intended for drinking 

6: Plumbing system deficiency after the water meter or property line (e.g. cross-connection, backflow, 

and corrosion products) 

7: Deficiency in building/home-specific water treatment after the water meter or property line 

8: Deficiency or contamination of equipment using or distributing water (e.g. drink-mix machines) 

9: Contamination during commercial bottling 

10: Contamination during shipping, hauling, or storage 

A: Water intended for drinking – Tap water 

B: Water intended for drinking – Commercially bottled water 

11: Contamination at point-of-use 

A: Tap 

B: Hose 

C: Commercially bottled water 

D: Container, bottle, or pitcher 

E: Unknown 

Unknown/Insufficient Information 

99: Unknown/Insufficient information 

A: Water intended for drinking – Tap water 

B: Water intended for drinking – Commercially bottled water 

Total no. of deficiencies* 

10 

0 

4 

4 

2 

0 

0 

12 

10 

0 

0 

0 

0 

0 

0 

0 

1 

0 

1 

0 

1 

1 

0 

23 

* More than one deficiency might have been identified during the investigation of a single waterborne-disease case or outbreak or case. 

†Contamination of water and deficiencies occurring in the drinking water system at/in the water source, treatment facility, or distribution system of pipes 

and storage facilities. For a community water system, the distribution system refers to the pipes and storage infrastructure under the jurisdiction of the 

water utility before the water meter or property line (if the system is not metered). For noncommunity and nonpublic water systems, the distribution 

system refers to the pipes and storage infrastructure before entry into a building or house (e.g., in a service line leading to a house or building). 

§Contamination of drinking water and deficiencies occurring in plumbing and pipes that are not part of the distribution system or at other points outside 

the jurisdiction of a water utility as previously defined. For community systems, this means that after the water meter or property line (if the system is not 

metered) and for noncommunity and nonpublic systems, this means within the building or house (e.g., in the plumbing inside a house or building) during 

shipping or hauling, during storage other than in the distribution system, and at the point-of-use). 

describe the overall incidence of waterborne disease, estimates WBDOs Associated with Drinking Water 

also need to include the number of cases of waterborne disEtiologic Agents ease other than AGI and the number of cases associated with 

nonpublic drinking water systems, commercially bottled Since its addition to WBDOSS in 2001, Legionella has been 

water, recreational water, WNID, and WUI. If these other the single most commonly reported pathogen associated with 

types and sources of waterborne disease were considered, the drinking water outbreaks. During 2005–2006, a total of 10 

estimated number of cases of endemic waterborne disease (50.0%) of the 20 reported drinking water-associated WBDOs 

would be higher than the existing estimates of 4–33 million involved Legionella spp, which is the first time that the numannual cases (45,46). ber of reported WBDOs associated with ARI has surpassed 

those associated with AGI in any surveillance period. These 

WBDOs all occurred as a result of Legionella colonization of 

plumbing and pipes that are not under the jurisdiction of a 

water utility and are not specifically subject to EPA regulations. As the predominant drinking water-related pathogen 
Vol. 57 / SS-9 Surveillance Summaries 55 

in WBDOSS, increased attention must be focused on 

Legionella to understand its biology, ecology, and inactivation 

in parts of the water system not addressed by federal regulation so that appropriate public health action to prevent further WBDOs can be taken. 

During the 2005–2006 surveillance period, two drinking 

water-associated WBDOs involved only bacteria (excluding 

Legionella spp.), compared with five during the 2003–2004 

and three during the 2001–2002 surveillance periods. The 

ongoing occurrence of bacterial WBDOs, despite available 

and efficacious treatment practices, underscores the continuing need for protection and treatment of drinking water (47). 

In addition, one mixed-agent type outbreak occurred during 

the 2005–2006 surveillance period, which included bacteria 

(C. jejuni) and viruses (norovirus G1 and G2). The occurrence 

of mixed-agent type and multiple agent outbreaks emphasizes 

the importance of considering more than one etiologic agent in 

outbreak investigations, collecting appropriate specimens for 

each agent type, and requesting appropriate diagnostic testing 

for each agent type. In addition, this outbreak was associated 

with sewage contamination of a well, underscoring the importance of proper waste management and proper drinking water 

system and waste water system designs. 

Three WBDOs involving only viruses were reported for the 

2005–2006 surveillance period. Two involved norovirus G1, 

and one involved hepatitis A. Based on incubation period, 

symptoms, and duration of illness, norovirus was also suspected in the two WBDOs where the etiologic agent was unidentified. All of these WBDOs involved contaminated ground 

water that was either untreated or improperly treated (inadequate or interrupted chlorination as the only treatment provided). EPA’s GWR is designed to address vulnerable public 

ground water systems. However, two of these viral outbreaks 

occurred in individual nonpublic water systems, and the GWR 

does not apply to these water systems. 

Parasites were identified in two WBDOs during the 2005– 

2006 surveillance period. The giardiasis outbreak (California, 

August 2005) was associated with point-of-use contamination. The reason for contamination could not be determined 

for the Cryptosporidium outbreak; however, investigators noted 

antiquated and piecemeal water plumbing and sewage lines, 

suggesting that contamination might have entered through 

water plumbing (Ohio, September 2006). No parasitic outbreaks were associated with contaminated surface water in this 

surveillance period. Both public surface water systems and 

public ground water systems under the influence of surface 

water are regulated under SWTR to protect the public against 

exposure to Giardia and Cryptosporidium, among other pathogens. The last parasitic disease outbreak associated with surface water and reported to CDC occurred in 2002 in Palau in 

an untreated noncommunity system supplied by a river. The 

dramatic decrease in the number of outbreaks caused by parasites (Figure 3) might be attributable to enhanced EPA regulation of surface water sources. 

The etiologic agents of two WBDOs could not be identified, although norovirus was suspected. These two outbreaks 

represent 10.0% of the 20 drinking water-associated WBDOs 

reported during 2005–2006 (Figure 6). These two WBDOs 

represent the lowest number and percentage of outbreaks 

caused by an unknown etiology in any surveillance period 

since the beginning of the surveillance system in 1971. This 

decrease might reflect improved diagnostic capabilities of laboratories and better outbreak investigations, resulting in more 

rapid and more appropriate specimen collection. 

Deficiencies 1–4 and 13: Contamination 

of Water at/in the Water Source, Treatment 

Facility, or Distribution System 

Typically, EPA regulates the community drinking water supplies from the source water up to the water meter (or up to 

the property line if the distribution system is not metered). 

This segment of the drinking water supply system is associated with deficiencies 1–4 and 13 (Table 2): 1) consumption 

of untreated surface water intended for drinking, 2) consumption of untreated ground water intended for drinking, 3) treatment deficiencies, 4) distribution system deficiencies, and 13) 

chemical contamination of source water not removed by 

existing treatment methods. Noncommunity and individual 

nonpublic systems also might have distribution system deficiencies (i.e., deficiency 4) if problems occur in pipes or storage infrastructure before entry into a building or house. During 

the 2005–2006 surveillance period, 40.0% of drinking 

water-related outbreaks (n = 8) and 43.5% of deficiencies 

(n = 10) involved deficiencies 1–4. A single WBDO can be 

associated with more than one deficiency. Deficiency 13 was 

not implicated in any outbreak during the 2005–2006 surveillance period. 

Source water. Discussions regarding source water type only 

include those WBDOs with deficiencies 1–3 because distribution system deficiencies (deficiency 4) are not necessarily 

dependent upon the source water type. Also excluded from 

the discussion involving source water types are drinking waterassociated WBDOs with unknown or insufficient information (deficiencies 99A) and outbreaks associated with 

contamination at points not under the jurisdiction of a water 

utility or at the point-of -use (deficiencies 5A, 6–11, and 99B). 

Surface water. Only one (12.5%) of the eight outbreaks 

with deficiencies 1–3 was associated with consumption of 

inadequately-treated surface water. In this outbreak (Oregon, 

2005), chronically-inadequate chlorination and inadequate 
56 MMWR September 12, 2008 

filtration of the river water supplying the camp were cited as 

the underlying reasons for illness among camp attendees. Since 

the early 1990s, the percentage of reported WBDOs associated with inadequately treated surface water has been declining. This decrease is likely attributable to EPA regulations 

mandating treatment of surface water used by public water 

systems. However, this outbreak underscores that regulations 

alone do not prevent outbreaks and that attention to proper 

water system operation and maintenance is still required. 

Ground water. Seven (87.5%) of the eight outbreaks with 

deficiencies 1–3 were associated with consumption of contaminated ground water, either from wells or springs. Among 

these seven outbreaks, four (57.1%) involved consumption 

of untreated ground water (deficiency 2), and three (42.9%) 

involved treatment deficiencies associated with contaminated 

ground water (deficiency 3). These seven ground waterassociated outbreaks indicate that ground water contamination is a continuing problem. Wells and springs must be 

protected from contamination, even if disinfection is provided, 

because ground water can become contaminated with pathogens that are not easily disinfected, and source water conditions might overwhelm the disinfection process (e.g., highly 

turbid water as a result of excessive rain fall). 

Five of the seven outbreaks associated with contaminated 

ground water during the 2005–2006 surveillance period 

occurred in noncommunity or community water systems that 

will be subject to EPA’s new GWR. Beginning in 2009, the 

GWR will apply to all public systems that use ground water 

as a source of drinking water. Although this new rule has not 

yet been fully implemented, it will establish a risk-based 

approach to target ground water systems that are vulnerable 

to fecal contamination. The risk-targeting approach includes 

four major components: 1) sanitary surveys, 2) source water 

monitoring to test for the presence of indicators of fecal contamination in the ground water source, 3) corrective action, 

and 4) compliance-monitoring to ensure that the treatment 

technology installed to treat drinking water reliably achieves 

at least 99.99% (4-log) inactivation or removal of viruses. 

Operators of ground water systems that are identified as 

being at risk for fecal contamination must take corrective 

action to reduce the potential for illness from exposure to 

microbial pathogens. 

Because EPA regulations do not apply to individual, 

nonpublic water systems, WBDOs such as the two involving 

individual ground water systems reported during 2005–2006 

will not be subject to the GWR, which could potentially prevent such outbreaks. The protections offered by the GWR 

will not extend to individual ground water systems unless they 

are regulated by state or local authorities. Approximately 17 

million persons in the United States rely on private household wells for drinking water each year, and more than 90,000 

new wells are drilled annually throughout the United States 

(48). To safeguard the quality of well water, homeowners 

should seek information on needed protective measures and 

implement recommended operation and maintenance guidelines for private well usage. Homeowners may also choose to 

protect their own health by purchasing appropriately designed 

point-of-use water-treatment devices and by following instructions for their proper operation and maintenance. Although 

EPA does not regulate individual water systems, EPA recommendations for protecting private wells are available at 

http://www.epa.gov/safewater/pwells1.html. Additional efforts 

should be taken by public health officials to educate well owners, users, drillers, and local and state drinking water personnel to encourage practices that best ensure safe drinking water 

for private well-users. 

Water treatment. During 2005–2006, five drinking waterrelated WBDOs associated with water-treatment deficiencies 

were reported; all were associated with inadequate chlorination. One WBDO was associated with a malfunctioning chlorine feeder (Indiana, 2006). Two outbreaks occurred because 

existing water treatment was overwhelmed. Heavy rain might 

have overwhelmed a camp surface water-treatment system in 

one outbreak (Oregon, 2005), and remnants of Hurricane 

Katrina might have created surface water runoff into a spring 

supplying drinking water to a restaurant in the other outbreak (Ohio, 2005). In addition, this small restaurant served 

a tour group that was substantially larger than was typically 

served, and the chlorination system could not keep up with 

the demand for water. The remaining two WBDOs had inadequate chlorination, but the causes were not specified in the 

reports. All five outbreaks indicate the need for proper equipment maintenance, adequate capacity of treatment systems to 

provide potable water during occasional periods of high 

demand, and education of small water system operators and 

owners concerning the operation, routine monitoring, and 

capability of treatment systems under various conditions. 

Although treatment deficiencies (deficiency 3) made up the 

greatest proportion (50.0%) of SWTD deficiencies during 

the 2005–2006 surveillance period, the majority of (80.0%) 

of these treatment deficiencies were associated with failures to 

adequately treat contaminated ground water. When these 

deficiencies are considered with deficiency 2, contaminated 

ground water becomes the single largest contributing factor 

to SWTD-related outbreaks, underscoring the need for the 

GWR previously described. 

Distribution system. Distribution system deficiencies make 

up the smallest proportion of the SWTD deficiencies during 

this surveillance period. During 2005–2006, two drinking 

water-related WBDOs involving distribution system deficien­
Vol. 57 / SS-9 Surveillance Summaries 57 

cies occurred. Before one outbreak (Indiana, 2006), a new 

water main was installed without a valid permit. The water 

main was pressure tested and was left under pressure with 

nonpotable water, resulting in a cross-contamination hazard. 

In the second outbreak, backflow prevention devices were 

absent on water distribution lines to toilet facilities in a camp 

(Maryland, 2006). Drinking water quality within the distribution systems of public water supplies is regulated under EPA’s 

TCR, which is currently undergoing revisions to better protect public health. 

Water systems. Discussions regarding water system types 

(i.e., community, noncommunity, and individual) include 

drinking water-associated WBDOs with deficiencies 1–4 and 

13. Deficiencies in the distribution system are included in 

these discussions because distribution system problems might 

be dependent on the type of water system involved. Among 

the eight drinking water-associated WBDOs with a deficiency 

of 1–4, a total of five (62.5%) were associated with noncommunity water systems, two (25.0%) with individual water systems, and one (12.5%) with a community water system. The 

proportion (12.5%) of drinking water-related WBDOs associated with community water systems represents the lowest 

proportion of outbreaks that occurred during the last four 

surveillance periods (i.e., 1999–2000, 2001–2002, 2003– 

2004, and 2005–2006). This decrease might reflect the success of federal drinking water regulations protecting water 

quality in public supplies. 

Environmental investigation. To better understand the 

antecedent events resulting in drinking water-associated 

WBDOs, particularly deficiencies 1–4, a new outbreak investigation tool is being developed by EHS-Net, a collaborative 

forum of environmental health specialists. These environmental health specialists collaborate with epidemiologists and 

laboratorians to identify, investigate, and prevent environmental factors contributing to foodborne and waterborne illness 

and disease outbreaks. In 2000, EHS-Net Food was established with funds from CDC’s National Center for Environmental Health, Environmental Health Services Branch, and 

the FDA and has nine participating state sites that focus on 

the prevention of foodborne disease. In 2005, EHS-Net 

Water was piloted with CDC and EPA funds, which support 

one staff member in each of five states (California, Georgia, 

Minnesota, New York, and Tennessee) to focus specifically on 

waterborne-disease investigations. The environmental outbreak 

investigation tool developed by EHS-Net Water assists with 

outbreak investigations both by capturing environmental data 

that are not collected routinely (e.g., assessment of water system operations) and by clarifying the environmental events and 

situations (e.g., recent precipitation events) that contributed to 

WBDOs in small ground water systems. This information will 

assist public health officials and water system operators and 

owners in addressing the potential sources of contamination 

that resulted in an outbreak of waterborne disease. 

Deficiencies 5A and 6–11: Contamination 

of Water at Points Not Under the Jurisdiction 

of a Water Utility or at the Point-of-Use 

A distinction can be made between deficiencies that occur 

at points NWU/POU and SWTD. During the 2005–2006 

surveillance period, more WBDOs were associated with 

NWU/POU (12 [52.2%]) than with SWTD (10 [43.5%]) 

(Figure 7). Similar proportions were noted in the 2003–2004 

surveillance period, which was the first time the distinction 

was made between NWU/POU and SWTD deficiencies. 

Deficiency 5A. Legionella in water intended for drinking. 

Legionellosis includes two clinically distinct syndromes: 

Legionnaires’ Disease (LD), characterized by severe pneumonia, and Pontiac Fever (PF), a febrile, cough illness that does 

not progress to pneumonia. Legionellosis outbreaks accounted 

for 50% of all drinking water-associated WBDOs reported 

during 2005–2006 and 83.3% of all NWU/POU deficiencies, indicating that Legionella is a serious public health threat. 

When outbreaks of legionellosis occur in the setting of contaminated drinking water, they typically manifest as cases of 

LD rather than PF. Approximately 8,000–18,000 cases of LD 

occur each year in the United States (49). Regardless of the 

syndrome, the source of legionellosis outbreaks typically share 

common features (e.g., warm stagnant water, inadequate biocide concentrations, and aerosolization, which provides the 

mechanism for inhalation). 

The outbreaks of legionellosis highlight the challenges 

related to its detection and prevention. LD is underdiagnosed 

because the majority of patients with community-acquired 

pneumonia are treated empirically with broad-spectrum antibiotics (50). However, because Legionella spp. are not transmitted from person-to-person and are always acquired from 

an environmental source, even a single case of LD implies the 

presence of a contaminated aquatic source to which others 

can be exposed. Certain host factors (e.g., underlying lung 

disease and immunodeficiencies) influence the development 

and severity of legionellosis. Typically, the attack rate during 

documented LD outbreaks is quite low (i.e., <5%). Not 

everyone who is exposed in a Legionella-contaminated building is susceptible to symptomatic illness. Identification of two 

or more cases of LD in association with a potential source is 

adequate justification for an investigation. All of the 

legionellosis outbreaks described in this report involved ten 

or fewer cases. Nonetheless, in all instances except for one, 

the epidemiologic and laboratory data were compelling enough 

to implicate point sources that were subsequently remediated. 
58 MMWR September 12, 2008 

During 2005–2006, a total of eight (80%) of 10 legionellosis 

outbreaks associated with drinking water occurred in healthcare settings, demonstrating the propensity for Legionella spp. 

to colonize potable water systems and underscoring the 

importance of maintaining a high index of suspicion for 

legionellosis in health-care settings. Seven outbreaks occurred 

in acute-care hospitals and one in a long-term–care facility. 

Legionella spp. colonize the biofilm layer frequently found 

inside the large, complex plumbing systems of hospitals (51). 

This biofilm protects Legionella from biocides and allows the 

bacteria to amplify to levels sufficient to be transmitted and/ 

or cause disease. Patients in hospitals or long-term–care facilities typically are older and have underlying illness factors that 

increase the risk for disease (e.g., chronic lung disease, diabetes, and immunocompromising conditions). 

An outbreak of legionellosis in a health-care setting should 

prompt both an epidemiologic and environmental investigation. Additional cases might point to water exposures that 

contributed to the outbreak. Environmental sampling of the 

potable water system and other aerosolized water exposures 

(e.g., cooling towers) can confirm the source of the outbreak 

and lead to targeted interventions that prevent additional cases. 

Superheating and superchlorination are the traditional methods for remediation; however, Legionella might regrow in the 

distribution system (52). Other remediation options are 

under investigation. Monochloramine might be an effective 

biocide for Legionella control; hospitals supplied with drinking water containing monochloramine were less likely to have 

a reported outbreak of LD than those that used water with free 

chlorine as a residual disinfectant (53). Each health-care facility 

should develop a plan for legionellosis prevention to address 

predisposing conditions for Legionella growth in the potable 

water supply. Guidelines for reducing the risk for legionellosis 

associated with building water systems are available (52). 

Deficiencies 6–11. Deficiencies involving drinking water 

that occur at points not under the jurisdiction of a water utility or at the point-of-use have been presented (Table 2). During the 2005–2006 surveillance period, only two reported 

non-Legionella WBDOs involving deficiencies in this category 

were reported. Both WBDOs involved point-of-use contamination. One outbreak of giardiasis was associated with contamination of a 5-gallon drinking water ceramic crock 

dispenser at a gym (California, August 2005). Epidemiologic 

evidence linked all the cases to the dispenser, although the 

mechanism of contamination of the dispenser could not be 

determined. The dispenser had a hand-manipulated spigot 

and the water was typically replenished once a day, although 

the dispenser was not regularly cleaned during the suspected 

period of exposure. Investigators thought that either the employee who replenished the water (she was asymptomatic but 

her boyfriend was a laboratory-confirmed case) or an ill gym 

patron who used the spigot might have contaminated the water. 

An outbreak of norovirus G1 at a camp (Maryland 2006) 

involved water-treatment and distribution-system deficiencies 

in addition to contamination at the point-of-use. Garden hoses 

stored improperly on the ground were used to fill large water 

containers from which campers filled their cups and water 

bottles. These point-of-use contamination events illustrate the 

vulnerability of shared water containers and the importance 

of practicing good hygiene. 

Waterborne Disease and Outbreaks 

Associated with Water Not Intended 

for Drinking and Water of Unknown 

Intent 

During the 2005–2006 surveillance period, eight WBDOs 

occurred that were associated with WNID or WUI. Five of 

these outbreaks were associated with Legionella spp. Three of 

these outbreaks were in health-care settings and attributed to 

cooling towers. Although the building potable water system 

is more frequently implicated in health-care–associated outbreaks, community sources should also be considered. Aerosols containing Legionella can travel great distances; an 

investigation of an outbreak among residents of a long-term 

care facility implicated a cooling tower that was 0.4 km from 

the facility (54). 

Legionellosis clusters might signal a wider community outbreak and should prompt an investigation. In addition, 

legionellosis outbreaks also can occur in the general population outside the health-care setting, as demonstrated by a community outbreak in South Dakota in 2005. The epidemiologic 

investigation revealed that a restaurant was the common 

exposure among cases. Targeted environmental testing ultimately confirmed the source as the decorative fountain inside 

the restaurant (36). The source of contaminated water could 

not be identified for the fifth legionellosis outbreak. 

The other three non-Legionella WNID/WUI outbreaks were 

associated with bacterial and parasitic diseases. An outbreak 

caused by E. coli O157:H7 occurred at a sports camp (Tennessee 2005). The primary water exposure associated with illness could not be identified. Illness was associated with 

swimming in one of the outdoor pools, dining at pool picnic 

tables, and attending a tennis camp. Unlabeled irrigation faucets drawing water from a nonpotable well were located at 

multiple points around the tennis courts. Sampling of this 

water system detected fecal contamination. The remaining two 

WBDOs involved cases of giardiasis that developed after 

exposure to WNID. One outbreak involved a family who had 

canal water piped into their home to use for bathing, dish 
Vol. 57 / SS-9 Surveillance Summaries 59 

washing, house cleaning, and laundry (California, July 2005). 

The second outbreak involved a school trip to a state forest 

(Colorado 2006). Six of 26 campers became ill. The epidemiologic data indicated that inadequate treatment of river 

water before consumption was a risk factor. Adding a sports 

drink powder to river water while concurrently adding iodine 

for disinfection was a statistically-significant risk factor for 

becoming ill. The relative risk for boiling water <3 minutes 

could not be defined because none of the persons who boiled 

water longer became ill. Both of these giardiasis outbreaks 

illustrate the risks associated with consuming untreated 

surface water, even water that might appear pristine. 

Backcountry travel (i.e., travel in wilderness environments) 

in the United States is an increasingly popular activity. In 2004, 

approximately 12% of Americans aged >16 years (approximately 26 million persons) went backpacking for one or more 

nights in backcountry areas during the previous 12 months 

(55). Limited information is available concerning the risk factors for illness in the backcountry and about the health outcomes of visitors who use parks in backcountry areas. Several 

studies indicate that as many as 3.8%–56% of long-distance 

hikers and backpackers experience gastrointestinal illness during their time in the backcountry (56–61). Given the increasing popularity of backcountry use, this burden of illness could 

have significant medical and economic implications. Although 

the advice to universally filter and disinfect backcountry drinking water to prevent disease has been debated (62), the health 

consequences of ignoring that standard water treatment 

advice have been documented in WBDOSS, although they 

have not been well-defined through research studies. 

Previously Unreported Outbreaks 

This report discusses information concerning four previously unreported WBDOs. Two of these outbreaks occurred 

in Tennessee, one in Minnesota, and one in Louisiana. The 

Tennessee and Minnesota state health departments are partners in EHS-Net Water. Initial surveys by three of the five 

participating EHS-Net Water states have revealed at least 75 

outbreaks or health events previously unreported to CDC, 

including the three drinking water outbreaks reported in this 

Surveillance summary, nine drinking water outbreaks from New 

York State included in the previous Surveillance Summary (5), 

and 63 recreational water-related outbreaks or health events 

reported in the recreational water Surveillance Summary (30). 

In addition to reporting historical outbreaks, these states are 

working to improve the sensitivity of their current waterbornedisease outbreak detection. Additional EHS-Net Water projects 

are underway to improve the practice of environmental health 

service programs; translate the findings into improved prevention efforts; offer training opportunities to current and 

future environmental health specialists; and strengthen the 

collaboration among epidemiology, laboratory, and environmental health programs. The EHS-Net Water activities 

indicate that increased effort and resources, specifically 

directed at waterborne-disease reporting, could result in the 

identification of previously unreported historical outbreaks. 

As EHS-Net Water refines the process for identifying and 

investigating current waterborne-disease incidents, these 

efforts might result in enhanced reporting of waterborne 

outbreaks from these and other states. 

Conclusion 

Data collected as part of the national WBDOSS are used to 

describe the epidemiology of waterborne-disease outbreaks in 

the United States. Trends regarding water systems and deficiencies implicated in these WBDOs are used to assess whether 

regulations for water treatment and water-quality monitoring 

are adequate to protect public health. Trends regarding the 

etiologic agents responsible for these outbreaks are used to 

assess the need for different interventions and changes in policies and resource allocations. 

Two primary trends can be observed from the 2005–2006 

surveillance period data. Since it was first included in 

WBDOSS in 2001, Legionella has become the single most 

common cause of reported outbreaks in WBDOSS. This does 

not mean that Legionella is a more important cause of waterborne disease than other agents (e.g. norovirus) nor does it 

mean than legionellosis outbreaks are increasing because they 

have only been included in the WBDOSS since 2001. Therefore, there is a limited basis for historical comparison. However, outbreaks associated with other agents are not being 

reported as frequently as outbreaks caused by Legionella. 

Whether this is a result of barriers to laboratory confirmation 

of non-Legionella pathogens in clinical specimens and environmental samples, lack of detection of non-Legionella pathogens 

as a result of different incubation periods or milder illness, use 

of adequate water-treatment technologies for non-Legionella 

pathogens, or other factors that might be responsible for fewer 

outbreaks associated with non-Legionella is not clear. 

The second major trend observed in the 2005–2006 surveillance period is the high proportion of WBDOs associated 

with contaminated ground water, whether consumed untreated 

or with inadequate treatment. Until the GWR was finalized 

in 2006, federal drinking water regulations have concentrated 

on protecting consumers from contaminated surface water. 

These rules probably have contributed to the decrease in the 

number and proportion of reported WBDOs associated with 

contaminated surface water that have been observed during 
60 MMWR September 12, 2008 

the previous twenty years. Similar protections against the consumption of contaminated ground water were absent until 

the development of the GWR, which was finalized in 2006. 

This rule, which is expected to be enacted in 2009, might 

result in a similar decline in the number of ground water– 

associated WBDOs. 

Surveillance for waterborne agents and WBDOs occurs primarily at the local and state levels (including territories and 

FAS). Public health authorities at these levels are responsible 

for detecting and recognizing drinking water-associated 

WBDOs and implementing appropriate prevention and control measures (Box). Improved communication among local 

and state public health departments, regulatory agencies, and 

water utilities will aid in the detection and control of WBDOs. 

Routine reporting or sharing of water-quality data within the 

health and environmental health departments is recommended. 

Other means of improving surveillance at the local, state, and 

federal levels include additional review and follow up of information gathered through other mechanisms (e.g., issuances of 

boil-water advisories or reports of illness associated with agents 

thought to be waterborne). 

A number of efforts have been initiated at the local, state, 

and national levels to improve the detetection, investigation, 

and reporting of WBDOs. CSTE passed a position statement 

at the 2006 annual meeting making WBDOs, as a unit of 

reporting, nationally notifiable and reportable to CDC starting in 2007. Adoption of this CSTE recommendation at the 

state level through state-specific legislative action might 

improve reporting of WBDOs at the state and local levels. 

In addition, to improve timeliness and completeness of 

reporting, CDC and EPA are collaborating with public health 

jurisdictions to implement electronic reporting of WBDOs 

BOX. Organizations that provide assistance in investigations of waterborne disease and outbreaks (WBDOs) 

State and territorial health departments can request Telephone: 404-639-2215 

epidemiologic assistance and laboratory testing from Internet: http://www.cdc.gov/legionella 

CDC to investigate WBDOs. CDC and the U.S. Envi­ • Testing for Parasites ronmental Protection Agency (EPA) can be consulted Division of Parasitic Diseases regarding engineering and environmental aspects of National Center for Zoonotic, Vector-Borne, and drinking water treatment during and after outbreaks and Enteric Diseases 

collection of large-volume water samples to identify Coordinating Center for Infectious Diseases, CDC pathogens that require special protocols for their recov- Telephone: 770-488-7775 ery. EPA and the U.S. Geological Survey can be consulted for assistance with hydrogeologic investigations • Testing for Viruses 

of outbreaks where untreated ground water is suspected. Division of Viral Diseases 

National Center for Immunization and Respiratory • Environmental Protection Agency Safe Drinking Diseases 

Water Hotline Coordinating Center for Infectious Diseases, CDC Telephone: 800-426-4791 Telephone: 404-639-3607 E-mail: hotline-sdwa@epa.gov 

Internet: http://www.epa.gov/safewater • State Reporting of Waterborne Disease and

 Outbreaks 

• Testing for Bacterial Enteric Organisms Division of Parasitic Diseases 

Division of Foodborne, Bacterial, and Mycotic National Center for Zoonotic, Vector-Borne, and 

Diseases Enteric Diseases 

National Center for Zoonotic, Vector-Borne, and Coordinating Center for Infectious Diseases, CDC Enteric Diseases Telephone: 770-488-7775 Coordinating Center for Infectious Diseases, CDC Fax: 770-488-7761 

Telephone: 404-639-1798 Note: All WBDOs at the local level should be 

reported to the state health department. • Request for Information on Testing for Legionella

Division of Bacterial Diseases • CDC Reporting Form CDC 52.12 (rev.01/2003) National Center for Immunization and Respiratory Internet: http://www.cdc.gov/healthyswimming/ Diseases downloads/cdc_5212_waterborne.pdf Coordinating Center for Infectious Diseases, CDC 
Vol. 57 / SS-9 Surveillance Summaries 61 

through the National Outbreak Reporting System (NORS). 

NORS is a more systematic data-collection tool and will provide public health agencies and waterborne-disease researchers with the evidence base they need to identify the causes of 

WBDOs and understand the environmental factors contributing to these outbreaks. 

EHS-Net Water, a collaborative project between EPA, CDC, 

and five state health departments, is an effort to improve 

WBDO identification, investigation, response, and reporting. 

EHS-Net Water sites initially focused on understanding their 

state-specific surveillance systems, which resulted in the identification and reporting of numerous previously unreported 

historical outbreaks to WBDOSS. Subsequent efforts are 

focusing on improving the environmental investigation of 

drinking water outbreaks, particularly in small groundwater 

systems. 

In May 2007, EPA and CDC convened a workshop to 

address improving the recognition, investigation, and reporting of waterborne-disease outbreaks. Participants included 

epidemiologists, environmental engineers, scientists, environmental health specialists, other public health professionals, and 

water-industry professionals from 44 states, the District of 

Columbia, and Puerto Rico. Workshop recommendations 

included 1) improving the communication and coordination 

between agencies investigating waterborne-disease outbreaks; 

2) conducting training for outbreak investigators, laboratory 

analysts, and water system operators; 3) focusing efforts on 

outbreak prevention; 4) enhancing surveillance; 5) strengthening outbreak investigations; and 6) improving outbreak 

reporting. 

Efforts to enhance awareness, training, resources, and communication will improve the quality of the data in WBDOSS. 

These efforts should make public health activities related to 

waterborne disease more efficient and reduce the burden of 

WBDOs. 

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Legionnaires’ disease in cities using monochloramine versus other 

water disinfectants. Infect Control Hosp Epidemiol 2003;24:569–4. 

54. Phares CR, Russell E, Thigpen MC, et al. Legionnaires’ disease among 

residents of a long-term care facility: The sentinel event in a community outbreak. Am J Infect Control 2007;35:319–3 

55. Cordell K, Green G, Betz C, Fly M, Stephens B. Recreation statistics 

update. Update Report No. 1, August 2004—participation rates for 

outdoor activities in 2004. Available at: http://www.srs.fs.usda.gov/ 

trends/RECUPDATES/recupdate0804.pdf. 

56. Boulware DR, Forgey WW, Martin WJ. Medical risks of wilderness 

hiking. Am J Med 2003;114:288–3. 

57. Boulware DR. Influence of hygiene on gastrointestinal illness among 

wilderness backpackers. J Travel Med 2004;11:27–33. 

58. Boulware DR. Gender differences among long-distance backpackers: 

a prospective study of women Appalachian Trail backpackers. Wilderness Environ Med 2004;15:175–80. 

59. Twombly SE, Schussman LC. Gender differences in illness and injury 

rates on wilderness backpacking trips. Wilderness Environ Med 1995;4: 

363–76. 

60. Gardner TB, Hill DR. Illness and injury among long-distance hikers 

on the Long Trail, Vermont. Wilderness Environ Med 2002;13:131–4. 

61. Crouse BJ, Josephs D. Health care needs of Appalachian trail hikers. 

J Fam Pract 1993;36:521–5. 

62. Welch TR. Evidence-based medicine in the wilderness: The safety of 

backcountry water. Wilderness Environ Med 2004;15:235–7. 
Vol. 57 / SS-9 Surveillance Summaries 63 

Appendix A 

Glossary of Definitions 

action level A specified concentration of a contaminant in water. If this concentration is reached or 

exceeded, certain actions (e.g., further treatment and monitoring) must be taken to comply 

with a drinking water regulation. 

agent See etiologic agent. 

aquifer A geologic formation or part of a formation (e.g., gravel, sand, or porous stone) that yields 

water to wells or springs. 

backflow A hydraulic condition caused by a difference in water pressure that causes nonpotable water 

or other liquid to enter the potable water system by either backpressure or backsiphonage. 

See cross-connection. 

backpressure A hydraulic condition that results when pressure from a customer’s water system (e.g., 

potentially nonpotable water) is higher than pressure in the public water system, resulting 

in backflow of water into the public water system. 

backsiphonage A hydraulic condition caused by negative or subatmospheric pressure within a water 

system, resulting in backflow. 

biofilm Microbial cells that adhere to a surface through a matrix of primarily polysaccharide materials in which they are encapsulated. Biofilms can grow on piping and surfaces of water 

systems and can be difficult to remove. They offer protection to microbes from disinfectants (e.g., chlorine) in the water. 

boil-water advisory A statement to the public advising that tap water must be boiled before drinking. 

bottled water Commercially produced bottled water. 

class A categorization given to waterborne disease and outbreaks (WBDOs) indicating to the 

strength of the epidemiologic and water-quality data implicating water as the source of the 

disease or outbreak (see Table 3). 

coliforms All aerobic and facultative anaerobic, gram-negative, nonspore-forming, rod-shaped bacteria that ferment lactose with gas formation within 48 hours at 95°F (35°C). Coliforms are 

mostly harmless bacteria that live in soil and water as well as the gut of humans and animals. 

community water system A public water system that has at least 15 service connections used by year-round residents 

or that regularly serves at least 25-year-round residents. The system might be owned by a 

private or public entity providing water to a community, subdivision, or mobile home park. 

cross-connection Any actual or potential connection between a drinking water supply and a possible source 

of contamination or pollution (i.e., nonpotable water). Under this condition, contaminated water might flow back into the drinking water system. See backflow. 

deficiency An antecedent event or situation contributing to the occurrence of a waterborne disease or 

outbreak. 

dermatitis Inflammation of the skin. In this report, the term dermatitis is used to denote a broad 

category of skin-related symptoms (e.g., folliculitis, cellulitis, chemical burns, or rash). 
64 MMWR September 12, 2008 

disinfection A treatment that kills microorganisms (e.g., bacteria, viruses, and protozoa); in water treatment, a chemical (commonly chlorine, chloramine, or ozone) or physical process (e.g., 

ultraviolet light) may be used. 

disinfection by-products Chemicals formed in water by the reaction between organic matter and other waste products and disinfectants. 

distribution system Water pipes, storage reservoirs, tanks, and other means used to deliver drinking water to 

consumers or to store finished water before delivery to a customer. In community water 

systems, the distribution system is under the jurisdiction of a water utility and ends at the 

water meter or at the customer’s property line (if the system is not metered). In noncommunity and nonpublic individual water systems, the distribution system ends at the point 

where water enters the building or house. See plumbing. 

etiologic agent The pathogen, chemical, or toxin causing a waterborne disease or outbreak. Infectious etiologic agents are bacteria, parasites, viruses, or fungi. 

fecal coliforms Coliform bacteria that grow and ferment lactose to produce gas at 112.1°F (44.5°C) in 

<24 hours. These bacteria are associated with human and animal wastes, and their presence 

in water might be an indication of recent sewage or animal waste contamination. 

filtration In water treatment, the process of passing water through one or more permeable membranes or media of small diameter (e.g., sand, anthracite, and diatomaceous earth) to 

remove suspended particles from the water. Filters might be effective in removing pathogens, depending on the type and operation. 

finished water The water (e.g., drinking water) delivered to the distribution system after treatment, if any. 

free chlorine The chlorine in water that is not combined with other constituents, therefore, serving as an 

effective disinfectant (also referred to as free available chlorine and residual chlorine). 

ground water Water that is contained in interconnected pores in an aquifer. 

ground water system A system that uses water extracted from an aquifer (i.e., a well or spring) as its source. 

ground water under the direct As defined by the U.S. Environmental Protection Agency (EPA), any water beneath the 

influence of surface water surface of the ground with substantial occurrence of insects or other macrooganisms, algae, 

or large-diameter pathogens (e.g., Giardia intestinalis or Cryptosporidium), or substantial and 

relatively rapid shifts in water characteristics (e.g., turbidity, temperature, conductivity, or 

pH) that closely correlate with climatologic or surface water conditions. Direct influence must 

be determined for individual sources in accordance with criteria established by the state. 

individual water system A water system that does not meet the EPA definition for a public water system. The system 

might serve a single family or farm not having access to a public water system, or it might 

regularly serve as many as 24 persons or 14 connections. States are responsible for regulating these water systems. 

karst aquifer An aquifer characterized by water-soluble limestone and similar rocks in which fractures or 

cracks have been widened by the dissolution of the carbonate rocks by ground water; the 

aquifer might contain sinkholes, tunnels, or even caves. 

maximum contaminant level The maximum permissible concentration (i.e., level) of a contaminant in water supplied to 

any user of a public water system. 
Vol. 57 / SS-9 Surveillance Summaries 65 

mixed-agent outbreak More than one type of etiologic agent is identified in clinical specimens from affected persons, and each etiologic agent is found in more than 5% of positive clinical specimens (e.g., 

an outbreak with Giardia spp. [parasites] and Salmonella spp. [bacteria] with each agent 

identified in >5% of stool specimens). 

mixed-illness outbreak More than one type of illness is reported by more than 50% of patients in a single outbreak 

(e.g., a combination of gastroenteritis and dermatitis). 

mixed-source outbreak More than one type of source water is implicated in the outbreak (e.g., a combination of 

ground water and surface water). 

mixed-system outbreak More than one type of water system is implicated in the outbreak (e.g., a combination of 

noncommunity and individual water systems). 

noncommunity water system A public water system that is not a community system; it does not serve year-round residents. There are two types: transient and nontransient noncommunity systems. 

nontransient noncommunity A public water system that is not a community system and that regularly serves at least 25 of 

water system the same persons for more than 6 months per year but not year-round (e.g., a school, a 

factory, or a business with its own water supply). 

plumbing Water pipes, storage reservoirs, tanks, and other means used to deliver drinking water to 

consumers inside buildings or houses or to store drinking water inside buildings or houses 

before consumption. In community water systems, the plumbing begins after the water 

utility’s water meter or at the property line (if the distribution system is not metered). In 

noncommunity and nonpublic individual water systems, the plumbing begins at the point 

where water enters the building or house. See distribution system. 

predominant illness The category of illness reported by at least 50% of ill respondents (e.g., gastroenteritis, 

dermatitis, or acute respiratory illness). When more than one illness category is reported for 

a single WBDO, they are listed together as predominant illnesses. These mixed illness 

WBDOs are analyzed separately from WBDOs with single illnesses. 

primary water exposure For use in this report, a classification used for the source of contaminated water not 

intended for drinking or contaminated water of unknown intent. 

public water system A system, classified as either a community water system or a noncommunity water system, 

that provides piped water to the public for human consumption and is regulated under the 

Safe Drinking Water Act. Such a system must have at least 15 service connections or regularly serve at least 25 persons daily for at least 60 days per year. 

raw water Surface water or ground water that has not been treated in any way. 

reservoir, impoundment An artificially maintained lake, created for the collection and storage of water. This body of 

water can be available as a source of raw water for drinking purposes and/or recreational 

use. In certain instances, a finished water storage facility in the distribution system might 

also be called a reservoir. 

setting Location where exposure to contaminated water occurred (e.g., restaurant, water park, or hotel). 

source water Untreated water (i.e., raw water) used to produce drinking water. 

surface water All water on the surface (e.g., lakes, rivers, reservoirs, ponds, and oceans) as distinguished 

from subsurface or ground water. 
66 MMWR September 12, 2008 

total coliforms Fecal and nonfecal coliforms that are detected by using a standard test. The extent to which 

total coliforms are present in water can indicate the general quality of that water and the 

likelihood that the water is fecally contaminated by animal and/or human sources. 

transient noncommunity A public water system that is not a community system and that does not regularly serve at 

water system least 25 of the same persons for more than 6 months per year. These systems provide water 

to places where persons do not remain for long periods (e.g., restaurants, campgrounds, 

highway rest stations, or parks with their own public water systems). 

untreated water Surface water or ground water that has not been treated in any way (i.e., raw water). 

water not intended for drinking Water that has not been treated for human consumption in conformance with EPA drinking water standards and that is provided for uses other than for drinking. This might 

include water used in occupational settings; lakes, springs, and creeks used as drinking 

water by campers and boaters; irrigation water; and other nonpotable water sources with or 

without taps but does not include exposure to recreational water or flood water. 

water of unknown intent The information about the water is insufficient to determine for what purpose it is being 

provided or used and whether is has been treated for human consumption in conformance 

with EPA drinking water standards. 

water system A system for the provision of water for human consumption through pipes or other constructed conduits. This includes any collection, treatment, storage, and distribution facilities used primarily in connection with such a system. 
Vol. 57 / SS-9	 Surveillance Summaries 67 

Appendix B 

Descriptions of Selected Waterborne Disease Outbreaks Associated
 

with Drinking Water, Water Not Intended for Drinking,
 

and Water of Unknown Intent
 

State in No. of 

which WBDO cases 

Date occurred Etiologic agent (deaths) Description of WBDO 

Bacteria 

February 2006 Indiana Campylobacter spp. 32	 Thirty-two county residents who developed gastrointestinal illness 

were included in a case-control study that implicated municipal water 

as the source of infection. Seven of nine people who provided stool 

specimens tested positive for Campylobacter species; and routine 

water samples from the treatment facility tested positive for total 

coliforms and Escherichia coli at the time of the outbreak. The 

investigation determined that a chlorinator had malfunctioned before 

the outbreak, resulting in inadequate chlorination of the water supply, 

and that cross-contamination also might have occurred when a new 

water main was pressure-tested with non-potable water. 

May 2005 Oregon Escherichia coli O157:H7, 60	 Attendees of an outdoor school program at a camp developed 

C. jejuni, and E. coli O145 gastrointestinal illness with a median duration of four days. Stool 

samples were collected from 57 cases. Nine persons tested positive 

for E. coli O157:H7, three persons tested positive for C. jejuni, two 

persons tested positive for E. coli O145; and three persons tested 

positive for both E. coli O157:H7 and C. jejuni. The camp was required 

to upgrade the surface water-treatment system, which was suspected 

of providing inadequate treatment after heavy rainfall conditions. Raw 

water tested positive for fecal coliforms and E. coli approximately 

1 week after the first case-patient became ill. 

May 2005 South Dakota Legionella pneumophila 18 (1) Eighteen confirmed cases of Legionnaires’ disease were reported 

serogroup 1 over a 5-month period in Rapid City, South Dakota. An investigation, 

including a case-control study and environmental sampling, was 

conducted. A small, decorative fountain lacking obvious aerosolgenerating capacity was implicated. Clinical and environmental 

L. pneumophila serogroup 1 Benidorm isolates had identical 

sequence-based typing (SBT) patterns. (Source: O’Loughlin RE, 

Kightlinger L, Werpy, M, et al. Restaurant outbreak of Legionnaires’ 

disease associated with a decorative fountain: an environmental 

and case control study. BMC Infect Dis 2007;7:93). 

April 2006 Texas L. pneumophila serogroup 1 10 (3)	 Ten confirmed cases of Legionnaires’ disease, diagnosed by urine 

antigen and culture, were reported during spring 2005 after exposure 

to a hospital in San Antonio, Texas. The potable hot water supply of 

the newly constructed and recently opened inpatient building was 

determined to be the most likely source of the outbreak. Multiple 

L. pneumophila serogroup 1 strains were identified from environmental 

isolates taken from the hospital building; one previously unreported 

environmental strain matched a case-patient isolate. 

May 2002 Louisiana Pseudomonas aeruginosa 27	 Thirty-eight employees at a cardboard box manufacturing facility were 

surveyed regarding recent dermatologic symptoms. Twenty-seven 

employees reported rashes that were suspected to be work-related and 

were consistent with P. aeruginosa infection. The facility had recently 

switched to a closed-water system. Water used in manufacturing 

processes and cleaning was treated and re-used as plant process 

water. Water samples from multiple sites using this water contained 

high concentrations of P. aeruginosa. Contributing factors noted from 

the water samples included elevated water temperatures, high organic 

content, elevated pH levels and varying disinfectant levels. The 

observation was made that certain areas of the water system were 

accessed substantially less frequently than others and that the ability of 

Pseudomonas to produce biofilms in hoses or pipes might have limited 

the effectiveness of the treatment methods. (Source: Hewitt DJ., et al. 

Industrial Pseudomonas folliculitis. Am J Ind Med 2006; 49:895–9). 
68 MMWR September 12, 2008 

State in No. of 

which WBDO cases 

Date occurred Etiologic agent (deaths) Description of WBDO 

Viruses 

July 2006 North Carolina Hepatitis A 16 Private property owners allowed travelers to stay on their property and 

provided drinking water for public use. The drinking water source for 

the house and the camping area and the water supply for a limited 

amount of fruits and vegetables was a spring that the owner had 

excavated. Water was directed into a plastic reservoir above the 

spring. Untreated water was pumped to the house through a series of 

pipes and delivered to the downhill camping area through an overflow 

hose. Water from a spigot from outside the house tested positive for 

fecal coliforms, E. coli, and hepatitis A. The septic tank located directly 

upstream from the spring was considered a possible source of water 

contamination. 

July 2006 Maryland Norovirus G1 148 Attendees of a camp developed gastrointestinal illness. Participants 

were from England, Canada, Australia, Sweden, and the United States 

(i.e., California, Connecticut, Delaware, Indiana, Illinois, Massachusetts, Maryland, Michigan, New Jersey, New York, and Pennsylvania). 

Ten persons submitted stool samples, eight of which tested positive 

for norovirus G1. General concerns included toilet facilities with 

plumbing deficiencies and limited handwashing stations throughout 

the camp. The water distribution system did not contain a detectable 

level of chlorine. Nine of ten water samples from garden hoses used to 

provide drinking water contained total coliforms and E. coli. Well 

construction deficiencies were noted (e.g., absence of backflowprevention devices on the pool bath house water heaters and on water 

distribution lines to the latrines). The well storage tank and latrine 

wastewater samples contained Norovirus G1; tracer dye added to 

latrines was detected in the well. 

Parasites 

August 2005 California Giardia intestinalis 3 A child’s condition was diagnosed as laboratory-confirmed giardiasis, 

and a sibling and parent had clinically compatible symptoms. Canal 

water was piped into a private residence and used for bathing, 

dishwashing, housecleaning and laundry. Accidental ingestion of 

contaminated canal water was suspected. 

May 2006 Colorado G. intestinalis 6 Participants in a school trip to a state park became ill with gastrointestinal symptoms after consuming inadequately treated river water that 

was not intended for drinking. Treatment methods included the 

addition of iodine; filtration; and boiling. No one treatment method was 

used by the entire group (n=26) and variations in practice were 

observed among individuals who used each treatment method. 

Mixed Agents 

June 2006 Wyoming Norovirus G1, Norovirus G2, 139 Attendees of four week-long camps at a seasonal camp site experienced 

C. jejuni gastrointestinal illness. Investigators concluded that the camp’s two 

wells, which were drilled into fractured rock aquifers, may have been 

contaminated by raw sewage released from the main septic system. 

Water from the wells repeatedly tested positive for fecal and total 

coliforms; a septic tank sample tested positive for Norovirus G1 and 

G2. The main tank was documented as poorly located, at capacity and 

not meeting the state’s recommended standards for size or type of 

construction at the time of the outbreak. Well water was not filtered or 

chlorinated prior to consumption. (Source: CDC, Gastroenteritis 

among attendees at a summer camp—Wyoming, June-July 2006. 

MMWR 2007;56(15):368-370) 
Vol. 57 / SS-9	 Surveillance Summaries 69 

State in No. of 

which WBDO cases 

Date occurred Etiologic agent (deaths) Description of WBDO 

Unidentified 

August 2006 New York Norovirus suspected 16	 Visitors to a bed and breakfast, the owner and his daughter, developed gastrointestinal illness. The incubation period and duration of 

illness and symptoms were consistent with norovirus infection. The 

bed and breakfast had its own well and onsite wastewater disposal 

system, which were located in close proximity. A well water sample 

was positive for E. coli and might have been contaminated from a 

poorly maintained, leaking sewage system used by nearby cottages. 

Year-round residents used onsite septic systems or alternate disposal 

methods for wastewater when the seasonal system was turned off. 

The geology of the area was primarily fractured bedrock; contamination of the well likely resulted from waste that was released by the 

leaking seasonal sewage system or onsite wastewater systems, which 

then traveled through the rock until it reached the groundwater supply. 
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