### Surveillance Summaries October 22, 2004 / Vol. 53 / No. SS-8



## depar tment of health and human ser vices
Centers for Disease Control and Prevention 

# Morbidity and Mortality Weekly Report



# Title Surveillance for Waterborne-Disease Outbreaks Associated with Recreational Water — United States, 2001–2002

and

Surveillance for Waterborne-Disease Outbreaks Associated with Drinking Water — United States, 2001–2002**MMWR**

CONTENTS

Surveillance for Waterborne-Disease Outbreaks

Associated with Recreational Water — United States,

2001–2002 ..................................................................... 1
Introduction ......................................................................... 2 Background ......................................................................... 2
Methods .............................................................................. 2
Results ................................................................................. 4

Discussion ........................................................................... 9
Conclusion ........................................................................ 13 Acknowledgments ............................................................. 14
References ......................................................................... 14 Appendix ........................................................................... 16 Glossary ............................................................................ 20

Surveillance for Waterborne-Disease Outbreaks

Associated with Drinking Water — United States,

2001–2002 ................................................................... 23
Introduction ....................................................................... 24 Background ....................................................................... 24
Methods ............................................................................ 25
Results ............................................................................... 27

Discussion ......................................................................... 34
Conclusion ........................................................................ 38 Acknowledgments ............................................................. 38
References ......................................................................... 38 Appendix ........................................................................... 40 Glossary ............................................................................ 44 SUGGESTED CITATION General: Cen ters for Disease Control and Prevention. Surveillance for waterborne-disease outbreaks associated with recreational water — United States,2001–2002 and Surveillance for waterbornedisease outbreaks associated with drinking water — United States, 2001–2002. In: Surveillance Summaries, October 22, 2004. MMWR 2004:53(No. SS-8). Specific: [Author(s)]. [Title of particular article]. In: Surveillance Summaries, October 22, 2004. MMWR 2004;53(No. SS-8):[inclusive page numbers]. The MMWR series of publications is published by the Coordinating Center for Health Information and Service (Proposed), Centers for Disease Control and Prevention (CDC), U.S. Department of Health and Human Services, Atlanta, GA 30333.

Centers for Disease Control and Prevention Julie L. Gerberding, M.D., M.P.H. Director
Dixie E. Snider, M.D., M.P.H. ( Acting ) Chief of Science Tanja Popovic, M.D., Ph.D. ( Acting ) Associate Director for Science Coordinating Center for Health Information and Service (Proposed) James S. Marks, M.D., M.P.H. ( Acting ) Director John W. Ward, M.D. Editor, MMWR Series
Suzanne M. Hewitt, M.P.A. Managing Editor, MMWR Series C. Kay Smith-Akin, M.Ed. Lead Technical Writer/Editor

Jeffrey D. Sokolow, M.A. Project Editor Beverly J. Holland Lead Visual Information Specialist Lynda G. Cupell Malbea A. LaPete Visual Information Specialists

Kim L. Bright, M.B.A. Quang M. Doan, M.B.A. Erica R. Shaver Information Technology Specialists**Vol. 53 / SS-8 Surveillance Summaries 1**

Corresponding author: Michael J. Beach, Ph.D., Epidemiologist, CDC/ NCID/DPD, 1600 Clifton Rd., NE, MS F-22, Atlanta, GA 30341; Fax: 770-488-7761; E-mail: mjb3@cdc.gov.



# Surveillance for Waterborne-Disease Outbreaks Associated with Recreational Water — United States, 2001–2002

Jonathan S. Yoder, M.P.H., M.S.W., 1,2 Brian G. Blackburn, M.D., 2,3 Gunther F. Craun, M.P.H., 4 Vincent Hill, Ph.D., 2 Deborah A. Levy, Ph.D., 5 Nora Chen, Sc.M., 1 Sherline H. Lee, M.P.H., 5 Rebecca L. Calderon, Ph.D., 6 Michael J. Beach, Ph.D. 2
1 Public Health Prevention Service, Epidemiology Program Office, CDC; 2 Division of Parasitic Diseases, National Center for Infectious Diseases, CDC; 3Epidemic Intelligence Service, Epidemiology Program Office, CDC; 4 Gunther F. Craun and Associates, Staunton, Virginia; 5 Division of Healthcare Quality and Promotion, National Center for Infectious Diseases, CDC; 6 U.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 andTerritorial Epidemiologists have maintained a collaborative surveillance system for collecting and periodically reporting data related to occurrences and causes of waterborne-disease outbreaks (WBDOs) related to drinking water; tabulation of recreational water-associated outbreaks was added to the survillance system in 1978. This surveillance system is the primary source of data concerning the scope and effects of waterborne disease outbreaks on persons in the United States

. Reporting Period Covered: This summary includes data on WBDOs associated with recreational water that occurred during January 2001–December 2002 and on a previously unreported outbreak that occurred during 1998. Description of the System: Public health departments in the states, territories, localities, and the Freely Associated States are primarily responsible for detecting and investigating WBDOs and voluntarily reporting them to CDC on astandard form. The surveillance system includes data for outbreaks associated with both drinking water and recreational water; only outbreaks associated with recreational water are reported in this summary.
Results: During 2001–2002, a total of 65 WBDOs associated with recreational water were reported by 23 states. These 65 outbreaks caused illness among an estimated 2,536 persons; 61 persons were hospitalized, eight of whom died. This is the largest number of recreational water-associated outbreaks to occur since reporting began in 1978; the number of recreational water-associated outbreaks has increased significantly during this period (p<0.01). Of these 65 outbreaks, 30 (46.2%) involved gastroenteritis. The etiologic agent was identified in 23 (76.7%) of these 30 outbreaks;18 (60.0%) of the 30 were associated with swimming or wading pools. Eight (12.3%) of the 65 recreational waterassociated disease outbreaks were attributed to single cases of primary amebic meningoencephalitis caused by Naegleria fowleri ; all eight cases were fatal and were associated with swimming in a lake (n = seven; 87.5%) or river (n = one; 12.5%). Of the 65 outbreaks, 21 (32.3%) involved dermatitis; 20 (95.2%) of these 21 outbreaks were associated with spas or pools. In addition, one outbreak of Pontiac fever associated with a spa was reported to CDC. Four (6.1%) of the 65 outbreaks involved acute respiratory illness associated with chemical exposure at pools. Interpretation: The 30 outbreaks involving gastroenteritis comprised the largest proportion of recreational waterassociated outbreaks during this reporting period. These outbreaks were associated most frequently with Cryptosporidium (50.0%) in treated water venues and with toxigenic Escherichia coli (25.0%) and norovirus (25.0%) in freshwater venues. The increase in the number of outbreaks since 1993 could reflect improved surveillance and reporting at the local and state level, a true increase in the number of WBDOs, or a combination of these factors.
Public Health Action: CDC uses surveillance data to identify the etiologic agents, types of aquatics venues, watertreatment systems, and deficiencies associated with outbreaks and to evaluate the adequacy of efforts (e.g., regulations and public awareness activities) for providing safe recreational water. Surveillance data are also used to establish public health prevention priorities, which might lead to improved water-quality regulations at the local, state, and federal levels.**2 MMWR October 22, 2004**



## Introduction During 1920–1970, statistical data regarding U.S.waterborne-disease outbreaks (WBDOs) 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 maintained a collaborative surveillance system that tracks the occurrences and causes of WBDOs associated with drinking water; tabulation of recreational water-associated outbreaks was added to the surveillance system in 1978 (2–7). The surveillance system includes data regarding outbreaks associated with drinking water, recreational water, and other types of water exposures. This MMWR Surveillance Summary includes data on recreational water-associated outbreaks that occurred during 2001–2002 and for a previously unreported outbreak that occurred in 1998. Data on drinking water-associated outbreaks are presented in a separate MMWR Surveillance Summary ( 8). These surveillance activities are intended to 1) characterize the epidemiology of WBDOs; 2) identify changing trends in the etiologic agents that caused WBDOs and determine why the outbreaks occurred; 3) encourage public health personnel to detect and investigate WBDOs; and 4) foster collaborationamong local, state, federal, and international agencies on initiatives to prevent waterborne disease transmission. Dataobtained through this surveillance system are useful for identifying major deficiencies in the provision of safe recreationalwater. Surveillance information can influence prevention recommendations and research priorities and lead to improved water-quality regulations. However, the statistics reported inthis surveillance summary represent only a portion of the burden of illness associated with recreational water exposure. The surveillance information does not include endemic waterborne disease risks, nor are reliable estimates available of the number of unrecognized WBDOs and associated cases of illness.



## Background

Regulation of Recreational Water

State and local governments establish and enforce regulations to protect recreational water against naturally occurringor human-made contaminants. Standards for operating, disinfecting, and filtering public swimming and wading pools are regulated by state and local health departments and, as aresult, vary throughout the United States. In 1986, EPA published guidelines for microbiologic water quality for recreational freshwater (e.g., lakes and rivers) and marine water ( 9). For freshwater, the guideline recommends that the * 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.

### monthly geometric mean water-quality indicator concentration be <33 CFU/100 mL for enterococci or <126 CFU/100 mL for Escherichia coli . For marine water, the guideline recommends that the monthly geometric mean water-quality indicator concentration be <35 CFU/100 mL enterococci. States have latitude regarding their guidelines or regulations and can post warning signs to alert potential bathers untilwater quality improves. Unlike treated venues, in which disinfection can be used to address the majority of problems with the microbiologic quality of water, contaminated freshwater can require weeks or months to improve or return to normal. However, pools in treated venues might need to be closed until the water has been adequately treated and filtered or the pool drained and refilled to remove protozoan contamination. Prompt identification of potential sources of contamination and remedial action is necessary to return bathing water to an appropriate quality for recreational use.

EPA’s Action Plan for Beaches and Recreational Waters (Beach Watch) was developed as part of the Clean Water Action Plan (http://www.cleanwater.gov). The intent of BeachWatch is to assist state, tribal, and local authorities in strengthening and extending programs that protect users of fresh and marine recreational waters. As part of the Beaches Act of 2000,the U.S. Congress directed EPA to develop a new set of guidelines for recreational water based on new water-quality indicators. In 2002, EPA, in collaboration with CDC, began conducting a series of epidemiologic studies at fresh and marine water recreational beaches in the United States. The National Epidemiologic and Environmental Assessment of Recreational (NEEAR) Water Study (available at http:// www.epa.gov/nerlcwww/neearnerl.htm) is testing rapid new water-quality methods that produce results in <2 hours and is correlating these indicators with health effects amongbeachgoers. The results will be used to develop new EPA waterquality guidelines for freshwater and marine water use.



## Methods

Data Sources

Public health departments in the states, territories, localities, and the Freely Associated States* (FAS) have primary responsibility for detecting and investigating WBDOs, which they report voluntarily to CDC by using a standard form (CDC form 52.12, available at http://www.cdc.gov/ healthyswimming/downloads/cdc_5212_waterborne.pdf ).**Vol. 53 / SS-8 Surveillance Summaries 3**

† Additional terms are defined in the Glossary. 

### The form solicits data on characteristics of the outbreak,including person, place, time, and location; results from epidemiologic studies conducted; specimen and water sample testing; and other factors potentially contributing to the outbreak (e.g., environmental concerns, disinfection, and filtration[Glossary]). CDC annually requests reports from state, territorial, and FAS epidemiologists or persons designated as WBDO surveillance coordinators. Numeric and text data are abstracted from the outbreak form and supporting documents and entered into a database for analysis.



## Definitions †



### The unit of analysis for the WBDO surveillance system is an outbreak, not an individual case of a waterborne disease.Two criteria must be met for an event to be defined as a recreational water-associated disease outbreak. First, >2 persons must have experienced a similar illness after exposure to wateror air encountered in a recreational water setting. This criterion is waived for single cases of laboratory-confirmed primary amebic meningoencephalitis (PAM), single cases of wound infections, and single cases of chemical poisoning if water-quality data indicate contamination by the chemical. Second, epidemiologic evidence must implicate recreational water or the recreational water setting as the probable source of the illness.

Recreational settings include swimming pools, wading pools, whirlpools, hot tubs, spas, waterparks, interactive fountains(Glossary), and fresh and marine surface waters. When outbreak causes are analyzed, outbreaks are separated by venue. Fresh and marine waters are considered untreated venues. Treated venues refer to the remaining settings; occasionally, aprivate pool or wading pool involved in an outbreak is a drainand-fill type with no additional disinfection or treatment. If primary cases (i.e., illness among persons exposed to contaminated water or air at a recreational water setting) and secondary cases (i.e., illness among persons who became ill after contact with a person with a primary case) are distinguished on the outbreak report form, only primary cases are included in the total number of cases. If both actual and estimated casecounts are included on the outbreak report form, the estimated case count may be used if the population was sampled randomly or the estimated count was calculated by applying the attack rate to a standardized population.



## Outbreak Classification

WBDOs reported to the surveillance system are classified according to the strength of the evidence implicating water as the vehicle of transmission (Table 1). The classification scheme(i.e., Classes I–IV) is based on the epidemiologic and waterquality data provided on the outbreak report form. Epidemiologic data are weighted more than water-quality data.Although outbreaks without water-quality data might be included in this summary, reports that lack epidemiologic datawere excluded. Outbreaks of dermatitis, PAM, wound infections, or chemical poisonings are not classified according tothis scheme. Weighting of epidemiologic data does not preclude the relative importance of both types of data. The purpose of the outbreak system is not only to implicate water asthe vehicle for the outbreak but also to understand the circumstances and system breakdowns that led to the outbreak.

A classification of I indicates that adequate epidemiologic and water-quality data were reported (Table 1). However, the classification does not necessarily imply that an investigation was conducted optimally, nor does a classification of II, III,or IV imply that an investigation was inadequate or incomplete. Outbreaks and the resulting investigations occur under different circumstances, and not all outbreaks can or should be rigorously investigated. In addition, outbreaks that affect fewer persons are more likely to receive a classification of III

**TABLE 1. Classification of investigations of waterborne-disease outbreaks — United States Class Epidemiologic data Water-quality data** 

I

II

III

IV Adequate Data were 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 Historic information or laboratory data (e.g., the history that a chlorinator malfunctioned or the filter system broke, no detectable free-chlorine residual, or the presence of fecal indicator organisms in the water)

Not provided or inadequate (e.g., stating that a lake was

crowded)

Provided and adequate

Not provided or inadequate**4 MMWR October 22, 2004**

**TABLE 2. Waterborne-disease outbreaks of gastroenteritis (n = 12) associated with recreational water — United States, 2001**
**No. of cases** **State Month Class* Etiologic agent (n = 782) Source Setting**
Colorado Jul III Shigella sonnei 33 Interactive fountain Community Iowa Jun I S. sonnei 45 Wading pool Public park Illinois Jul I Cryptosporidium hominis † 358 Pool Waterpark Minnesota Jul III Escherichia coli O157:H7 § 20 Lake Public beach Minnesota Jul IV Norovirus 40 Lake Public beach Minnesota Aug IV E. coli O26:NM 4 Lake Community park Nebraska Jul IV Cryptosporidium species 157 Pools Community Nebraska Jul IV Cryptosporidium species 21 Pool Community New Hampshire Aug III AGI ¶ ** 42 Lake State park Oregon May IV AGI 15 Pool Lodge South Carolina Jul I E. coli O157:H7 45 Lake State park Wyoming Aug III Cryptosporidium species 2 Flow-through pool/hot spring †† State park
* On the basis of epidemiologic and water-quality data provided on CDC form 52.12. † The species of Cryptosporidium that infects humans and monkeys ( **Source:** Xiao L, Fayer R, Ryan U, Upton SJ. Cryptosporidium taxonomy: recent advances and implications for public health. Clin Microbiol Rev 2004;17:72–97). § Counted as an E.coli O157:H7 outbreak in all statistics. Ten persons had stool specimens that tested positive for E.coli O157:H7, and one person had a stool

specimen that tested positive for Campylobacter jejuni

. ¶ Acute gastrointestinal illness of unknown etiology.

** Oscillatoria was isolated from the lake water in high concentrations, which is consistent with clinical symptoms. †† Counted as freshwater venue in statistics.

### rather than I because of the relatively limited sample size available for analysis.

For the reporting period 2001–2002, WBDOs associated with drinking water and with recreational water are reported separately for the first time. The MMWR Surveillance Summary for drinking water-associated outbreaks ( 8) includesWBDOs related to drinking water and occupational exposures as defined in the methods section of that summary. This MMWR Surveillance Summary includes only outbreaks related to recreational water.

Although outbreaks of Pontiac fever have been included in previous MMWR Surveillance Summaries , this summary is the first to include outbreaks of Legionnaires disease (LD). Because nearly all outbreaks caused by Legionella species share characteristics that are distinct from other types of WBDOs, all Legionella outbreaks have been compiled into a single table in the drinking water-associated outbreak MMWR Surveillance Summary ( 8) that identifies the presumed primary use of the water implicated in the outbreak. Although all Legionella outbreaks are listed in that table, those related to recreational water exposure are discussed in this summary. Outbreaks of LD that occurred in association with water primarily intended for drinking or occupational use are discussed in the summary of drinking water-associated outbreaks ( 8).



## Results During 2001–2002, a total of 65 outbreaks (30 during 2001 and 35 during 2002) associated with recreational water were reported by 23 states (Tables 2–7). (Selected case descriptions are provided in the Appendix). These 65 outbreaks caused illness among 2,536 persons, resulting in 61 hospitalizationsand eight deaths. Of the 65 outbreaks, 30 (46.2%) were outbreaks of gastrointestinal illness (Tables 2 and 3); 21 (32.3%) were outbreaks of dermatitis (Table 4); eight (12.3%) wereoutbreaks of meningoencephalitis; and six (9.2%) were outbreaks of acute respiratory illness (including one of unknown etiology, one of Pontiac fever, and four caused by chemical exposure) (Tables 5 and 6).

The median outbreak size was 15 persons (range: 1–767). Although outbreaks were distributed throughout the United States (Figure 1), Florida and Minnesota reported the largest number of outbreaks (seven and nine, respectively).

Outbreaks occurred throughout the calendar year (Figure 2) but peaked during warm weather months (May–August). Of the 30 outbreaks involving gastrointestinal illness, 23 (76.7%) occurred during the summer (June–August); the eight cases of PAM also occurred during June–August (Figure 2).

Of the 65 recreational water outbreaks, 21 (32.3%) were associated with fresh water and 44 (67.7%) with treated (e.g.,chlorinated) water (Table 7). Of the 30 outbreaks of gastroenteritis, 12 (40.0%) were associated with fresh or surface water and 18 (60%) with treated (e.g., chlorinated) water venues (Figure 3).


## Etiologic Agents

The infectious agent was identified or suspected in 53 (81.5%) of the 65 recreational water-associated outbreaks (Table 7). Of the 30 outbreaks involving gastroenteritis, 12 (40.0%) were caused by parasites, six (20.0%) by bacteria,**Vol. 53 / SS-8 Surveillance Summaries 5**

**TABLE 3. Waterborne-disease outbreaks of gastroenteritis (n = 18) associated with recreational water — United States, 2002**
**No. of cases** **State Month Class* Etiologic agent (n = 1,137) Source Setting**
Florida Jul I AGI † 7 Lake Public beach Florida Oct III AGI 3 Pool Apartment complex Georgia Jul III Cryptosporidium species 3 Wading pool Child care center Maine Jul IV Escherichia coli O157:H7 9 Wading pool Private home Maine Nov III AGI 33 Puddle School Massachusetts Jul II Cryptosporidium species 767 Pool Membership sport club Michigan Dec IV AGI 32 Pool Hotel/motel Minnesota Jun IV Norovirus 11 Lake Public beach Minnesota Mar II Norovirus 36 Pool Hotel/motel Minnesota Jul II Cryptosporidium species 52 Indoor pool Health club Minnesota Aug II Cryptosporidium species 41 Pool Hotel/motel Minnesota Aug II Cryptosporidium species 16 Pool Resort Oregon Aug II AGI 9 Pool Apartment complex Texas Aug IV Cryptosporidium hominis § 54 Wading pool Hotel/motel Wisconsin Mar IV Norovirus 15 Pool Hotel/motel Wisconsin Jul III Norovirus ¶ 44 Lake State park Wyoming May IV Cryptosporidium species 3 Lake Lake Wyoming Jul IV Giardia intestinalis 2 River River * On the basis of epidemiologic and water-quality data provided on CDC form 52.12. † Acute gastrointestinal illness of unknown etiology. § The species of Cryptosporidium that infects humans and monkeys ( **Source:** Xiao L, Fayer R, Ryan U, Upton SJ. Cryptosporidium taxonomy: recent advances and implications for public health. Clin Microbiol Rev 2004;17:72–97). ¶ Counted as a norovirus outbreak in all statistics. Two persons with primary cases had stool specimens tested; one person had a stool specimen that tested

positive for norovirus, and one person had a stool specimen that tested positive for Cryptosporidium. Stool specimens from two persons with secondary cases were tested; one person had a stool specimen that tested positive for norovirus, and one person had a stool specimen thattested positive for Shigella sonnei. Illness in persons with primary cases was most consistent with norovirus infection.

**TABLE 4. Waterborne-disease outbreaks of dermatitis (n = 21) associated with recreational water — United States, 2001–2002**
**No. of cases State Year Month Etiologic agent (n = 435) Source Setting** 

Alaska 2002 Feb Pseudomonas aeruginosa* † 110 Pool/spa Hotel/motel Alaska 2002 Feb P. aeruginosa § 3 Pool/spa Hotel/motel Colorado 2002 May P. aeruginosa † 12 Pool/spa Hotel/motel Florida 2001 Mar P. aeruginosa § 34 Pool Hotel/motel Florida 2001 Mar P. aeruginosa † 53 Spa Hotel/motel Florida 2001 Apr P. aeruginosa § 7 Spa Apartment complex Iowa 2002 Mar P. aeruginosa § 24 Pool/spa Hotel/motel Maine 2001 Feb P. aeruginosa § 21 Spa Hotel/motel Maryland 2001 Nov P. aeruginosa § 8 Spa Private residence Maryland 2002 Feb P. aeruginosa § 3 Spa Membership club Minnesota 2001 May P. aeruginosa * † 6 Spa Resort Nebraska 2001 Mar P. aeruginosa § 9 Pool/spa Hotel/motel Ohio 2002 Feb P. aeruginosa † 18 Spa Hotel/motel Ohio 2002 Mar P. aeruginosa * † 31 Pool/spa Hotel/motel Oregon 2002 Jul Avian schistosomes § 19 Lake Lake Pennsylvania 2001 May P. aeruginosa † 2 Spa Hotel/motel Pennsylvania 2001 May P. aeruginosa § 42 Spa Hotel/motel Pennsylvania 2001 May Bacillus species † 20 Spa Hotel/motel Pennsylvania 2001 Jun Staphylococcus species § 3 Spa Hotel/motel Washington 2001 Aug P. aeruginosa † 3 Spa Hotel/motel Wisconsin 2001 Nov P. aeruginosa § 7 Spa Hotel/motel * Laboratory-confirmed case. † Organism isolated from water. § Suspected etiology on the basis of clinical syndrome and setting.**6 MMWR October 22, 2004**

**TABLE 5. Waterborne-disease outbreaks of meningoencephalitis, acute respiratory infection, and Pontiac fever (n = 10) associate d**  **with recreational water — United States, 2001–2002**
**No. of cases** **State Year Month Class* Etiologic agent Illness (n = 80) Source Setting**

Florida 2002 Jul NA † Naegleria fowleri Meningoencephalitis 1 Lake Park Florida 2002 Jul NA N. fowleri Meningoencephalitis 1 Lake Lake Georgia 2002 Aug NA N. fowleri Meningoencephalitis 1 River River Georgia 2002 Jun IV ARI § Acute respiratory 4 Spa Private residence Illinois 2002 Aug I Legionella species ¶ ** Pontiac fever 68 Spa Hotel/motel Oklahoma 2001 Jun NA N. fowleri Meningoencephalitis 1 Lake Lake Texas 2001 Aug NA N. fowleri Meningoencephalitis 1 Lake Lake Texas 2001 Aug NA N. fowleri Meningoencephalitis 1 Lake Lake Texas 2001 Aug NA N. fowleri Meningoencephalitis 1 Lake Lake Texas 2002 Aug NA N. fowleri Meningoencephalitis 1 Lake Lake
* On the basis of epidemiologic and water-quality data provided on CDC form 52.12. † Not applicable. § Acute respiratory infection of unknown etiology; Legionella species suspected. ¶ Also listed in Table 2 in Blackburn B, Craun GF, Yoder JS, et al. Surveillance for waterborne-disease outbreaks associated with drinking water—United

States, 2001–2002. In: Surveillance Summaries (October 22, 2004). MMWR 2004;53(No. SS-8):23–45 but only counted in statistics p ertaining to this summary. ** The spa filter was positive for Legionella dumoffii

.

**TABLE 6. Waterborne-disease outbreaks involving chemical exposures* (n = 4) associated with recreational water — United** **States, 2001–2002**
**No. of cases State Year Month Etiologic agent Illness (n = 102) Source Setting**  Alaska 2002 Sep Chlorine gas Acute respiratory 30 Pool University Ohio 2002 Jun Chlorine gas Acute respiratory 20 Wave pool Waterpark West Virginia 2002 Oct Chloramines † Acute respiratory 32 Indoor pool Hotel/motel Wisconsin 2001 Sep Chloramines † Acute respiratory 20 Indoor pool School * On the basis of epidemiologic and water-quality data provided on CDC form 52.12. † Suspected etiology on the basis of clinical syndrome and setting.


### and five (16.7%) by viruses; the remaining seven (23.3%) were of unknown etiology (Figure 3) (Table 7). Cryptosporidiumspecies remained the most common cause of outbreaks associated with treated swimming water (50.0%), and toxigenic E. coliserotypes and norovirus were the most commonly identified causes (25.0% each) of outbreaks associated with fresh water exposure (Figure 3).

The etiologic agent was suspected or identified in 34 (97.1%) of the 35 nongastroenteritis-related recreational outbreaks: 18 were caused by Pseudomonas aeruginosa , eight by Naegleria fowleri , one by Legionella species, one by Bacillus species, one by Staphylococcus species, one by avian schistosomes, and four by chlorine-based pool chemicals (Tables 4–7). One outbreak of unknown etiology was consistent with Legionella species on the basis of observed symptoms resembling Pontiac fever and the epidemiologically implicated mode of transmission.

Gastroenteritis Outbreaks

Parasites. Of the 12 parasitic recreational water-associated outbreaks of gastroenteritis, 11 (91.6%) were caused by Cryptosporidium species, and one was caused by Giardia intestinalis . Nine (75.0%) of these 12 parasitic outbreaks occurred in chlorinated venues. During the 2001–2002 summer swim seasons, three outbreaks of Cryptosporidiumspecies occurred that were related to fecal contamination; each outbreak affected >100 persons.In July 2001, an outbreak occurred in a Nebraska community, causing 157 illnesses. In this outbreak, contamination was introduced into a wading pool by a fecal accident andsubsequently spread via infected swimmers to multiple community pools. At an Illinois waterpark (July 2001), 358 persons became ill with cryptosporidiosis after the introductionof fecal contamination into facility pools. A sustained outbreak of cryptosporidiosis (July 2002) at a Massachusetts health club sickened 767 persons. Epidemiologic evidence indicated that infections associated with pool use occurred throughout the summer, with transmission peaking during a heat wave in mid-August.

Bacteria. Six recreational water-associated outbreaks of gastroenteritis were attributed to bacterial pathogens, three of which were linked to freshwater sources. Twenty cases (Minnesota, July 2001) of E. coli O157:H7 occurred amongpersons who had visited a lakefront beach located in a metropolitan area. The environmental investigation at the lake identified high fecal coliform levels, and the beach was closed for**Vol. 53 / SS-8 Surveillance Summaries 7**

**TABLE 7. Waterborne-disease outbreaks (n = 65) associated with recreational water, by etiologic agent and type of water —**  **United States, 2001–2002 Type** 
**Treated Fresh Total Etiologic agent Outbreaks Cases Outbreaks Cases Outbreaks Cases** 

**Bacterial 24 571 3 69 27 640**

Pseudomonas aeruginosa 18* 393 0 0 **18 393** Escherichia coli (O157:H7, O26:NM) 1 9 3 † 69 **4 78** Shigella sonnei 2 78 0 0 **2 78** Bacillus species 1 20 0 0 **1 20** Legionella species 1 68 0 0 **1 68** Staphylococcus species 1300 **1 3 Parasitic 9 1,469 12 34 21 1,503** 

Cryptosporidium species 9 1,469 2 5 **11 1474** Naegleria fowleri 0088 **8 8** Giardia intestinalis 0012 **1 2** Avian schistosomes 0 0 1* 19 **1 19 Unknown**  **5 63 3 82 8 145**

AGI § 4 59 3 82 **7 141** ARI ¶ 1400 **1 4 Viruses 2 51 3**  **† 95 5 146** 

Norovirus 2 51 3 † 95 **5 146 Chemical 4 102 0 0 4 102** 

Chlorine gas 2 50 0 0 **2 50** Chloramines 2* 52 0 0 **2 52 Total 44 2,256 21 280 65 2,536**  **Percentage (67.7) (89.0) (32.3) (11.0) (100) (100)** * Includes outbreaks of suspected etiology on the basis of clinical syndrome and setting. † Includes one mixed-pathogen outbreak. § Acute gastrointestinal illness of unknown etiology. ¶ Acute respiratory illness of unknown etiology. 

### the rest of the season. Five of the ill persons subsequently reported attending child care centers during or shortly after their illness, and a secondary outbreak resulted.

Three bacterial outbreaks of gastroenteritis (two of Shigella sonnei and one of E. coli O157:H7) occurred in venues using chlorinated tap water with no additional disinfection. In June 2001, an outbreak of S. sonnei in Iowa affected 45 persons, and 24 secondary infections occurred ( 10 ). Illnesses were linked epidemiologically to use of a drain-and-fill municipal wading pool. The pool was filled each day with drinking water, had no recirculation or disinfection system, and was frequented by diaper-aged children. Pool water tested positive for fecal coliforms (Glossary) and E. coli . Subsequent to the outbreak, a communitywide outbreak of shigellosis involving multiple local child care centers occurred. Another outbreak (Maine, July 2002) affecting nine persons at a private home was caused by E. coli O157:H7 in a toddler wading pool. One child was hospitalized. The pool was filled with tap water but was not additionally treated (i.e., filtered or recirculated). High bather density and a fecal accident might have contributed to the outbreak. In July 2001 in Colorado, 33 persons were infected by S. sonnei after exposure to an interactive fountain, which was at sidewalk level with no barriers to public access. The fountain, which was used frequently for recreation, especiallyby young children, used chlorinated city water that was recirculated with no additional treatment. **FIGURE 1. Number of waterborne-disease outbreaks (n = 65) associated with recreational water, by state — United States,**  **2001–2002***

* Numbers are dependent on reporting and surveillance activities in

individual states and do not necessarily indicate that more outbreaks occur in a given state. No. of oubreaks No. of states

>4 5

3 7

2 4

1 7

0 27**8 MMWR October 22, 2004**

**FIGURE 3. Waterborne-disease outbreaks of gastroenteritis associated with recreational water, by etiologic agent and type of exposure — United States, 2001–2002** 

* Acute gastrointestinal illness of unknown etiology. † Includes one mixed pathogen outbreak. § Includes outbreaks of Escherichia coli O157:H7 and O26:NM. ¶ Includes two outbreaks of Cryptosporidium hominis

. Fresh water 40.0% Treated water 60.0%

Cryptosporidium species 16.7% E.coli § 25.0% AGI* 25.0%

Norovirus † 25.0% Etiologic agent in fresh water (n = 12)

Giardia intestinalis 8.3% Type of exposure (n = 30)

Cryptosporidium species ¶ 36.7%

Shigella sonnei 6.7% E. coli § 13.3% AGI* 23.3%

Norovirus †

16.7%

Etiologic agent in treated water (n = 18)

Cryptosporidium species ¶ 50.0% Giardia intestinalis 3.3%

AGI* 22.2%

Norovirus †

11.1% Etiologic agent (n = 30)

Shigella sonnei 11.1% E. coli O157:H7 5.6% 

### state park, and 22 secondary cases were reported among parkvisitors. Of the 44 persons with primary cases, 21 (49%) continued to use the beach and swim after illness onset. Althoughthe majority of illnesses were consistent with norovirus infection, the outbreak was attributed to three pathogens: norovirus, S. sonnei , and Cryptosporidium species. The county health department closed the beach to swimming after finding 2,419 E. coli CFU/100 mL in beach water samples. Water samples collected before the outbreak had not exceeded EPA’s 235 CFU/100 mL single-sample maximum guideline. Althoughthe source of the fecal contamination was not identified, multiple sources were suspected; high levels of bacteria in Lake Michigan can also be affected by weather conditions and low lake levels. The same beach was closed on five other occasionsduring the summer when water samples exceeded the guideline; each closing occurred <48 hours after a rainfall event. This is the first documented outbreak associated with use of a Great Lakes beach since this surveillance system was created.

Two outbreaks of norovirus infection were associated withswimming pools. In one such outbreak, 36 persons (Minnesota, March 2002) associated with three youth sports teams became ill after swimming in a hotel pool and spa.

Other. During 2001–2002, seven recreational water outbreaks involving gastroenteritis of unknown etiology were reported, including four in swimming pools, two in lakes, and one in a water puddle. In one outbreak (New Hampshire, August 2001), 42 children became illwith nausea, vomiting, and diarrhea after swimming in a state park lake. Oscillatoria was isolated from the lake water in high concentrations, which was consistent with the clinical symptoms manifested. An estimated 33 childrenbecame ill (Maine, November 2001) after playing in a large puddle, an activity not usually associated with illness. The puddle was caused by an overflowingseptic tank and excessive rain; high levels of E. coli were identified in the water.
Nongastroenteritis Outbreaks

Dermatitis. During 2001–2002, a total of 21 outbreaks of dermatitis were identified (Table 4). An outbreak in Oregon during 2002 that sickened 19 persons was associated with swimming in freshwater lakes and rivers and was consistent with cercarial dermatitis (Glossary). **FIGURE 2. Number of waterborne-disease outbreaks (n = 65) associated with recreational water, by illness and month —**  **United States, 2001–2002**

* Acute respiratory illness, Pontiac fever, or chemical exposure. 0 2 4 6 8 10 12 14 16 18

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Other* Meningoencephalitis Dermatitis Gastroenteritis

2001–2002 Number of outbreaks



### Viruses. During 2001–2002, five recreational waterassociated outbreaks of gastroenteritis were attributed tonorovirus (Glossary), causing illness in 146 persons. An outbreak of gastroenteritis in July 2001 in Minnesota that affected 40 persons was linked to a community swimming beach at a lake. Epidemiologic evidence indicated that this waterborne outbreak might have been part of a larger communitywide norovirus outbreak occurring during that time. An outbreak (Wisconsin, July 2002) of 44 primary cases was reported among persons swimming at a Lake Michigan**Vol. 53 / SS-8 Surveillance Summaries 9**



### The 20 remaining outbreaks were associated with pool and spa use and affected 416 persons. P. aeruginosa was confirmed in water or filter samples from eight outbreaks, three of which also had a clinical isolate of P. aeruginosa . In the remaining 12 outbreaks, Pseudomonas was suspected on the basis of the clinical syndrome and setting. In eight dermatitis outbreaks,the affected persons (e.g., members of youth sports teams traveling for a tournament or persons attending birthday parties) were attending events at a hotel and used a hotel spa during the event.

In multiple outbreaks in Pennsylvania (May 2001), participants in a youth soccer tournament had folliculitis (Glossary), and >3 different local hotel spas were implicated. Although 64 cases were identified, officials estimated that >150 persons became ill. Determining the number of affected persons was difficult because players from other states participated in the tournament. Contributing factors to these outbreaks included inadequate spa maintenance, nonadherence to the bather load limit, and failure to shower before and after spa use.

Meningoencephalitis. Eight cases of laboratory-confirmed PAM attributed to N. fowleri occurred during 2001–2002 (Table 5). All eight persons died from infection after having summertime contact with lake or river water. In three cases, the infected person was reported to have had contact withsediment from the lake or river bottom while diving or stirring up the soil ( 11 ).

Chemical. During 2001–2002, four outbreaks that affected102 persons were attributed to chemical exposure in recreational water settings (Table 6). Two outbreaks that occurredin outdoor pool settings were attributed to buildup of chloramines (Glossary), a class of disinfection byproducts/irritants ( 12–14 ). In pools, chloramines result from the combination of chlorine used for disinfection and organic compounds (e.g., saliva, perspiration, urine, body oils) deposited in the water. Chloramines can accumulate in the pool water and volatilizeinto the air. In indoor pools with inadequate ventilation, levels can increase to the point that respiratory irritation occurs; contact with water with high levels can cause dermatitis and irritation of mucous membranes ( 12–14 ). In October 2002, a total of 32 hotel guests in West Virginia who were exposed to an indoor pool and surrounding area reported symptoms of cough, eye and throat irritation, and difficulty breathing. The proportion of exposed persons who became ill increased with duration of indoor pool air or water exposure. Illness was likely caused by the buildup of chloramines in the pool

area.

Two chemical outbreaks were related to respiratory exposures to chlorine gas at swimming pools. In Alaska (September 2002), a maintenance worker mistakenly mixed chlorine and hydrochloric acid, leading to the release of chlorine gas, and in Ohio (June 2002), workers failed to shut down the chlorine feed system during waterline repairs.

Other. One outbreak of acute respiratory illness identified as Pontiac fever (Illinois, 2002) sickened 68 persons and was linked epidemiologically to use of a hotel spa (Table 5).Another outbreak (Georgia, June 2002) involved acute respiratory infections of unknown etiology. Four persons affected in this outbreak reported symptoms that included nausea, headache, chills, and fever after bathing in a spa at a private residence. Although urine specimens were tested for L. pneumophila , no infectious agent was identified.


## Previously Unreported Outbreaks

A previously unreported recreational water-associated outbreak occurred in Colorado in June 1998. Five family members became ill with nontuberculous mycobacterial respiratory disease; two were hospitalized ( 15). Illness was linked epidemiologically and environmentally to an in-home spa exposure, both by contact and inhalation. Multiple species of nontuberculous mycobacteria were isolated from the spa water, including Mycobacterium aviumcomplex and M. fortuitum

. Inadequate disinfection levels, lack of monitoring of pH and disinfection levels, and having the spa inside the living areawere contributing factors to this outbreak. This type of spaassociated pneumonitis has been described previously ( 16 ).



## Discussion

Trends in Outbreak Reporting

The number of recreational water-associated outbreaks has increased significantly since 1993 (Pearson’s correlation = 0.77; p<0.01) and is at the highest 2-year level (65 outbreaks for 2001–2002, compared with 59 outbreaks for 1999–2000 [2 ]) since CDC began receiving such reports in 1978 (Figure 4).The increase since 1993 is also significant for reported outbreaks of gastrointestinal illness (Pearson’s correlation = 0.67; p = 0.034) (Figure 5) and for outbreaks of nongastrointestinal illness (Pearson’s correlation = 0.74; p = 0.014). Whether this reflects a true increase in the number of outbreaks or reflects increasing attendance at aquatics venues (e.g., waterparks, [ 17 ]), increased recognition of the potential health concerns associated with recreational water (which has led to improvedsurveillance and investigation), or a combination of these factors is unknown. Factors influencing the sensitivity of this reporting system have been discussed previously ( 2). The increased reporting of gastrointestinal illness outbreaks since 1993 might reflect a true increase in the number of outbreaks occurring. This is indicated because the reported increase is**10 MMWR October 22, 2004**

**FIGURE 5. Number of waterborne-disease outbreaks of gastroenteritis (n = 176) associated with recreational water,**  **by year — United States, 1978–2002**

0 5 10 15 20 25

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
Year Number of outbreaks

**FIGURE 6. Number of waterborne-disease outbreaks of gastroenteritis (n = 176) associated with recreational water, by water type — United States, 1978–2002** 

0 2 4 6 8 10 12 14 16 Treated Freshwater

Year Number of outbreaks

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

### associated primarily with treated venues (Figure 6) as a result of contamination of pool water by Cryptosporidium(Figure 7), reflecting the emergence of the naturally chlorine-resistant Cryptosporidiumas a human pathogen since 1980 ( 18). In contrast, the high numbers of outbreaks reported by Florida and Minnesota might be attributable to enhanced surveillance and investigative activities rather than to a higher incidence of WBDOs compared with other states.

One key limitation of the data collected as part of the WBDO surveillance system is that the information pertains only to disease outbreaks rather than endemic illness. The epidemiologic trends and water-quality concerns observed in outbreaks might not necessarily reflect or correspond with trends associated with endemic waterborne illness. To address this problem, EPA and CDC are collaborating on the NEEAR Water Study to assess the magnitude of waterborne illness associated with routine, nonoutbreak-associated exposure to marine and freshwater recreational areas.



## Gastroenteritis-Associated Outbreaks

Fecal contamination of recreational water that can lead to outbreaks of gastroenteritis occurs through different means. Because swimming is essentially communal bathing, rinsing of soiled bodies and fecal accidents from swimmers can causecontamination of the water. Unintentional ingestion of recreational water contaminated with pathogens can then lead to gastrointestinal illness, even in nonoutbreak settings ( 19,20 ).Fresh and marine waters are also subject to fecal contamination from point sources (i.e., sewage releases), watersheds (i.e., runoff from agricultural, forest, and residential areas), and floods. Wild and domestic animals, as well as infected humans, can be sources of certain pathogens, including Giardia intestinalis

, Cryptosporidium , and toxigenic E. coli

. Weather conditions (e.g., wind, rain, and drought) can also affect the water quality, and high air temperatures can cause overcrowding and decreased water quality in pools and lakes.

Of the 65 recreational WBDOsreported during 2001–2002, the largest proportion reported (46.2%) involved gastroenteritis, compared with 61.0% during 1999–2000 (2). As during the previous reporting period, Cryptosporidiumaccounted for the largest percentage of outbreaks involving **FIGURE 4. Number of waterborne-disease outbreaks (n = 445) associated with recreational water by year and illness —**  **United States, 1978–2002**

* Includes keratitis, conjunctivitis, otitis, bronchitis, meningitis, hepatitis,

leptospirosis, Pontiac fever, and acute respiratory illness. † Also includes data from report of ameba infections ( **Source:** Visvesvara

GS, Stehr-Green JK. Epidemiology of free-living ameba infections. J Protozool 1990;37:25S–33S). 0 5 10 15 20 25 30 35 40

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 Other*
Dermatitis Meningoencephalitis †
Gastroenteritis

Year Number of outbreaks**Vol. 53 / SS-8 Surveillance Summaries 11**



### gastroenteritis (36.7%) (Figure 3) (Table 7). Of the 30 outbreaks involving gastrointestinal illness, 18 (60.0%) occurred in treated systems (i.e., pools). In treated venues, 50% of the outbreaks were attributed to Cryptosporidium (Figure 3). During 1993–2002, Cryptosporidiumaccounted for >65% of outbreaks occurring in treated venues (Figure 7).

Unlike other organisms, which are more susceptible to the levels of chlorine typically maintained in a pool, Cryptosporidium oocysts (Glossary) are highly chlorineresistant and require increased levels of chlorine and longer contact times (Glossary) with chlorine for inactivation. Cryptosporidium can survive for days in public health– mandated chlorine concentrations required for pools (1–2 ppm free chlorine). Certain outbreak reports noted inadequate pool maintenance as a contributing factor to the outbreak. Although low chlorine levels are unlikely to have been the cause of cryptosporidiosis outbreaks, the deficiency serves to indicate deterioration of water quality caused by overcrowding or the introduction of fecal contamination.

The frequent reporting of low chlorine levels in outbreaks indicates a disturbing lack of awareness among pool operators concerning the role of chlorine and pH control as the major protective barrier against infectious disease transmission in pools. In addition, inadequate disinfectant levels in any pool increases the risk for transmission of chlorine-susceptible pathogens (e.g., E. coli O157:H7 and Shigella species) if an infected swimmer contaminates the pool. Analysis of >22,000 pool-inspection records indicated that the majority of pool inspections had >1 pool code violation for water quality, recirculation system, or pool management, and 8.3% of inspections resulted in immediate pool closure ( 21 ). This emphasizes the need for increased vigilance to ensure that pool operators and staff are appropriately trained regarding the need to follow guidelines (av ailable at http://www.cdc.gov/ healthyswimming/ poolstaff.htm) to prevent the spread of recreational water illnesses and to ensure proper pool maintenance (i.e., disinfection, pH control, and filtration) (22).

The treated-venue outbreaks of chlorine-susceptible pathogens (e.g., S. sonnei and E. coli O157:H7) reported in thissummary all occurred in pools that were not adequately chlorinated. Two S. sonnei outbreaks were in public venues (i.e.,an interactive fountain without water treatment and a drainand-fill wading pool), which underscores the need for health authorities and operators to be vigilant about the necessity for including disinfection and filtration in all designs for publicswimming venues (including interactive fountains and wading pools) that are easily used and accessed by the public, particularly young children. The outbreak of E. coli O157:H7occurred in a home wading pool with no disinfection or filtration. The use of tap water to fill these wading pools means that the water is essentially untreated upon filling (i.e., when unchlorinated tap water from a home well is used) or shortly thereafter (i.e., when chlorinated tap water is used, and the chlorine dissipates rapidly) and offers little protection against the spread of pathogens. Thus, these venues present a high risk for exposure if persons ill with diarrhea swim and fecal contamination occurs. These pools should be used with caution and, at a minimum, should be drained and cleaned after each use. Education of users should alert them to the potential for disease transmission and stress that children with diarrhea should refrain from swimming in them. Use of these pools in institutional settings (e.g., childcare centers that have substantial numbers of toddler and diaper-aged children) should be avoided.

Use of recreational water venues can lead to amplification of disease and tocommunitywide transmission. Communal use of recreational water makes it ideal for amplification of enteric illness circulating in communities. Whether **FIGURE 7. Waterborne-disease outbreaks of gastroenteritis associated with recreational water, by etiologic agent and type of exposure — United States, 1993–2002** 

* Acute gastrointestinal illness of unknown etiology. † Includes Escherichia coli O157:H7, E. coli O26:NM, and E. coli O121:H19. § Includes Shigella sonnei and Shigella flexneri

. ¶ These included outbreaks of Salmonella and Campylobacter

. Cryptosporidium

species 10.3% E.coli † 25.9% AGI* 25.9%

Norovirus 13.8% Etiologic agent in fresh water (n = 58)

Giardia intestinalis 8.6% Shigella § 15.5% Fresh water

47.5% Treated water 52.5% Type of exposure (n = 122)
Cryptosporidium species 39.3%

Shigella § 11.5% E. coli † 15.6%

AGI* 17.2%

Norovirus

9.0% Other 1.6% ¶ Etiologic agent (n = 122)

Giardia intestinalis 5.7%

Etiologic agent in treated water (n = 64)

Cryptosporidium

species 65.6%

AGI* 9.4% Norovirus 4.7% Other 3.1% ¶

E. coli O157:H7 6.3% Giardia intestinalis 3.1%

Shigella § 7.8%**12 MMWR October 22, 2004**



### swimming venues serve as the initial exposure event or anintermediary amplification mode for community enteric illness, public health officials might wish to alert pool operators, child care centers, schools, and other establishments that include recreational water facilities when increases in enteric illness are noted in the community. These community alerts would serve to increase awareness and improve vigilanceregarding maintenance and water-quality parameters (i.e., disinfection, pH levels, and filtration) needed to prevent further amplification of most enteric pathogens.

During 2001–2002, a total of 12 gastroenteritis outbreaks were reported after freshwater exposure. Certain outbreaksoccurred in beach areas that had substantial numbers of families bathing and swimming in the water. A common elementnoted in these reports was the presence of diaper-aged children in the water, diaper changing on the beach, and washingof young children in the water. Reports of infants and children swimming when they have diarrhea is a problem common to both freshwater systems and treated venues. Although health communication messages have been targeted in the past for treated venues, similar messages should be provided to those who swim in fresh or marine water venues. As part of itsBeaches Action Plan, EPA is developing guidelines and information for users of fresh and marine waters (available at http://www.epa.gov/waterscience/beaches).

Use of untreated geothermal or hot spring water in recreational venues should be examined closely by public health officials. In one outbreak of cryptosporidiosis (Wyoming, 2001), untreated hot spring water was used to fill flow-through swimming pools. Hot springs, which feature high levels ofminerals and elevated temperatures, are potentially ideal venues for pathogen growth (e.g., Naegleria, Acanthamoeba, and Legionella) or contamination by users with enteric illness. Two outbreaks of gastroenteritis have been reported previously at waterparks that used untreated mineral spring water (2,4 ).Compared with disinfected pools, these geothermal watersupplied pools pose an increased risk to swimmers because of their confined volume and lack of disinfection and filtration. Improved consumer education about the natural state of this water, guidelines to raise awareness about swimmer hygieneand health restrictions, and exploration of supplementary treatment might help prevent future outbreaks in these enclosed, untreated mineral-water pools.

The number of norovirus outbreaks increased from three during 1999–2000 to five during 2001–2002 ( 2). Thisincrease might be attributable to improvements in the awareness, availability, and use of laboratory detection methods for norovirus over previous years. During 2001–2002, tests for norovirus and other possible agents of viral origin appeared to be more routinely performed and documented in the outbreaks that were reported to CDC compared with previous reporting periods. A viral etiology was suspected in certain outbreaks of acute gastrointestinal illness of unknown etiology. Viral outbreaks are still likely to be underreported because improved technology for detection of viruses in stool and water samples is still not widely practiced. Investigators are encouraged to submit clinical specimens to CDC or state laboratories that conduct these tests. Guidelines for collectingstool specimens for identification of viral pathogens are available from CDC (23 ). Investigators are also encouraged to contact CDC and EPA regarding testing of water samples.


## Outbreaks Involving Dermatitis

This summary describes 21 outbreaks of dermatitis, continuing the increase in reported outbreaks documented in the previous two summaries (1997–1998: eight outbreaks [3 ]; 1999–2000: 15 outbreaks [ 2

]). Of the 21 dermatitis outbreaks, 20 (95.2%) were associated with spa or pool use, and 18 were thought to result from P. aeruginosa infections. In addition toskin infections, spas have also been associated with ear infections ( Pseudomonas), Pontiac fever/acute respiratory illness ( Legionella), and a previously unreported outbreak of Mycobacterium aviumcomplex/M. fortuitum( 15 ). The majority of these reports noted inadequate disinfection of the water ordeficient maintenance. Because the higher temperatures commonly used in spas deplete disinfectant levels at a more rapidrate, greater vigilance is required to maintain optimal spa waterquality parameters. Analysis of data from 5,209 spa inspections indicated that 2,958 (56.8%) identified >1 violation, and 11% of spa inspections resulted in immediate closure (24 ). This finding highlights the need for spa operators to actively check and maintain adequate disinfectant levels and other maintenance parameters. Strict adherence to maintaining optimal spa water quality (free chlorine: 3–5 ppm; pH: 7.2– 7.8) should prevent the majority of such outbreaks (25 ). Eight reported outbreaks of spa-associated rashes occurred among persons attending events (youth sports tournamentsor birthday parties) who were exposed at hotel facilities during the events. These outbreaks might have been detected because the close relationship among event participants allowed discussion of shared illness and facilitated reporting. However, outbreak reports also cited inadequate disinfection, bather overload, and improper hygiene (no showering after activities and before water entry) as contributing factors to these outbreaks. Combining inadequate maintenance withsubstantial numbers of users who can easily overload the disinfection capacity of the spa water might facilitate bacterial amplification and the spread of disease. As a result, spa and pool operators should consider enhancing maintenance levels,**Vol. 53 / SS-8 Surveillance Summaries 13**



### making water-quality checks more frequently, enhancing health education, and enforcing bather loads, particularly during heavy bather use (e.g., large sports tournaments or other events).

One presumed outbreak of cercarial dermatitis occurred among persons who swam in a freshwater lake. This syndromeis caused by an allergic response after penetration of the epidermis by avian larval schistosomes. Although the extent of the problem of cercarial dermatitis caused by freshwater exposure is unknown, it probably occurs more frequently than is reported to the WBDO surveillance system. Schistosomes occur naturally in ecosystems in which snails, birds, or aquatic mammals coexist, and a substantial number of freshwater lakes in the United States are therefore potential sources of illness among swimmers. To prevent further illnesses, swimmersshould pay careful attention to where they swim, avoid shallow swimming areas known to be snail habitats in lakes associated with cercarial dermatitis (particularly areas with onshorewinds), and report any incidents to their local health department (26 ).


## Outbreaks Involving PAM

The eight deaths associated with PAM reported during 2001–2002 were all linked to freshwater exposure. Typically, these infections are associated with swimming in freshwater bodies in the late summer months because the free-living ameba N. fowleri is thermophilic (i.e., it proliferates in warmer waters). The amebae are believed to enter through the nasal passage and then travel to the olfactory lobe of the brain. The mortality associated with infection by N. fowleri , particularly among young children, indicate that greater resources shouldbe devoted to educating the public and investigating the efficacy of potential prevention measures. To reduce risk, swimmers might wish to avoid swimming in freshwater venues when water temperatures are high and water levels are low, and should minimize forceful entry of water up the nasal passages during jumping or diving activities (i.e., by holding one’s nose or wearing nose plugs) and avoid digging in the sediment while under water ( 11 ).



## Outbreaks Associated with Chemical Exposure

Four outbreaks resulted from chemical exposures in treated aquatics venues resulting in acute respiratory symptoms. Two were a result of release of chlorine gas (used for disinfection) subsequent to improper maintenance and handling. The extreme health effects that might be caused by exposure to chlorine gas underscore the need for better training of pool operators who deal with gaseous chlorine as part of their daily activities. Two other outbreaks appeared to be related to accumulation of chloramines, a class of pool disinfection chemical byproducts or irritants ( 12–14 ), in the water and air surrounding indoor pools. These outbreaks illustrate that optimal indoor air quality at pools is critical to a safe and healthy swimming experience ( 12–14 ). More data are neededon indoor pool air quality so air-handling systems can be better designed to rid these venues of contaminating chloramines. Pool operators should be made aware that ventilation ofthese disinfection byproducts is key to avoiding future outbreaks and that effective pool management and education of swimmers about safe hygiene practices (e.g., showering before swimming and refraining from urinating in the pool) will minimize chloramine formation.

The mechanism for reporting chemical outbreaks is not as straightforward as it is for infectious disease outbreaks.Because communicable disease specialists are in different sections of health departments or in different agencies from environmental health or emergency response personnel, theymight not learn about acute recreational water-related chemical exposures. As a result, water-related chemical outbreaks are more likely than infectious disease outbreaks to be underreported. Closer communication and cross-training between these groups to recognize and investigate outbreaks might serve to improve future detection and reporting.



## Prevention

Prevention and control of recreational water-associated outbreaks requires a multifaceted approach. This approach should combine appropriate public health practices, environmental remediation, improved beach/pool maintenance and staff training, and enhanced education of the swimming publicabout infectious disease transmission at aquatic venues combined with simple, implementable protection measures.



## Conclusion
Data collected as part of the national WBDO surveillance system are used to describe the epidemiology of waterborne diseases in the United States. Identification of the etiologic agents and deficiencies responsible for these outbreaks is alsocritical because new trends might necessitate different interventions and changes in policies and resource allotment.

Surveillance for waterborne agents and outbreaks occurs primarily at the local and state level. Local and state publichealth authorities should be able to detect and recognize recreational water-associated outbreaks and implement appropriate prevention and control measures. Improved communication among local and state public health**14 MMWR October 22, 2004**



### departments, regulatory agencies, recreational water facilities,and the public would aid the detection and control of outbreaks. Routine reporting or sharing of inspection data between environmental health, infectious disease, and surveillance staff located within one or more agencies at thelocal or state level and with agencies in neighboring jurisdictions is recommended.

When an outbreak occurs, the timely collection of clinical specimens and water samples for testing and commencement of an environmental investigation might lead to more rapiddetection of the etiologic agent and the source of water contamination. However, the course of an investigation reflectsthe ability and capacity of public health departments and laboratories to recognize and investigate potential outbreaks of illness. Even when personnel are available to investigate a potential outbreak in a timely manner, investigations cannotalways be completed thoroughly. WBDO investigations typically require input from persons trained in different disciplines,including infectious disease epidemiology, environmental epidemiology, clinical medicine, sanitation, water engineering, and microbiology. Either further cross-training of existing personnel needs to be implemented, or additional personnel and resources need to made available or linked to those who typically investigate reports of WBDOs.

State health departments can request epidemiologic assistance and laboratory testing from CDC to investigateWBDOs. CDC and EPA can be consulted regarding engineering and environmental aspects of recreational water treatment and collection of large-volume water samples to identifypathogenic viruses, bacteria, and parasites, which require special protocols for their recovery. Requests for tests for viral organisms should be made to CDC’s Viral Gastroenteritis Section, Respiratory and Enterovirus Branch, Division of Viral and Rickettsial Diseases, National Center for InfectiousDiseases (NCID), at 404-639-3577. Requests for information or testing for Legionellashould be made to CDC’s Respiratory Diseases Branch, Division of Bacterial and Mycotic Diseases, at 404-639-2215. Requests for tests for parasites should be made to CDC’s Division of Parasitic Diseases, NCID, at 770-488-7756.

Additional information is available from • CDC’s Healthy Swimming website at http://

www.healthyswimming.org, which includes recreational water health communication and education materials for the general public and pool maintenance staff (e.g., information regarding disinfection, guidelines on response to fecal accidents [27], and fact sheets concerning recreational water illnesses); technical information regarding laboratory diagnostics; and an outbreak investigation toolkit that can be used by public health professionals; • EPA’s Beach website at http://www.epa.gov/OST/beaches; • CDC’s Voice and Fax Information System, 888-232-3228

(voice) or 888-232-3299 (fax) (choose cryptosporidiosis in the disease category); and• for reporting WBDOs, CDC’s Division of Parasitic Diseases, NCID, at 770-488-7756 or FAX at 770-488-7761; an electronic version of CDC’s reporting form (CDC 52.12, rev. 01/2003) is available at http://www.cdc.gov/ healthyswimming/downloads/cdc_5212_waterborne.pdf.

Acknowledgments The authors thank the following persons for their contributions to this report: state waterborne-disease surveillance coordinators; state epidemiologists; Robert Tauxe, M.D., Matt Moore, M.D., M.P.H., Barry Fields, Ph.D., Eric Mintz, M.D., M.P.H., Rachel Woodruff, M.P.H., Division of Bacterial and Mycotic Diseases, NCID, CDC; Marc-Alain Widdowson, M.A., Vet.M.B., M.Sc., Division of Viral and Rickettsial Diseases, NCID, CDC; Matthew Arduino, Dr.P.H., Joe Carpenter, Division of Healthcare Quality and Promotion, NCID, CDC; Mark Eberhard, Ph.D., James Maguire, M.D., Adria Prosser, Ph.D., Jacquelin Roberts, M.P.H., Division of Parasitic Diseases, NCID, CDC; Lorraine Backer, Ph.D., Mark McClanahan, Ph.D, Division of Environmental Hazards and Health Effects, NCEH, CDC.

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# Appendix Selected Case Descriptions of Outbreaks Associated with Recreational Wate r

**State in which Suspected Number**  **Outbreak outbreak or confirmed of persons date(s) occurred etiologic agent affected Case description** 

**Parasites**
July 2001

August 2001

July 2002

July 2002

July 2002

July 2002

August 2002 Illinois

Wyoming

Massachusetts

Minnesota

Georgia

Wyoming

Georgia Cryptosporidium hominis

Cryptosporidium species

Cryptosporidium species

Cryptosporidium species

Cryptosporidium species

Giardia intestinalis

Naegleria fowleri 358

2

767

52

3

2

1 A waterpark was implicated in the outbreak. Cryptosporidium was laboratory-confirmed in stool samples and the pool water. A fecal accident by a park visitor was the likely source of contamination. Waterpark records indicate that one fecal or vomit accident every 1–2 days was usual, and a subsequent investigation revealed that on the day most strongly associated with case illness, a fecal accident had occurred. Clean-up procedures in place (closing the pool for 20–30 minutes, removing organic material, and checking free-chlorine levels) were adequate for formed stool but not for liquid feces or Cryptosporidium inactivation ( **Source:** CDC. Responding to fecal accidents in disinfected swimming venues. MMWR 2001;50:416–7). The use of a common water circulation and filtration system for multiple pools might have contributed to cross-contamination and a larger number of cases. Hyperchlorination of the waterpark pool water apparently halted the outbreak.

A recreational facility with multiple flow-through pools using untreated hot spring water was the source of exposure. The pools were fed by hot springs via cooling ponds and the pools were drained and cleaned once a week. No chlorination or filtration requirements were in place for the water from the hot spring.

A full-service sports club was the source of infection. Routine inspections had revealed no major problems with the newly constructed outdoor pool area. The epicenter of the outbreak appears to have been the slide pool, but because all the pools in the children’s pool complex were serviced by a single filtration system, making a final determination was difficult. Epidemiologic evidence indicated that infection from the pool was ongoing all summer, but that transmission peaked in mid-August during a massive heat wave.

Illness was associated with a health club indoor swimming pool inwhich schoolchildren were taking swimming lessons. An investigation revealed that in the 2 weeks before the outbreak, the chlorine feeder had been out of service, and the chlorine had been administered by hand. The flow meters had not been working, and the rate-of-flow meter readings were not monitored or documented. The filter sand bed was later discovered to be missing 8 of the required 18 vertical inches of sand. After the outbreak, the recirculation pump, filter, and flow-meter were replaced with pool code-compliant models.

Children at a child care center became ill after a reported fecal accident in a wading pool for young children. Records on water treatment for the pool were not available.

A river that was used by local residents for swimming, surfing (with river boards), and kayaking was the implicated site. It was in an undeveloped area, access to the site was completely open, and the possibility of human or animal contamination was high.

A previously healthy boy aged 11 years received a diagnosis of primary amebic meningoencephalitis after hospital admission with symptoms of headache, seizures, and vomiting. He later died. Hehad swum in a local river 9 days earlier. Environmental investigation revealed a high river temperature (91.4 o F [33 o C]) and low water level; and N. fowleri was isolated from river water samples ( **Source:** CDC. Primary amebic meningoencephalitis—Georgia, 2002. MMWR 2003;52:962).**Vol. 53 / SS-8 Surveillance Summaries 17**

**Bacteria State**  **in which Suspected Number Outbreak outbreak or confirmed of persons**  **date(s) occurred etiologic agent affected Case description**

August 2002

August 2002

July 2001

July 2001

July 2001

March 2002

March 2002

July 2002 Texas

Minnesota

Minnesota

South Carolina

Minnesota

Wisconsin

Minnesota

Wisconsin C. hominis

Cryptosporidium species

Escherichia coli O157:H7

E. coli O157:H7

Norovirus

Norovirus

Norovirus

Norovirus, Cryptosporidium species, Shigella sonnei 54

16

20

45

40

15

36

44 The common exposure for those who became ill was a wading pool at a resort hotel. Investigators believe that use of the wading pool by diaper-aged children led to its contamination.

An all-inclusive lakeside resort with adult and children’s swimming pools was the site of the outbreak. Initial inspection of the pool documented zero free chlorine in the water, and pool water-quality records for this time ranged from incomplete to nonexistent. Adirect connection between the well water system and the swimming pool, and a recirculation rate that was <50% of the required rate probably contributed to the outbreak. The pools and spa were closed for the remainder of the season.

A lake beach located in a metropolitan area was the outbreak source. Environmental investigation identified high fecal coliform levels but did not detect any failed sewage systems in lake homes that might have contributed. The beach was closed for the rest of the season; ongoing monitoring indicated that the fecal coliform levels did not decrease for the rest of the summer. City officials believed that the high number of geese that occupied the beach during the summer might have contributed to the elevated overall fecal coliform levels.

A swimming beach at a state park was the site of the outbreak. Fecal contamination directly at the beach or of the stream that fed the lake was suspected. Lake water exceeded guidelines for fecal coliforms in subsequent testing.

The outbreak was associated with use of a freshwater lake beach. Forty persons became ill, and 27 secondary cases were identified. The beach was frequented by diaper-aged children but lacked any hand-washing facilities. Two incidents of a child vomiting on the beach were reported. Epidemiologic evidence indicates that this waterborne outbreak might have been part of a larger norovirus outbreak occurring in the community during that time.

Fifteen of 19 persons from four related families became ill after swimming in a hotel pool. The most commonly reported symptoms were vomiting (87%) and diarrhea (80%).

Team members of three youth sports teams and family members became ill after staying at a hotel. The most common symptoms were vomiting (81%), diarrhea (56%), cramps (53%), and fever (44%). The environmental health assessment and epidemiologic evidence implicated the hotel pool as the source of the infection.

Persons became ill after swimming at a state park beach locatedon one of the Great Lakes. The most frequently reported symptoms were vomiting (75%), diarrhea (66%), and fatigue (34%). Additionally, 22 secondary cases were identified. Environmental investigation revealed high E. coli levels on multiple occasions after the outbreak. Contamination might have resulted from bathers or dumping of sewage from boats moored offshore. Of the 44 persons with primary cases, 21 (49%) admitted to beach use and swimming after their onset of illness. After the investigation, beach-closure policies were changed, and the beach was subsequently closed to swimming five times, in each instance <48 hours after a rainfall event. This is the first documented disease outbreak associated with the Great Lakes since reporting began in 1978. **Viruses 18 MMWR October 22, 2004** 

**State in which Suspected Number**  **Outbreak outbreak or confirmed of persons date(s) occurred etiologic agent affected Case description** 

September 2001

June 2002

September 2002

October 2002

March 2001

May 2001

May 2001 Wisconsin

Ohio

Alaska

West Virginia

Florida

Pennsylvania

Pennsylvania Chloramines

Chlorine gas

Chlorine gas

Chloramines

Pseudomonas aeruginosa

P. aeruginosa

P. aeruginosa 20

20

30

32

53

42

2 Members of a school swim team reported symptoms after swimming at the school’s indoor pool. The most commonly reported symptoms were hair loss (95%), skin rash (85%), and breathing difficulties (60%). The automatic chlorine monitoring system had been malfunctioning, and the chlorine feeder was operated manually. This might have caused high levels of chlorine to be fed into the pool, leading to an accumulation of chloramines. Breathing difficulties were likely caused by exposure to the water and air after accumulation of chloramines at the indoor pool.

Eleven persons were taken to the hospital with nausea and respiratory symptoms after a release of chlorine gas at a waterpark. Two boys aged 12 years were admitted; the others were released. Repairs had recently been made to the waterlines feeding the pool. The chlorine disinfection feed system was probably not shut down when the water flow stopped during repair, resulting in chlorine gas release.

A maintenance worker and young swimmers experienced severe respiratory symptoms at a campus pool after the maintenance worker mistakenly mixed chlorine and hydrochloric acid. Of 30 persons who were taken to area hospitals, 15 were hospitalized. The worker was refilling the hypochlorite drum and mistakenly refilled with acid that was in a similarly colored drum. A lack of sufficient and appropriate pool operator training and failure to verify the contents of chemical containers were implicated as contributing causes of this incident.

Persons staying at a hotel who were exposed to indoor pool air and water became ill. The most common symptoms were cough (84%), eye irritation (78%), throat irritation (66%), and difficulty breathing (41%). The proportion of exposed persons who became ill increased with increased duration of exposure to air around theswimming pool and swimming pool water. Water quality parameters did not meet state standards, with pH >8.5 and combined chlorine >0.7 ppm.

Infections involved team members who stayed at a hotel and used the spa. Inspection determined that the water was turbid and contained high bacterial levels, including Pseudomonas. Contributing factors to this outbreak were inadequate chlorination and bather overload.

Participants in a youth sports tournament experienced folliculitis after using a hotel spa that was subsequently identified as having a high bacterial count. Contributing factors to this outbreak were failure to shower before spa use, not adhering to the bather load limit, and inadequate spa maintenance. The following two outbreaks involved participants in the same tournament who stayed at different hotels. In addition to the 64 cases identified by these three reports, >150 persons associated with this tournament became ill.

Participants in a youth sports tournament experienced folliculitis after using a hotel spa. The contributing factors were the same as those in the other May 2001 Pennsylvania outbreak involving P. aeruginosa . Investigators were not able to determine the scope of the outbreak as those affected lived out of state and did not cooperate with the investigation. **Chemicals**

**Other Vol. 53 / SS-8 Surveillance Summaries 19** 

**State in which Suspected Number**  **Outbreak outbreak or confirmed of persons date(s) occurred etiologic agent affected Case description** 

May 2001

May 2001

February 2002

February 2002

March 2002

November 2002 Pennsylvania

Minnesota

Alaska

Ohio

Ohio

Maine Bacillus species

P. aeruginosa

P. aeruginosa

P. aeruginosa

P. aeruginosa

Acute gastrointestinal illness of unknown etiology 20

6

110

18

31

33 **Unknown** Participants in a youth sports tournament developed folliculitis after using a hotel spa. The contributing factors were the same as those associated with the other two May 2001 Pennsylvania outbreaks.

An in-room spa (a noncommercial model) at a resort was implicated in this outbreak of folliculitis. Five persons (83.3%) also reported a sore throat. P. aeruginosa was cultured from both skin and spa water.

Persons experienced folliculitis after their hotel stay and use of the pool or spa. P. aeruginosa was isolated from skin swabs as well as pool and spa water. Examination of chlorination records revealed that the free-chlorine levels for both the pool and spa were outside the acceptable range 75% of the time. Employees lacked required training and certification.

Fifteen females experienced folliculitis after staying at a hotel during a sports competition. They all reported use of the spa. Upon inspection, the spa was determined to have no residual chlorine; the pH was 8.0, and the autocontroller for disinfection was turned off. Environmental samples taken from the spa and pool tested positive for P. aeruginosa. Three other hotel guests also became ill.

Persons attending a birthday pool party initially reported rashes after their visit, and other ill hotel guests were identified. The pool alarm was sounding at the time of the original inspection. No certified pool operator was employed. A remote monitoring service was engaged to oversee chlorination. Inspection revealed that the connections from the controller were reversed for acid and chlorine feed.

Children were playing in a puddle during recess. The puddle was a result of excess rains and an overflowing septic tank and had high levels of E. coli. Children were believed not to have washed their hands after playing in the puddle and before eating lunch.**20 MMWR October 22, 2004** 

# Glossary

cercarial dermatitis Dermatitis caused by contact/skin perforation by the cercariae (larval stage) of certain species of schistosomes (parasites) whose normal hosts are birds and nonhuman mammals. This allergic response does not lead to parasitic infestation in humans and produces no long-term disease.

class Waterborne-disease outbreaks are classified according to the strength of the epidemiologic and water-quality data implicating water as the source of the outbreak (see Table 1).

chloramines Disinfection by-products form when free chlorine combines with nitrogen-containing compounds (e.g., urine or perspiration). They can cause eye, skin, lung, and throat irritations and have low disinfection capability. They accumulate in water and the air over pools.

coliforms All aerobic and facultative anaerobic, gram-negative, nonspore-forming, rod-shaped bacteria that ferment lactose with gas formation within 48 hours at 95 o 

### F (35 o 

### C).

combined chlorine level See chloramines. The level of chlorine that has combined with organic compounds in the water and is no longer an effective disinfectant.

contact time The length of time water is exposed to a disinfectant; usually measured in minutes (e.g., chlorine contact time).

Cryptosporidium hominis The taxonomy of Cryptosporidium has evolved as a result of advancements in molecular methodology and genotyping. The former C. parvumnow refers to a species that is zoonotic and infects ruminants and humans. C. hominis refers to the species of Cryptosporidium that is infective only in humans and monkeys. Both species were referred to previously as C. parvum

. disinfection by-products Chemicals formed in water through reactions between organic matter and disinfectants. Includes chloramine, an irritant of the eyes, nose, and throat.

fecal coliforms Coliforms that grow and produce gas at 112.1 o 

### F (44.5 o 

### C) within 24 hours.

filtration The process of removing suspended particles from water by passing it through one or more permeable membranes or media of limited 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, residual chlorine level The concentration of chlorine in water that is not combined with other constituents, thus serving as an effective disinfectant.

freshwater 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 intended for (or accessible to) recreational use. 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.**Vol. 53 / SS-8 Surveillance Summaries 21**



### marine water Untreated recreational water at an ocean setting.

norovirus A group of related, single-stranded RNA, nonenveloped viruses (genus Norovirus, family Caliciviridae ) that cause acute gastroenteritis in humans. Norovirus was recently approved as the official genus name for the group of viruses provisionally described as Norwalk-like viruses (NLV).

oocyst The infectious stage of Cryptosporidium species and certain other coccidian parasites with aprotective wall that facilitates survival in water and other environments and renders the parasite extremely resistant to chlorine.

recreational water venue A body of water used for the purpose of recreation (e.g., swimming, soaking, and athletics)including any structure that encloses this water. Can include lakes, rivers, the ocean, and manmade venues (e.g., swimming pools, spas, and waterparks).

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 use 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. Sometimes referred to as a hot tubor whirlpool

.

treated water Water that has undergone a disinfection process (e.g., chlorination, filtration) for the purpose of making it safe for recreation. This usually refers to any recreational water in an enclosed, manufactured structure but might include swimming or wading pools, fountains, or spas filled with untreated or treated tap water that receives no further treatment.

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. Thebest indicator is one whose density or concentration correlates best with health hazards associated with a type of hazard or pollution.**22 MMWR October 22, 2004 Vol. 53 / SS-8 Surveillance Summaries 23** 



# Surveillance for Waterborne-Disease Outbreaks Associated with Drinking Water — United States, 2001–2002

Brian G. Blackburn, M.D., 1,2 Gunther F. Craun, M.P.H., 3 Jonathan S. Yoder, M.P.H., M.S.W., 1,4 Vincent Hill, Ph.D., 1 Rebecca L. Calderon, Ph.D., 5 Nora Chen, Sc.M., 4 Sherline H. Lee, M.P.H., 6 Deborah A. Levy, Ph.D., 6 Michael J. Beach, Ph.D. 1
1 Division of Parasitic Diseases, National Center for Infectious Diseases, CDC; 2 Epidemic Intelligence Service, Epidemiology Program Office, CDC ; 3 Gunther F. Craun and Associates Staunton, Virginia; 4 Public Health Prevention Service, Epidemiology Program Office, CDC; 5 U.S. Environmental Protection Agency, Research Triangle Park, North Carolina; 6 Division of Healthcare Quality Promotion, National Center for Infectious Diseases, CDC 

### Abstract

Problem/Condition: Since 1971, CDC, the U.S. Environmental Protection Agency, and the Council of State and Territorial Epidemiologists have maintained a collaborative surveillance system for collecting and periodically reporting data related to occurrences and causes of waterborne-disease outbreaks (WBDOs). This surveillance system is the primary source of data concerning the scope and effects of waterborne disease outbreaks on persons in the United States. Reporting Period Covered: This summary includes data on WBDOs associated with drinking water that occurred during January 2001–December 2002 and on three previously unreported outbreaks that occurred during 2000. Description of the System: Public health departments in the states, territories, localities, and the Freely Associated States are primarily responsible for detecting and investigating WBDOs and voluntarily reporting them to CDC on astandard form. The surveillance system includes data for outbreaks associated with both drinking water and recreational water; only outbreaks associated with drinking water are reported in this summary.
Results: During 2001–2002, a total of 31 WBDOs associated with drinking water were reported by 19 states. These 31 outbreaks caused illness among an estimated 1,020 persons and were linked to seven deaths. The microbe or chemical that caused the outbreak was identified for 24 (77.4%) of the 31 outbreaks. Of the 24 identified outbreaks, 19 (79.2%) were associated with pathogens, and five (20.8%) were associated with acute chemical poisonings. Five outbreaks were caused by norovirus, five by parasites, and three by non- Legionellabacteria. All seven outbreaks involving acute gastrointestinal illness of unknown etiology were suspected of having an infectious cause. For the first time, this MMWR Surveillance Summary includes drinking water-associated outbreaks of Legionnaires disease (LD); six outbreaks of LD occurred during 2001–2002. Of the 25 non- Legionella associated outbreaks, 23 (92.0%) were reported in systems that used groundwater sources; nine (39.1%) of these 23 groundwater outbreaks were associated with private noncommunity wells that were not regulated by EPA. Interpretation: The number of drinking water-associated outbreaks decreased from 39 during 1999–2000 to 31 during 2001–2002. Two (8.0%) outbreaks associated with surface water occurred during 2001–2002; neither was associated with consumption of untreated water. The number of outbreaks associated with groundwater sources decreased from 28 during 1999–2000 to 23 during 2001–2002; however, the proportion of such outbreaks increased from 73.7% to 92.0%. The number of outbreaks associated with untreated groundwater decreased from 17 (44.7%) during 1999–2000 to 10 (40.0%) during 2001–2002. Outbreaks associated with private, unregulated wells remained relatively stable, although more outbreaks involving private, treated wells were reported during 2001–2002. Because the only groundwater systems that are required to disinfect their water supplies are public systems under the influence of surface water, these findings support EPA’s development of a groundwater rule that specifies when corrective action (including disinfection) is required.
Public Health Action: CDC and EPA use surveillance data 1) to identify the types of water systems, their deficiencies, and the etiologic agents associated with outbreaks and 2) to evaluate the adequacy of technologies for providing safe drinking water. Surveillance data are used also to establish research priorities, which can lead to improved water-qualityregulations. CDC and EPA recently completed epidemiologic studies that assess the level of waterborne illness attributable to municipal drinking water in nonoutbreak conditions. The decrease in outbreaks in surface water systems isattributable primarily to implementation of provisions of EPA rules enacted since the late 1980s. Rules under development by EPA are expected to protect the public further from microbial contaminants while addressing risk tradeoffs of disinfection byproducts in drinking water. Corresponding author: Brian G. Blackburn, M.D., EIS Officer, CDC/ NCID/DPD, 1600 Clifton Rd., NE, MS F-22, Atlanta, GA 30341; Fax: 770-488-7761; E-mail: bblackburn@cdc.gov.**24 MMWR October 22, 2004**



## Introduction During 1920–1970, statistical data regarding U.S.waterborne-disease outbreaks (WBDOs) 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 maintained a collaborative surveillance system that tracks the occurrences and causes of WBDOs associated with drinking water; tabulation of recreational water-associated outbreaks was added to the surveillance system in 1978 (2–7). The surveillance system includes data regarding outbreaks associated with drinking water, recreational water, and other types of water exposures. This MMWR Surveillance Summary includes data for drinking water-associated outbreaks that occurredduring 2001–2002 and for three previously unreported outbreaks that occurred in 2000. Recreational water-associated outbreaks are presented in a separate MMWR Surveillance Summary ( 8). These surveillance activities are intended to 1) characterize the epidemiology of WBDOs; 2) identify changing trends in the etiologic agents that caused WBDOs and determine why the outbreaks occurred; 3) encourage public health personnel to detect and investigate WBDOs; and 4) foster collaborationamong local, state, federal, and international agencies on initiatives to prevent waterborne disease transmission. Dataobtained through this surveillance system are useful for identifying major deficiencies in providing safe drinking water. Surveillance information can influence research priorities andlead to improved water-quality regulations. However, the statistics reported in this surveillance summary represent only a portion of the burden of illness associated with drinking water exposure. The surveillance information does not include endemic waterborne disease risks, nor are reliable estimatesavailable of the number of unrecognized WBDOs and associated cases of illness.



## Background

EPA Drinking Water Regulations

Public water systems are regulated under the Safe Drinking Water Act (SDWA) of 1974 and its subsequent 1986 and 1996 amendments (Table 1) (9–11 ). SDWA authorizes EPA to set national standards to protect drinking water and its sources against naturally occurring or human-made contaminants. Microbial contamination is regulated under the Total Coliform Rule (TCR), Surface Water Treatment Rule (SWTR), Interim Enhanced SWTR (IESWTR), and Long Term 1 Enhanced SWTR (LT1ESWTR). In addition, EPA’s lead, copper, and arsenic rules prescribe action levels at which a system must take corrective steps ( 12,13 ). These rules have been described previously (2).

All public water systems are required by TCR to monitor for total coliforms at a prescribed frequency ( 14,15 ). SWTR ( 16 ) and IESWTR ( 17 ) apply to public systems that serve >10,000 persons and that use surface water or groundwater under the direct influence of surface water and are intended to protect the public against exposure to Giardia intestinalis

, Cryptosporidium , viruses, Legionella , and selected other pathogens. LT1ESWTR applies to public systems that serve <10,000 persons and is intended to improve the control of microbial pathogens, especially Cryptosporidium( 18,19 ). An additional regulation, the Filter Backwash Recycling Rule, requires the return of recycle flows to the water treatment process so microbial contaminant removal is not compromised ( 19,20 ). Recently proposed microbial and disinfection byproducts regulations include the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and the Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR). These regulations were developed simultaneously to address risk tradeoffsbetween control of pathogens and limiting exposure to disinfection byproducts (DBPs) that can form in water from the disinfection process used to control microbial pathogens (21 ).

LT2ESWTR (22,23) mandates source-water monitoring for Cryptosporidiumand additional treatment for filtered systems on the basis of source-water concentrations; inactivation of Cryptosporidiumby all unfiltered systems; disinfection profiling and benchmarking to ensure continued levels of microbial protection while system operators take steps to comply with new DBP limits; and covering, treating, or implementing **TABLE 1. Environmental Protection Agency regulations regarding drinking water, by year enacted — United States,**  **1974–2003 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 Groundwater Rule (proposed) 2000 Lead and Copper Rule — action levels 2000 Long Term 1 Enhanced SWTR 2002 Long Term 2 Enhanced SWTR 2003 Stage 2 D-DBP Rule 2003**Vol. 53 / SS-8 Surveillance Summaries 25**



### a risk-management plan for uncovered finished water-storage facilities.

DBPR applies to all community and nontransient, noncommunity water systems that add a disinfectant other than ultraviolet light (24). DBPR requires systems to meet maximum contaminant levels at each monitoring site in the distribution system, determine if they are experiencing short-term peaks in DBP levels, and better identify monitoring sites at which consumers are exposed to high DBP levels.

The 1996 amendments require EPA to develop regulationsthat mandate disinfection of groundwater systems as necessary to protect the public health. The proposed Ground Water Rule (GWR) (information available at http://www.epa.gov/safewater/gwr.html) will specify when corrective action, including disinfection, is required to protect consumers from bacteria and viruses (25 ). Proposed requirements include periodic sanitary surveys to identify deficiencies,hydrogeologic sensitivity assessments for undisinfected systems, source-water microbial monitoring from certain systems,and compliance monitoring for systems that disinfect to ensure adequate inactivation or removal of viruses. SDWA’s Wellhead Protection Program requires every state to develop a program to delineate wellhead protection areas in whichsources of contamination are managed to minimize groundwater contamination (25). Additional protection of groundwater sources, especially from contamination by shallow wells and cesspools, is provided by the Underground Injection Control Regulations (26 ).Every 5 years, EPA is also required to publish a list of contaminants that are known or anticipated to occur in public water systems and that might need to be regulated. The first drinking water Contaminant Candidate List (CCL) was issued in 1998 and included 50 chemical and 10 microbial contaminants (27 ); however, EPA decided not to regulate any of the waterborne pathogens included in CCL. EPA also mustestablish criteria for a program to monitor unregulated contaminants and publish a list of contaminants to be monitored (28–30). Microorganisms were included among the contaminants for which analytical methods are available ( Aeromonas) and contaminants for which analytical methods are being developed ( Helicobacter pylori, cyanobacteria, coxsackieviruses, microsporidia, adenoviruses, and caliciviruses). An ongoing screening survey for Aeromonas , and selected chemical contaminants will help determine whether these should be considered or excluded for regulation. 

## Methods

Data Sources

Public health departments in the states, territories, localities, and the Freely Associated States* (FAS) have primary responsibility for detecting and investigating WBDOs, which they report voluntarily to CDC by 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 the outbreak,including person, place, time, and location; results from epidemiologic studies conducted; specimen and water sample testing; and other factors potentially contributing to the outbreak (e.g., environmental concerns, disinfection, and filtration[Glossary]). CDC annually requests reports from state, territorial, and FAS epidemiologists or persons designated as WBDO surveillance coordinators and obtains additional information regarding water quality and treatment as needed. Numeric and text data are abstracted from the outbreak form and supporting documents and entered into a database for analysis.



## Definitions †



### The unit of analysis for the WBDO surveillance system is an outbreak, not an individual case of a waterborne disease.Two criteria must be met for an event to be defined as a drinking water-associated disease outbreak. First, >2 persons must have experienced a similar illness after exposure to water. This criterion is waived for single cases of laboratory-confirmed primary amebic meningoencephalitis (PAM) and for singlecases of chemical poisoning if water-quality data indicate contamination by the chemical. Second, epidemiologic evidence must implicate drinking water as the probable source of the illness. Reported outbreaks caused by contaminated water or ice at the point of use (e.g., a contaminated water faucet orserving container) are not classified as drinking waterassociated outbreaks, and WBDOs associated with cruise ships are not summarized in this report.

Different types of drinking water systems are used for outbreak classification (Figure 1). Public water systems, which are classified as either community or noncommunity systems (Glossary), are regulated under SDWA. Of the approximately 161,000 public water systems in the United States, 108,000

* 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. † Additional terms are defined in the Glossary.**26 MMWR October 22, 2004**



### (67.1%) are noncommunity systems, including 88,000 transient systems and 20,000 nontransient systems (Glossary), and53,000 (32.9%) are community systems. Despite representing a minority of water systems, community systems serve273 million persons (approximately 93.9% of the U.S. population) (31 ). Furthermore, a limited number of communitysystems (3,900 [7.4%]) provide water to 81% of the community system population ( 31 ). Noncommunity, nontransientsystems provide water to 6.3 million persons, and 23.3 million persons use noncommunity, transient systems (by definition, these populations also use another type of water systemat their residences, except for the limited number of permanent residents of nontransient systems) (31 ). Although the majority of public water systems (90.9%) are supplied bygroundwater, more persons (66.2%) drink from public systems served by surface water. Approximately 17 million persons (6.0%) rely on private, individual water systems (31 ) (Glossary).

In this surveillance system, drinking water-associated outbreaks involving water not intended for drinking (e.g., lakes, springs, and creeks used by campers and boaters; irrigation water, and other nonpotable sources with or without taps) are also classified as individual systems (Glossary). Sources used for bottled water are also classified as individual systems;bottled water is not regulated by EPA but is subject to regulation by the Food and Drug Administration (FDA). Each drinking water system associated with a WBDO is classified as having a deficiency. Deficiency classifications are as follows:

1: untreated surface water; 2: untreated groundwater; 3: treatment deficiency (e.g., temporary interruption of disinfection, chronically inadequate disinfection, or inadequate or no filtration); 4: distribution system deficiency (e.g., cross-connection, contamination of water mains during construction or repair, or contamination of a storage facility); and5: unknown or miscellaneous deficiency (e.g., contaminated bottled water or water source not intended for drinking, such as irrigation water).



## Outbreak Classification

WBDOs reported to the surveillance system are classified according to the strength of the evidence implicating water as the vehicle of transmission (Table 2). The classification scheme(i.e., Classes I–IV) is based on the epidemiologic and waterquality data provided on the outbreak report form. Epidemiologic data are weighted more than water-quality data. Although outbreaks without water-quality data might be included in this summary, reports that lack epidemiologic data were excluded. Single cases of PAM or chemical poisoning are Drinking water systems

Public water systems public or private ownership (subject to EPA* regulations) Individual water systems (might be subject to 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 (commercial bottled water

is regulated by FDA ; persons might also fill their own containers) †

§ **FIGURE 1. Types of drinking water systems used for outbreak classification**

* Environmental Protection Agency. † Food and Drug Administration. § In certain instances, bottled water is used in lieu of a community supply or by noncommunity systems.**Vol. 53 / SS-8 Surveillance Summaries 27**



### not classified according to this scheme. Weighting of epidemiologic data does not preclude the relative importance of both types of data. The purpose of the outbreak system is not only to implicate water as the vehicle for the outbreak but also to understand the circumstances and system breakdowns that led to the outbreak.

A classification of I indicates that adequate epidemiologic and water-quality data were reported (Table 2). However, the classification does not necessarily imply that an investigation was conducted optimally, nor does a classification of II, III,or IV imply that an investigation was inadequate or incomplete. Outbreaks and the resulting investigations occur under different circumstances, and not all outbreaks can or should be rigorously investigated. In addition, outbreaks that affect fewer persons are more likely to receive a classification of IIIrather than I because of the relatively limited sample size available for analysis.

For the reporting period 2001–2002, WBDOs associated with drinking water and with recreational water are reported separately for the first time. The MMWR Surveillance Summary of recreational water-associated outbreaks ( 8) includesWBDOs related to recreational water as defined in the methods section of that summary. This MMWR Surveillance Summary includes waterborne outbreaks related to drinking water, those occurring in occupational settings, those associated with Legionella species, and other miscellaneous outbreaks. Although outbreaks of Pontiac fever have been included in previous MMWR Surveillance Summaries of WBDOs, thissummary is the first to include outbreaks of Legionnaires disease (LD). Because nearly all outbreaks attributed to Legionella species share characteristics that are distinct from other types of WBDOs, all Legionella outbreaks have been compiled into a single table in this report that identifies the primary use of the water implicated in the outbreak. Although all Legionella outbreaks are listed in this table, only those that occurred in association with water primarily intended for drinking or occupational use are discussed in this summary. Outbreaks of LD that occurred in association with water intended primarilyfor recreational use are discussed in the summary of recreational water-associated outbreaks ( 8).

Because the parameters used in this summary to assess drinking water-associated outbreaks (i.e., water system type, water source, and deficiency) do not permit adequate evaluation of the characteristics associated with Legionella outbreaks, such parameters are not applied to Legionella outbreaks. For this

reason, Legionella outbreaks are counted not in tables and statistics that include these parameters, but only in those related to the total number of drinking water outbreaks and the etiologic agent of these outbreaks.



## Results During 2001–2002, a total of 31 outbreaks (19 during 2001 and 12 during 2002) associated with drinking water were reported by 19 states (Figure 2) compared with 39 outbreaksduring 1999–2000 (Figures 3 and 4). (Selected case descriptions are located in the Appendix). These 31 outbreaks caused illness among an estimated 1,020 persons, resulting in 51 hospitalizations and seven deaths. The median number ofpersons affected in an outbreak was six (range: 2–230). Outbreaks peaked during June–September (Figure 5). Florida reported the most outbreaks (eight) during this reporting period.

On the basis of epidemiologic and water-quality data, nine (29.0%) of the 31 outbreaks were assigned to Class I, two (6.5%) to Class II, 19 (61.3%) to Class III, and one (3.2%) to Class IV. Outbreaks were analyzed by state (Tables 3, 4, and 5) and tabulated by etiologic agent and water system type (Table 6), type of deficiency and water system (Table 7), and type of deficiency and water source (Table 8). Outbreaks attributable to Legionella are excluded from the analysis of outbreaks by etiologic agent, water system, amd type of deficiency. **TABLE 2. Classification of investigations of waterborne-disease outbreaks — United States Class Epidemiologic data Water-quality data**  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 Historical information or laboratory data (e.g., the history that a chlorinator malfunctioned or a water main broke, no detectable free-chlorine residual, or the presence of coliforms in the water)

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

Provided and adequate

Not provided or inadequate I

II

III

IV**28 MMWR October 22, 2004**



## Etiologic Agents

Of the 31 outbreaks, 19 (61.3%) were of known infectious etiology, seven (22.6%) were of unknown etiology, and five (16.1%) were attributed to chemical poisoning. The outbreaks of known infectious etiology included six (19.4%) that were caused by Legionellaspecies, five (16.1%) by viruses, five (16.1%) by parasites, and three (9.7%) by bacteria other than Legionella species (Figure 6). Unidentified Etiologic Agents Seven outbreaks affecting 117 persons were reported that involved acute gastrointestinal illness of unknown etiology(AGI); no hospitalizations or deaths resulted from these illnesses. Stool specimen testing to identify a causative agent was attempted in only one of these outbreaks. In another ofthese outbreaks, norovirus was suspected on the basis of symptoms and incubation period in an outbreak of gastrointestinalillness at a church camp in Pennsylvania. However, no confirmatory testing was done of patient samples or of the implicated water. No suspected etiologic agent was noted for any of the other outbreaks in this category. Legionella Species

Six outbreaks were attributed to Legionella species. These are described on page 33 of this report.

Viruses

Five outbreaks affecting 727 persons were attributed to viral infections, all attributed to norovirus. Of the six outbreaks affecting the most persons reported in this summary, five werecaused by norovirus. Illnesses from these five outbreaks resulted in two hospitalizations and one death.

Parasites

Five outbreaks affecting 30 persons were attributed to parasitic infection: three Giardia intestinalisoutbreaks, one Cryptosporidiumoutbreak, and one Naegleria fowleri outbreak. Illnesses from these outbreaks resulted in five hospitalizations and two deaths; both deaths were caused by N. fowleri infection.

Chemicals Five outbreaks affecting 39 personswere attributed to chemical contamination. Two were caused by high levels ofcopper and a third by high levels of copper and other metals. One outbreak was caused by ethylene glycol contamination of a school’s water supply and one byethyl benzene, toluene, and xylene contamination of bottled water. Illnesses from these five outbreaks resulted in no hospitalizations or deaths. Bacteria (Other Than Legionella Species)

Three outbreaks affecting 27 persons were attributed to bacterial infection (other than Legionella species): one Escherichia coli O157: H7 outbreak, one 0 10 20 30 40 50 60

1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001
Year Legionella species* AGI † Chemical Viral Parasitic Bacterial Number of outbreaks **FIGURE 3. Number of waterborne-disease outbreaks (n = 764) associated with drinking water, by year and etiologic agent — United States, 1971–2002** 

* Beginning in 2001, Legionnaires disease was added to the surveillance system, and Legionella species were classified separately. † Acute gastrointestinal illness of unknown etiology. No. of oubreaks No. of states

>4 1

3 1

2 3

1 14

0 31 **FIGURE 2. Number of waterborne-disease outbreaks*** **(n = 31) associated with drinking water, by state — United States, 2001–2002** 

* Numbers are dependent on reporting and surveillance activities in

individual states and do not necessarily indicate that more outbreaks occur in a given state.**Vol. 53 / SS-8 Surveillance Summaries 29**

**TABLE 3. Waterborne-disease outbreaks (n = 17) associated with drinking water — United States, 2001**
**No. of Predominant cases Type of**  **State Month Class Etiologic agent illness (n = 508) system* Deficiency** **† Source Setting** 

Alaska Jun I Campylobacter jejuni and Yersinia enterocolitica § Gastroenteritis 12 Ncom 2 Well Bunkhouse Colorado Feb III Giardia intestinalis Gastroenteritis 6 Com 3 River/stream Community Florida Apr III AGI ¶ Gastroenteritis 3 Ind 3 Well Household Florida Apr III AGI Gastroenteritis 4 Ind 3 Well Household Florida Apr III G. intestinalis Gastroenteritis 6 Ind 2 Well Household Florida Jul III AGI Gastroenteritis 4 Ind 3 Well Household Florida Aug III Ethylene glycol Gastroenteritis 3 Com 4 Well School Florida Sep III Ethyl benzene, toluene, xylene Gastroenteritis 2 Ind 5 Spring (bottled) Bottled water Illinois Oct II AGI Gastroenteritis 79 Ncom 5 Well School Indiana Aug IV Cryptosporidium species Gastroenteritis 10 Ind 3** Well Household Minnesota Sep III Copper and other minerals Gastroenteritis 4 Ncom 4 Well Church Minnesota Nov III Copper Gastroenteritis 28 Com 4 Well School Ohio Sep III Copper Gastroenteritis 2 Com 4 River/stream Steel plant Pennsylvania Jun II AGI Gastroenteritis 19 Ncom 3 Well Camp Wisconsin Jan I C. jejuni Gastroenteritis 13 Ind 2 Well Household Wyoming Jan I Norovirus Gastroenteritis 230 Ncom 2 Well Lodge Wyoming Sep I Norovirus Gastroenteritis 83 Ncom 3 Well Restaurant
* Com = community; Ncom = noncommunity; Ind = individual. Community and noncommunity water systems are public water systems thatserve >15 service

connections or 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 with >15 service connections or an average of >25 residents. A noncommunity water system 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 or schools), whereas transient systems pr ovide water to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individ ual water systems are small systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with water notintended for drinking (e.g., lakes, springs and creeks used by campers and boaters, irrigation water, and other nonpotable sources with or without taps) are also classified as individual systems. † 1 = untreated surface water; 2 = untreated groundwater; 3 = treatment deficiency (e.g., temporary interruption of disinfection, chronically inadequate

disinfection, and inadequate or no filtration); 4 = distribution system deficiency (e.g., cross-connection, contamination of wa ter mains during construction or repair, and contamination of a storage facility); and 5 = unknown or miscellaneous deficiency (e.g., contaminated bottled wateror storage container). § Six persons had stool specimens that tested positive for C. jejuni , and one person had stool specimens that tested positive for Y. enterocolitica. ¶ Acute gastrointestinal illness of unknown etiology. ** Intentional bypass of a reverse osmosis filter occurred. Historically, filter bypass has been classified as treatment deficie ncy rather than as untreated water. **FIGURE 5. Number of waterborne-disease outbreaks (n = 31) associated with drinking water, by etiologic agent and month —**  **United States, 2001–2002**

* Acute gastrointestinal illness of unknown etiology. 0 2 4 6 8

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Chemical Legionella species AGI* Infectious (other than Legionella species)

.

Month Number of outbreaks



### Campylobacter jejuni outbreak, and an outbreak involvinginfection with two different bacteria (of 12 clinically ill persons, six tested positive for C. jejuni and one tested positive for Yersinia enterocolitica). Illnesses from these three outbreaks resulted in three hospitalizations and no deaths. 

## Water-Quality Data Water-quality data (i.e., information regarding the presence of coliform bacteria, pathogens, or chemical contaminants or data regarding levels of disinfectants such as chlorine) were available for 29 (93.5%) of the 31 outbreaks. Among the 26 0 10 20 30 40 50 60

1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001

Year Individual Noncommunity Community Number of outbreaks **FIGURE 4. Number of waterborne-disease outbreaks** **(n = 758)* associated with drinking water, by year and type of** **water system — United States, 1971–2002**

* Excludes outbreaks of Legionnaires disease.**30 MMWR October 22, 2004**



### outbreaks with a suspected or confirmed infectious etiology, 24 (92.3%) provided bacterial water-quality testing data; a positive total or fecal coliform result from the implicated water was reported for 14 (58.3%) of these 24, including10 (58.8%) of the 17 outbreaks of confirmed infectious etiology, and four (57.1%) of the seven outbreaks of suspected infectious etiology (i.e., AGI). The etiologic organism that caused the outbreak was recovered from the implicated water in 10 (41.7%) of these 24 outbreaks; however, these were theonly 10 outbreaks that were tested specifically for the causative microorganism. Legionella species were detected in the implicated water in all six outbreaks caused by this organism, and etiologic organisms were also recovered from an outbreak of N. fowleri in Arizona (October 2002), from an outbreak of C. jejuni in Wisconsin (January 2001), and from two outbreaks of norovirus in Wyoming (January 2001 and September 2001).

All five reports of outbreaks of chemical etiology providedwater-quality data. In four of these outbreaks, the contaminant that caused the outbreak was recovered directly from theimplicated water, including copper in two outbreaks (Minnesota, November 2001 and Ohio, September 2001), copperand seven other metals in one outbreak (Minnesota, September 2001) and ethyl benzene, toluene, and xylene in one **TABLE 4. Waterborne-disease outbreaks (n = 8) associated with drinking water — United States, 2002**
**No. of Predominant cases Type of**  **State Month Class Etiologic agent illness (n = 432) system* Deficiency** **† Source Setting** 
Arizona Jul I Norovirus Gastroenteritis 71 Com 5 Well Golf Course Arizona Oct I Naegleria fowleri Meningoencephalitis 2 Com 2 Well Community Connecticut Jun I Norovirus Gastroenteritis 142 Ncom 2 Well Camp Florida Sep III AGI § Gastroenteritis, rash 3 Ind 2 Well Household Florida Sep III AGI Gastroenteritis 5 Ind 2 Well Household Kentucky Sep III E. coli O157:H7 Gastroenteritis 2 Ind 2 Well Household New Hampshire Jul III Norovirus Gastroenteritis 201 Ncom 2 Well Camp New York Apr III Giardia intestinalis Gastroenteritis 6 Com 4 Well/spring Trailer park * Com=community; Ncom=noncommunity; Ind=individual. Community and noncommunity water systems are public water systems that serve >15 service

connections or 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 with >15 service connections or an average of >25 residents. A noncommunity water system 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 or schools), whereas transient systems p rovide water to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individ ual water systems are small systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with water notintended for drinking (e.g., lakes, springs and creeks used by campers and boaters, irrigation water, and other nonpotable sources with or without ta ps) are also classified as individual systems. † 1 = untreated surface water; 2 = untreated groundwater; 3 = treatment deficiency (e.g., temporary interruption of disinfection, chronically inadequate

disinfection, and inadequate or no filtration); 4 = distribution system deficiency (e.g., cross-connection, contamination of wa ter mains during construction or repair, and contamination of a storage facility); and 5 = unknown or miscellaneous deficiency (e.g., contaminated bottled wateror storage container). § Acute gastrointestinal illness of unknown etiology.

**TABLE 5. Waterborne-disease outbreaks (n = 9 total; 6 attributed to drinking water) caused by Legionella**  **species — United States, 2001–2002**  **Primary No. of cases State Month/Year Class Etiologic agent Predominant illness water use (n = 282) Setting**  Maryland Oct 2002 III Legionella pneumophila, L. anisa Legionnaires disease Drinking 2 Hospital Massachusetts Jun 2002 III Legionella species Legionnaires disease Drinking 16 Nursing Home Minnesota Feb 2001 III Legionella species Legionnaires disease Drinking 2 Hospital Nevada Feb 2001 I L. pneumophila Legionnaires disease Drinking 20 Hotel Pennsylvania Jun 2002 I Legionella species Legionnaires disease Drinking 12 Nursing home Vermont Jul 2002 III Legionella species Legionnaires disease Drinking 28 Government building complex Illinois* Aug 2002 I Legionella species Pontiac fever Recreational 68 Hotel Ohio † Mar 2001 I Legionella species Legionnaires disease Occupational 17 Automotive plant (Automotive plant) Tennessee § Apr 2002 I L. anisa Pontiac fever Decorative 117 Restaurant (Ornamental fountain)

* This outbreak is discussed in the MMWR Surveillance Summary that discusses recreational water-associated disease outbreaks (Yoder JS, Blackburn BG, Craun GF, et al. Surveillance for waterborne-disease outbreaks associated with recreational water—United States, 2001–2002. In: Surveillance Summaries, October 22, 2004. MMWR 2004;53(No. SS-8):1–21 and is not counted in statistics that summarize drinking water. † This outbreak is discussed in the occupational outbreaks section of this summary and is not counted in statistics that summariz e drinking water. § This outbreak is discussed in the appendix of this summary and is not counted in statistics that summarize drinking water.**Vol. 53 / SS-8 Surveillance Summaries 31**



### outbreak (Florida, September 2001). The contaminant was not recovered from the tested water in an outbreak (Florida, August 2001) that resulted from ethylene glycol contamination caused by a cross-connection during an improperly performed air-conditioning system repair. However, the sample was collected >24 hours after the contaminating event, and a high degree of clinical suspicion of the contaminating agent existed on the basis of the appearance and smell of the water and on the description of the mechanical error. **TABLE 7. Waterborne-disease outbreaks (n = 25) associated with drinking water, by type of deficiency and type of water system (excluding outbreaks caused by**  **Legionella species) — United States, 2001–2002**  **Type of water system*** **Community Noncommunity Individual Total Type of deficiency**  **† No. (%) No. (%) No. (%) No. (%)** 

1: Untreated surface water 000000 **0 0** 2: Untreated groundwater 1 14.3 4 50.0 5 50.0 **10 40.0** 3: Treatment deficiency 1 14.3 2 25.0 4 40.0 **7 28.0** 4: Distribution system 4 57.1 1 12.5 0 0 **5 20.0** 5: Miscellaneous or unknown 1 14.3 1 12.5 1 10.0 **3 12.0 Total 7 100.0 8 100.0 10 100.0 25 100.0**  * Com = community; Ncom = noncommunity; Ind = individual. Community and noncommunity water systems are public water systems that serve >15 service

connections or an average of >25 residents for >60 days/year. A community water system serves year-round residents of a communi ty, subdivision, or mobile home park with >15 service connections or an average of >25 residents. A noncommunity water system can be nontransient o r transient. Nontransient systems serve >25 of the same persons for >6 months of the year, but not year-round (e.g., factories or schools), whereas trans ient systems provide water to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individ ual water systems are small systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with water notintended for drinking (e.g., lakes, springs and creeks used by campers and boaters, irrigation water, and other non-potable sources with or without t aps) are also classified as individual systems. † Examples of treatment deficiencies include temporary interruption of disinfection, chronically inadequate disinfection, or inad equate or no filtration; examples

of distribution system deficiencies include cross-connection, contamination of water mains during construction or repair, or co ntamination of a storage facility; and examples of unknown or miscellaneous deficiences include contaminated bottled water or storage container. **TABLE 6. Waterborne-disease outbreaks (n = 25) associated with drinking water, by etiologic agent and type of water system (excluding outbreaks caused by**  **Legionella species) — United States, 2001–2002**  **Type of water system*** **Community Noncommunity Individual Total**  **Etiologic agent Outbreaks Cases Outbreaks Cases Outbreaks Cases Outbreaks Cases**

**Unknown 0 0 2 98 5 19 7 117**

AGI † 0 0 2 98 5 19 **7 117 Viruses 1 71 4 656 0 0 5 727** 

Norovirus 1 71 4 656 0 0 **5 727 Parasitic 3 14 0 0 2 16 5 30** 

Giardia intestinalis 2 12 0 0 1 6 **3 18** Cryptosporidium species 0 0 0 0 1 10 **1 10** Naegleria fowleri 12 0 0 0 0 **1 2 Chemical 3 33**  **1 4 1 2 5 39**

Copper 2 30 0000 **2 30** Copper and other minerals 0 01400 **1 4** Ethyl benzene, toluene, xylene 0 00012 **1 2** Ethylene glycol 1 30000 **1 3 Bacterial (other than**  **Legionella species) 0 0 1 12 2 15 3 27** 

Campylobacter jejuni 0 0 0 0 1 13 **1 13** C. jejuni and Yersinia enterocolitica 0 0 1 12 0 0 **1 12** Escherichia coli O157:H7 0 00012 **1 2 Total 7 118 8 770 10 52 25 940**  **Percentage (28.0) (12.6) (32.0) (81.9) (40.0) (5.5) (100.0) (100.0)** * Com = community; Ncom = noncommunity; Ind = individual. Community and noncommunity water systems are public water systems thatserve >15 service

connections or 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 with >15 service connections or an average of >25 residents. A noncommunity water system 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 or schools), whereas transient systems p rovide water to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individ ual water systems are small systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with water notintended for drinking (e.g., lakes, springs and creeks used by campers and boaters, irrigation water, and other nonpotable sources with or without ta ps) are also classified as individual systems. † Acute gastrointestinal illness of unknown etiology.**32 MMWR October 22, 2004**



## Water Systems and Water Sources

Because outbreaks caused by Legionellaspecies are not included in statistics resulting from parameters that describe water systems and water sources, they are excluded from this section. The 25 remaining drinking water outbreaks serve as the focus of these parameters.

Seven (28.0%) of these 25 outbreaks were associated withcommunity systems, eight (32.0%) with noncommunity systems, and ten (40.0%) with individual water systems (Tables 6 and 7) (Figure 6). Of the 25 outbreaks, 23 (92.0%) were associated with groundwater sources,including 21 involving wells: one outbreak involved water derived from both a well and spring, and one involved bottled spring water. Two (8.0%) of the25 outbreaks were associated with surface water that derived from a river or

stream.

Among the seven outbreaks associated with community water systems, one (14.3%) was caused by contaminated, untreated groundwater; one (14.3%) was related to a treatment deficiency; and four (57.1%) were related to problems in the water distribution system. One (14.3%) community outbreak of an unknown deficiency resulted in 71 casesof illness when participants at a golf tournament consumed contaminated water and ice. The number of illnesses in the other outbreaks varied (range: 2–28).

Among the eight outbreaks associated with noncommunity water systems, four (50.0%) were caused by contaminated, untreated groundwater; two (25.0%) were related to treatment deficiencies; one (12.5%) was related to a problem in the water distribution system; and one (12.5%) had an unknown deficiency.

Among the 10 outbreaks associated with individual water systems, five (50.0%) were caused by contaminated, untreatedgroundwater; four (40.0%) were related to treatment deficiencies; and one (10.0%) had an unknown deficiency. These outbreaks affected limited populations (range: 2–13 cases).

All three of the bacterial (other than Legionellaspecies) outbreaks occurred in association with groundwater systems (allwere untreated wells). Four (80.0%) of the five parasitic outbreaks occurred in association with groundwater systems: two **TABLE 8. Waterborne-disease outbreaks (n = 25) associated with drinking water, by type of deficiency and source (excluding outbreaks caused by**  **Legionella species) — United States, 2001–2002** 
**Source**
**Groundwater Surface water Total** **Type of deficiency* No. (%) No. (%) No. (%)**

1: Untreated surface water 0000 **0 0** 2: Untreated groundwater 10 43.5 0 0 **10 40.0** 3: Treatment deficiency 6 26.1 1 50.0 **7 28.0** 4: Distribution system 4 17.4 1 50.0 **5 20.0** 5: Miscellaneous or unknown 3 13.0 0 0 **3 12.0 Total 23 100.0 2 100.0 25 100.0**  * Examples of treatment deficiencies include temporary interruption of disinfection, chronically inadequate disinfection, or ina dequate or no filtration; examples

of distribution system deficiencies include cross-connection, contamination of water mains during construction or repair, or co ntamination of a storage facility; and examples of unknown or miscellaneous deficiences include contaminated bottled water or storage container.

**FIGURE 6. Drinking water-associated outbreaks, by etiologic agent, water system, water source, and deficiency — United States, 2001–2002** 
Etiologic agent (n = 31)

Unidentified

22.6% Legionella species 19.4%

Bacterial*

9.7%

Parasitic 16.1% Viral 16.1% Chemical 16.1% Noncommunity 32.0%

Community

28.0% Individual

40.0% Water system (n = 25) †

Groundwater 92.0%

Surface water 8.0% Water source (n = 25) †

Treatment deficiency

28.0% Untreated groundwater

40.0%

Distribution system 20.0% Miscellaneous 12.0% Deficiency § (n = 25) †

* Other than Legionella species. † Excludes outbreaks attributed to Legionella species. § No outbreaks were attributed to untreated surface water.**Vol. 53 / SS-8 Surveillance Summaries 33**



### were associated with untreated wells; one occurred after the homeowners intentionally bypassed a reverse osmosis system that had run out of treated water; and one was associated with a distribution deficiency in a treated well/spring combination source. All five viral outbreaks occurred in association with groundwater systems: three were associated with untreatedwells; one was related to a treatment deficiency in a chlorinated well; and one had an unknown deficiency. Four (80.0%) of the five chemical outbreaks occurred in association withgroundwater systems: three were related to distribution system deficiencies in well water, and one was related to an unknown deficiency in a bottled water product that had a spring as its source. All seven outbreaks of unknown etiology were linked to groundwater systems: four were associated with treatment deficiencies of chlorinated wells, and three were associated with unknown deficiencies in wells (one chlorinated and two untreated).

Among the 23 outbreaks related to groundwater systems,10 (43.5%) were linked to consumption of untreated groundwater, six (26.1%) were associated with treatment deficiencies; four (17.4%) were linked to deficiencies in the distribution system; and three (13.0%) had unknown deficiencies (Table 8). Among the two outbreaks related to surface water systems, one (50.0%) was caused by a treatment deficiency and one (50.0%) by a distribution system deficiency.


## Outbreaks Caused by Legionellaspecies

Drinking Water Legionella Outbreaks

During 2001–2002, six Legionella outbreaks were relatedto water systems in which the primary water use at the outbreak site was for drinking (Table 5). These outbreaks caused illness in 80 persons and resulted in 41 hospitalizations and four deaths. The predominant clinical syndrome in all six outbreaks was Legionnaires disease, although in one outbreak involving a government building complex in Vermont (July2002), six (21.4%) of the 28 ill persons had symptoms consistent with the case definition for Pontiac fever. All of these outbreaks occurred in large buildings or institutional settings and were related to multiplication of Legionella species in the respective distribution systems.

Other Legionella Outbreaks

One Legionella outbreak was related to a water system inwhich the primary water use at the outbreak site was recreational (Table 5); this outbreak is discussed elsewhere ( 8). One Legionella outbreak occurred in an occupational setting and is discussed in the following section. Another Legionellaoutbreak occurred in Tennessee in April 2002 (32) (Appendix) when patrons of a restaurant experienced Pontiac fever in association with sitting near a particular fountain in the restaurant. Cultures from the fountain were positive for L. anisa

. No foods or other exposures were associated with illness, and the restaurant’s air conditioning system was negative for Legionella species on laboratory testing. This outbreak caused illness in 117 persons and led to one hospitalization.



## Outbreaks Associated with Occupational Exposure to Water

Two outbreaks associated with exposure to water in an occupational setting were reported during 2001–2002. In November 2002, a worker at a wastewater treatment plant in California fell into an equalization basin containing untreated wastewater and subsequently contracted giardiasis. A coworker subsequently experienced gastrointestinal symptoms, although his illness went undiagnosed. In March 2001, an outbreak of Legionnaires disease occurred at an automotive plant in Ohio (33 ) in which contact with the cleaning area of the plant (particularly one cleaning line) was associated with disease. As a result of this outbreak, 17 persons became ill, two of whom died.


## Previously Unreported Outbreaks

Reports of three previously unreported drinking water outbreaks that occurred during 2000 were received during this reporting period (Table 9). An outbreak of cryptosporidiosis occurred in Florida in December 2000 when a groundwater system experienced a main break days before the first of a cluster of five cases of gastrointestinal illness. Cryptosporidium was subsequently identified in a stool specimen from one of these patients. Reports of outbreaks of norovirus (Kansas, June 2000) and cholera (Marshall Islands, December 2000) were also received during this reporting period (Appendix).



## Outbreaks Not Classified as WBDOs

Epidemiologic evidence from four additional outbreaks that were reported as potentially associated with drinking water during 2001–2002 was insufficient to warrant counting these outbreaks as WBDOs. However, because of their potential links to drinking water, a brief description of these outbreaks follows.

In June 2002, an outbreak of diarrheal illness occurred among 38 climbers of Mt. Denali in Alaska; illness lasted amean of 2 days (range: 1–5 days), and the attack rate of climbers was 27% during the 3-day study period. The hypothesized cause was use of fecally contaminated snow as a drinking water source, but this was not associated with illness in a cohort study that was performed during the outbreak.**34 MMWR October 22, 2004**



### In June 2002, two persons in a Florida household supplied by an untreated well experienced recurring oral lesions and pharyngitis. A third person in the household who did not drink from this water source remained asymptomatic. Although the well water was positive for fecal coliforms, no other epidemiologic evidence linked the drinking water to illness.

In June 2002, >77 rafters on the Colorado River in Grand Canyon National Park in Arizona became ill with diarrhea and other gastrointestinal symptoms. Norovirus was isolated from stool specimens of seven (53.8%) of the 13 persons tested. Although norovirus was identified in samples of river water and water from a sewage treatment plant that emptied into the river, these were not the same strains identified in the stool samples. However, a weak association was identified between drinking river water and illness, and no other exposures (e.g.,food contamination or asymptomatic carriers) were associated with illness.

In April 2000, an outbreak of cholera that sickened approximately 3,500 persons and caused 20 deaths began on Pohnpei Island in the Federated States of Micronesia. No information is available as to the cause of the outbreak or the risk factors for illness.



## Discussion

Considerations Regarding Reported Results

The WBDO surveillance system provides information concerning epidemiologic and etiologic trends in outbreaksrelated to drinking water. However, not all outbreaks are recognized, investigated, or reported to CDC or EPA, and studies have not been performed that assess the sensitivity of this system. Furthermore, outbreaks occurring in national parks, tribal lands, or military bases might not be reported to state or local authorities. For these reasons, the true incidence of WBDOs is probably greater than is reflected in surveillance system data. Multiple factors influence whether WBDOs arerecognized and investigated by local or state public health agencies, including public awareness of the outbreak, availability of laboratory testing, requirements for reporting diseases, and resources available to local health departments for surveillance and investigation of probable outbreaks. In addition, becausechanges in the capacity of local and state public health agencies and laboratories to detect an outbreak might result in reporting and surveillance bias, the states with the majority of outbreaks reported during this period might not be the states in which the majority of outbreaks actually occurred. An increase or a decrease in the number of outbreaks reported might reflect either an actual increase or decrease in outbreaks or a change in sensitivity of surveillance practices. As with any passive surveillance system, accuracy of the data depends greatly on the reporting agencies (i.e., state, local, and territorial healthdepartments). Thus, independent of the recognition or investigation of a given outbreak, reporting bias can also influence the final data.

Outbreaks most likely to be recognized and investigated arethose involving acute illness characterized by a short incubation period, serious illness or symptoms requiring medical treatment, or recognized etiologies for which laboratory methods have become more sensitive or widely available. Increased reporting often occurs as etiologies become better recognized, water system deficiencies are identified, and state surveillance activities and laboratory capabilities increase (34–36). Recommendations for improving WBDO investigations include increased laboratory support for clinical and water analyses, enhanced surveillance activities, and assessment of sources of potential bias (37–39 ). **TABLE 9. Waterborne-disease outbreaks (n = 3) associated with drinking water that were not included in previous surveillance summaries**  **Predominant No. of cases Type of** **State/territory Month, year Class Etiologic agent illness (n = 194) system* Deficiency** **† Source Setting** 

Florida December 2000 III Cryptosporidium species Gastroenteritis 5 Com 4 Well Community Kansas June 2000 I Norovirus Gastroenteritis 86 Ncom 2 Well Cabin Republic of

Marshall Islands December 2000 II Vibrio cholerae Gastroenteritis 103 Ind 5 Unknown Community * Com = community; Ncom = noncommunity; Ind = individual. Community and noncommunity water systems are public water systems thatserve >15 service

connections or 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 with >15 service connections or an average of >25 residents. A noncommunity water system 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 or schools), whereas transient systems p rovide water to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individ ual water systems are small systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with water notintended for drinking (e.g., lakes, springs and creeks used by campers and boaters, irrigation water, and other nonpotable sources with or without ta ps) are also classified as individual systems. † 1 = untreated surface water; 2 = untreated groundwater; 3 = treatment deficiency (e.g., temporary interruption of disinfection, chronically inadequate

disinfection, and inadequate or no filtration); 4 = distribution system deficiency (e.g., cross-connection, contamination of wa ter mains during construction or repair, and contamination of a storage facility); and 5 = unknown or miscellaneous deficiency (e.g., contaminated bottled wateror storage container).**Vol. 53 / SS-8 Surveillance Summaries 35**



### The identification of the etiologic agent of a WBDOdepends on the timely recognition of the outbreak so appropriate clinical and environmental samples can be collected.Additionally, the laboratory involved must have the capability to test for an organism to detect it. For example, routine testing of stool specimens at laboratories include tests for the presence of enteric bacterial pathogens and might also include an ova and parasite examination. However, Cryptosporidium species, among the most commonly reported waterbornepathogens, are often not included in standard ova and parasite examinations and thus should be specifically requested ( 40). Additionally, although norovirus testing is being performed more commonly, testing for other viral agents is rarelydone. Finally, collection of water-quality data depends primarily on local and state statutory requirements, the availability of investigative personnel, and the technical capacity of the laboratories that test the water.

One key limitation of the data collected as part of the WBDO surveillance system is that the information collected pertains only to outbreaks of waterborne illness rather than endemic waterborne illness. The epidemiologic trends andwater-quality concerns observed in outbreaks might not necessarily reflect or correspond with trends associated withendemic waterborne illness. CDC and EPA have recently completed a series of epidemiologic studies designed to assess themagnitude of endemic waterborne illness associated with consumption of municipal drinking water. A joint report on the results of these studies is forthcoming.


## Drinking Water Outbreaks Caused by Legionella species

Of the 31 drinking water-associated outbreaks that occurred during 2001–2002, six (19.4%) were caused by Legionellaspecies, which was the single most commonly identified etiologic agent. Because this is the first time that LD outbreaks have been included in the MMWR Surveillance Summary of WBDOs, no comparative data are available from previous reporting periods. LD outbreaks tended to result in higher morbidity and mortality than the majority of other outbreaks reported (as evidenced by the hospitalization and case-fatality rates) and differed epidemiologically from other drinking water outbreaks. They fit patterns usually seen with Legionella (i.e., they all occurred in large buildings or institutional settings, were related to amplification of Legionellaspecies in the respective distribution systems, and were most likely spreadby aerosolization of water from these systems). Contamination of source water is less likely to lead to outbreaks involving this organism. These outbreaks underscore the importance of remaining vigilant about the possibility of Legionella species in any building complex and the need to take measures that address this threat (e.g., maintaining hot water temperatures of >124 o 

### F [ return temperature]/>140 o 

### F [storage temperature] and cold water storage and distribution temperatures <68 o 

### F, testing for this organism when outbreaks of respiratory disease or febrile illness occur in these settings, and maintaining adequate disinfectant levels as appropriate) ( 41,42).


## Drinking Water Outbreaks (Excluding Those Caused by Legionella species)

Because of the different epidemiology of Legionella outbreaksand because LD outbreaks have not been included in previous summaries, they will not be discussed in the followingsections, which address the remaining 25 drinking water outbreaks that occurred during 2001–2002. These 25 outbreaks represent a 35.9% decrease from the 39 outbreaks reported during 1999–2000 (2), which was the highest total reported in 8 years ( 2–7 ). Seasonality of drinking water outbreaks remained consistent with previous years, with the highest number of outbreaks reported during June–September.

The number of reported outbreaks began to decrease sharply beginning with the 1985–1986 reporting period; this wasattributable primarily to fewer community and noncommunity outbreaks. With institution and enforcement of betterregulations that chiefly affect these types of water systems (particularly community systems), a marked drop in the number of outbreaks was seen. In contrast, the increase in outbreaks reported during 1999–2000 was attributable primarily to individual water systems, which affect fewer persons, are less regulated, and are more subject to changes in surveillance andreporting. The relative proportion of community, noncommunity, and individual outbreaks during 2001–2002 was more consistent with historic norms, as was the total number of outbreaks.

During 2001–2002, Florida reported the highest number of outbreaks (eight), as was the case during 1999–2000, when 15 outbreaks were reported. The only other state to report >2 drinking water-associated outbreaks during 2001–2002 was Minnesota, with three outbreaks. Reports of these outbreaks might reflect enhanced surveillance activities rather than a true increase in WBDO incidence; six outbreaks in Florida during 2001–2002 and 14 during 1999–2000 occurred in a single county and were investigated by the same epidemiologist. Among the five most populous states (California, Florida,Illinois, New York, and Texas), only Florida reported >1 drinking water-associated outbreak; California and Texas reported none, and Illinois and New York each reported one. Similarly, in the 2001–2002 summary of recreational water-associated**36 MMWR October 22, 2004**



### outbreaks ( 8), Florida and Minnesota reported more recreational water-associated outbreaks than any other state (sevenand nine, respectively). This suggests that reporting and surveillance bias might be influencing the number of reports, resulting in considerable year-to-year and state-to-state variation.

Surface Water

Two (8.0%) of the 25 drinking water-associated outbreaks during 2001–2002 were associated with systems served bysurface water (Figure 6), compared with seven (18.4%) during 1999–2000. Among the two surface water-related outbreaks, one was an outbreak of copper poisoning (Ohio, 2001) related to a distribution system deficiency, and one was an outbreak of giardiasis in a rural Colorado town during 2001caused by the failure of a bag filtration system. The latter outbreak is the first associated with inadequate treatment of surface water to occur in a community system since 1997, when an outbreak of giardiasis associated with disinfected but unfiltered surface water occurred in New York (3 ). The last community system-associated outbreak related to inadequate filtration of surface water occurred during 1995, when a large outbreak of giardiasis was reported in New York ( 4). In contrast, during 1991–1994, eight outbreaks (including a substantial outbreak in Milwaukee) were reported in community systems that used treated surface water ( 5,6 ). The decrease in outbreaks associated with inadequate treatment of surface water sources is likely attributable to increasingly stringent regulations for treatment of surface water. However, even with the additional EPA regulations, outbreaks might still occur. For example, in addition to the giardiasis outbreak reportedin Colorado during 2001, another limited outbreak of giardiasis was reported in a Colorado resort during 1999–2000 (2); this outbreak was attributed in part to defective cartridgefilters. The Colorado outbreaks underscore the need for cartridge, bag, and other package filters to meet design specifications and be properly installed if they are to be effective. All filtered systems, no matter what type of filter is employed, should be adequately operated, maintained, and monitored to ensure reliable performance.

During 2001–2002, no outbreaks were associated with the direct ingestion of untreated surface water, compared with three outbreaks during 1999–2000. This is encouraging, because keeping the public aware that surface water, despite its clarity, is prone to contamination by pathogens and should not be directly consumed without being treated at the pointof use or boiled, remains a priority. Manufacturers of pointof-use devices and the National Sanitation Foundation provide information (available at http://www.nsf.org) regarding different devices, instructions for use, and their ability to make water safe for human consumption. Groundwater Of the 25 outbreaks related to drinking water, 23 (92.0%) were associated with groundwater sources, compared with 28 (73.7%) during 1999–2000 (2 ). Of the 25 reported outbreaks, 10 (40.0%) were linked to consumption of contaminated, untreated groundwater. During 1999–2000, a total of 17 (44.7%) of 38 outbreaks were associated with contaminated, untreated groundwater sources. Although outbreaks caused by the use of untreated groundwater decreased during 2001–2002, the largest proportion of groundwater outbreaks during this period remained attributable to untreated water systems, and untreated groundwater remains a primary cause of outbreaks, especially in private, individual water systems that are not regulated by EPA. During both the current and pervious reporting periods, half of the outbreaks attributed to untreated groundwater were reported in individual water
systems.

Treated groundwater systems can also lead to outbreaks; six(24.0%) of the 25 outbreaks during 2001–2002 were associated with treatment deficiencies of groundwater systems (including one outbreak in which treatment was bypassed), compared with eight (21.1%) during 1999–2000. Four(66.7%) of the six outbreaks associated with treated groundwater during 2001–2002 were reported in individual rather than public systems, compared with one outbreak (14.3%) during 1999–2000. To safeguard the quality of their well water,homeowners should purchase appropriately designed pointof-use devices and follow instructions for operating and maintaining these treatment devices. Public health agencies can helpby providing educational materials about effective water treatment devices for private, individual water systems. Although individual groundwater systems are not regulated by EPA, and public groundwater systems (other than systems influencedby surface water) are not required to filter or disinfect drinking water, efforts should continue to identify and remove possible sources of contamination and provide adequate, continuous treatment for those systems that need treatment. Wells and springs must be protected from contamination evenif disinfection is provided, as groundwater can become contaminated with pathogens that might overwhelm the disinfection process. EPA’s proposed GWR (information available at http://www.epa.gov/safewater/gwr.html) is expected to establish multiple barriers in groundwater systems to protect against pathogens in drinking water from groundwater sources and should establish a targeted strategy to identify groundwater systems at high risk for fecal contamination. The multiple barrier approach should begin with protection of thewellhead, an assessment of potential sources of contamination, and periodic sanitary surveys to ensure that wells remain protected. Periodic monitoring of source water is necessary to**Vol. 53 / SS-8 Surveillance Summaries 37**



### identify water-quality deterioration, and adequate, continuous water treatment is needed for wells that are identified as being vulnerable.

Of the 22 well-related outbreaks that occurred during 2001– 2002, a total of 13 (59.1%) were associated with community or noncommunity wells, compared with nine (40.9%) thatwere associated with individual wells not covered by EPA regulations. This distribution, similar to previous reporting periods, is notable because only public water systems will be directly affected by GWR, and thus protections offered by GWR might not extend to individual groundwater systems.The quality of water in private wells and springs used by private persons and nonpublic systems thus remains a public health concern; approximately 17 million persons in the United States rely on private household wells for drinking watereach year, and >90,000 new wells are drilled annually throughout the United States ( 43 ). In addition, contamination of a private well is not only a health concern for the householdserved by the well but can have an impact on households using other nearby wells that draw from the same aquifer. EPA does not regulate private wells and will not do so as part of theproposed GWR. EPA recommendations for protecting private water supplies are available at http://www.epa.gov/ safewater/pwells1.html. Additional efforts should be taken to educate well owners, users, well drillers, and local and state drinking water personnel to encourage practices that best ensure safe drinking water for private well users.

Deficiencies

During 2001–2002, the number of outbreaks associated with each different type of deficiency (untreated surface water,untreated groundwater, treatment deficiency, distribution system deficiency, and unknown/miscellaneous deficiency)decreased from levels reported during 1999–2000. In addition, each deficiency type represented a similar proportion of the total number of drinking water outbreaks reported during 1999–2000.
Water Systems

During 2001–2002, the number of outbreaks associated with each of the three different types of water systems also decreased compared with 1999–2000 (Figure 6), whereas theproportion associated with each type remained relatively consistent. The number of outbreaks associated with individual systems decreased from 17 during 1999–2000 to 10 during 2001–2002, but still remained the most common of the three. Of the eight outbreaks reported from Florida (the state with the most reported outbreaks, possibly reflecting enhancedsurveillance in that state), seven involved individual groundwater systems (the eighth involved a community well system), which might have biased the results toward more individual(as well as more groundwater) outbreaks; this again potentially demonstrates that outbreaks involving individual water systems are the most susceptible to detection bias, given the limited number of persons involved, the different levels ofresources available to investigate these outbreaks, and the limited number of regulations that govern these systems. The number and proportion of outbreaks attributed to individualsystems during 1999–2000 was at a 15-year high and accounted for much of the overall increase in the number ofoutbreaks reported during 1999–2000. The decline in outbreaks attributed to individual systems makes the number and proportion of outbreaks associated with each type of water system more comparable with reporting periods during the 1990s. Etiologic Agent

The etiologic agent was not identified in seven (22.6%) of the 31 outbreaks reported during 2001–2002 (Figure 6). Although these seven outbreaks comprised the largest group of outbreaks, this was a marked decrease from the number(17) and percentage (43.6%) of outbreaks of unknown etiology during 1999–2000. This likely reflects both the improved diagnostic capability of laboratories and better outbreak investigations, resulting in more rapid and more appropriate specimen collection. Viral outbreaks (five) comprised 16.1% of the total, an increase from the previous reporting period. This likely reflects rapidly improving diagnostic capability for detecting norovirus in stool samples, a hypothesis supported by the fact that all five viral outbreaks were caused by this agent. The five norovirus outbreaks affected by far the most persons (727) of any single etiologic agent and caused more illness than all other agents combined. Parasitic outbreaks (five) also comprised 16.1% of the total, similar to previous years. Among the parasitic outbreaks, two linked cases of N. fowleri infection occurred in Arizona during October 2002, resulting in two deaths; this was the first report of an outbreak of N. fowleri in the United States related to a drinking water system (Appendix). This outbreak further underscores the need for treatment of groundwater, particularly in geothermal areas in which these thermophilic amebae are likely to be amplified. Chemical outbreaks (five) also comprised 16.1% of the total, an increase from the previous reporting period;these outbreaks highlight the importance of proper maintenance of water systems, because four of the five resulted directly from errors related to either recent maintenance work or to an improperly installed device. Bacterial outbreaks (three) comprised 9.7% of the total, a decrease compared with the previous reporting period and the lowest number reported since 1991–1992.**38 MMWR October 22, 2004**



## Conclusion
Data collected as part of the national WBDO surveillance system are used to describe the epidemiology of waterborne diseases in the United States. Trends regarding water systems and deficiencies implicated in these outbreaks are used toassess whether regulations for water treatment and monitoring of water quality are adequate to protect the public’s health.Identification of the etiologic agents responsible for these outbreaks is also critical because new trends might necessitate different interventions and changes in policies and resource allotment.

Surveillance for waterborne agents and outbreaks occurs primarily at the local and state level. Local and state publichealth authorities should be able to detect and recognize drinking water-associated outbreaks and implement appropriate prevention and control measures. Improved communication among local and state public health departments, regulatory agencies, water utilities, and recreational water facilities wouldaide the detection and control of outbreaks. Routine reporting or sharing of water-quality data with the health department is recommended. Other means of improving surveillanceat the local, state, and federal level might include the 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).

State health departments can request epidemiologic assistance and laboratory testing from CDC to investigateWBDOs. CDC and EPA can be consulted regarding engineering and environmental aspects of drinking water and recreational water treatment and regarding collection of large-volume water samples to identify pathogenic viruses and parasites, which require special protocols for their recovery. Requests for tests for viral organisms should be made to CDC’s Viral Gastroenteritis Section, Respiratory and Enterovirus Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases (NCID), at 404-639-3577. Requests for information or testing for Legionella should be made to CDC’s Respiratory Diseases Branch, Division of Bacterial and Mycotic Diseases, at 404-639-2215. Requests for tests for parasites should be made to CDC’s Division of Parasitic Diseases, NCID, at 770-488-7756.

Additional information is available from • EPA’s Safe Drinking Water Hotline at 800-426-4791, on

the Internet at http://www.epa.gov/safewater, or by e-mail at hotline-sdwa@epa.gov; • CDC’s DPD drinking water website at http://

www.cdc.gov/ncidod/dpd/healthywater/index.htm;• CDC’s Cryptosporidiosis Information Line of the Parasitic Disease Information Line at 888-232-3228 (voice system) or 888-232-3299 (fax system); and • for reporting WBDOs, CDC’s Division of Parasitic Diseases, NCID, at 770-488-7756 or by fax at 770-488-7761; an electronic version of CDC’s reporting form (CDC 52.12, rev. 01/2003) is available at http://www.cdc.gov/ healthyswimming/downloads/cdc_5212_waterborne.pdf.

Acknowledgments The authors thank the following persons for their contributions to this report: state waterborne-disease surveillance coordinators; state epidemiologists; state drinking water administrators; Robert Tauxe, M.D., Matt Moore, M.D., Barry Fields, Ph.D., Rachel Woodruff, M.P.H., Division of Bacterial and Mycotic Diseases, NCID, CDC; Marc-Alain Widdowson, M.A., Vet.M.B., M.Sc., Division of Viral and Rickettsial Diseases, NCID, CDC; Matthew Arduino, Dr.P.H. Joe Carpenter, Division of Healthcare Quality and Promotion, NCID, CDC; Mark Eberhard, Ph.D., James Maguire, M.D., Adria Prosser, Ph.D., Division of Parasitic Diseases, NCID, CDC; Lorraine Backer, Ph.D., Mark McClanahan, Ph.D., Division of Environmental Hazards and Health Effects, NCEH, CDC.

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for waterborne disease outbreaks—United States, 1999–2000. In: CDC Surveillance Summaries, November 22, 2002. MMWR 2002;51 (No. SS-8):1–47.3. Barwick RS, Levy DA, Craun GF, Beach MJ, Calderon RL. Surveillance for waterborne disease outbreaks—United States, 1997–1998. In: CDC Surveillance Summaries, May 26, 2000. MMWR 2000;49(No. SS-4):1–34.4. Levy DA, Bens MS, Craun GF, Calderon RL, Herwaldt BL. Surveillance for waterborne-disease outbreaks—United States, 1995–1996. In: CDC Surveillance Summaries, December 11, 1998. MMWR 1998;47(No. SS-5):1–34. 5. Kramer MH, Herwaldt BL, Craun GF, Calderon RL, Juranek DD.

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Juranek DD. Surveillance for waterborne disease outbreaks—United States, 1991–1992. In: CDC Surveillance Summaries, November 19, 1993. MMWR 1993:42(No. SS-5):1–22. 7. Herwaldt BL, Craun GF, Stokes SL, Juranek DD. Waterborne-disease

outbreaks, 1989–1990. In: CDC Surveillance Summaries, December 1991. MMWR 1991;40(No. SS-3):1–21. 8. Yoder JS, Blackburn BG, Craun GF, et al. Surveillance for recreational

water-associated outbreaks—United States, 2001–2002. In: Surveillance Summaries, October 22, 2004. MMWR 2004;53(No. SS-8):1–21. 9. Environmental Protection Agency. 40 CFR Part 141. Water programs:

national interim primary drinking water regulations. Federal Register 1975;40:59566–74.10. Pontius FW, Roberson JA. Current regulatory agenda: an update. Journal of the American Water Works Association 1994;86:54–63.**Vol. 53 / SS-8 Surveillance Summaries 39**

11. Pontius FW. Implementing the 1996 SDWA amendments. JAWWA 1997;89:18–36. 12. Environmental Protection Agency, 40 CFR Parts 9, 141, and 142. National primary drinking water regulations; arsenic and clarifications to compliance and new source contaminants monitoring. Federal Register 2001;66:1–92. 13. Environmental Protection Agency, 40 CFR Parts 9, 141, and 142. National primary drinking water regulations for lead and copper; final rule. Federal Register 2000;65:1949–2015.14. Environmental Protection Agency. 40 CFR Parts 141 and 142. Drinking water; national primary drinking water regulations; total coliforms (including fecal coliforms and E. coli); final rule. Federal Register 1989;54:27544–68.15. Environmental Protection Agency. 40 CFR Parts 141 and 142. Drinking water; national primary drinking water regulations; total coliforms; corrections and technical amendments; final rule. Federal Register 1990;55:25064–5.16. Environmental Protection Agency. 40 CFR Parts 141 and 142. Drinking water; national primary drinking water regulations; filtration, disinfection; turbidity, Giardia lamblia , viruses, Legionella , and heterotrophic bacteria; final rule. Federal Register 1989;54:27486–541. 17. Environmental Protection Agency. 40 CFR Parts 9, 141, and 142.National primary drinking water regulations: interim enhanced surface water treatment; final rule. Federal Register 1998;63:69478–521. 18. Environmental Protection Agency. 40 CFR Parts 9, 141, and 142. National primary drinking water regulations: long term 1 enhanced surface water treatment rule; final rule. Federal Register 2002;67:1812–44. 19. Environmental Protection Agency. 40 CFR Parts 9, 141, and 142. National primary drinking water regulations: long term 1 enhanced surface water treatment and filter backwash rule; proposed rule. Federal Register 2000;67:19046–150. 20. 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GAO/RCED-97-123.**40 MMWR October 22, 2004** 

# Appendix Selected Case Descriptions of Outbreaks Associated with Drinking Wate r

**State in which Suspected Number**  **Outbreak outbreak or confirmed of persons date occurred etiologic agent affected Case description** 

Arizona

Indiana

New York

Alaska

Republic of Marshall Islands* **Bacteria** October 2002

August 2001

April 2002

June 2001

December 2000 Naegleria fowleri

Cryptosporidium species

Giardia intestinalis

Campylobacter jejuni and Yersinia enterocolitica

Vibrio cholerae 2

10

6

12

103 **Parasites**

Two previously healthy children from the same neighborhood died of meningoencephalitis within 1 day of each other; N. fowleri was identified at autopsy in brain tissue of both children. Neither child had any contact with recreational water during the incubation period except at their own or family members’ private homes (untreated water in a bathtub and a swimming pool), and the two families did not associate with each other. Drinking water for the respective families came from the same untreated community well water system, and testing revealed N. fowleri in both a storage tank connected to one of the wells, and from the refrigerator filter of the house in which one of the children was exposed. The water was also positive for total coliforms. N. fowleri contaminating the aquifer, well, or distribution system might have been delivered to each home during the exposure period. This is the first association of a drinking water system with N. fowleri infection in the United States.

A reverse osmosis filtration system that was normally used to treat well water was intentionally bypassed when attendees of a party ran low on purified water. Attendees of the party who drank the untreated water subsequently experienced illness. The well was in a high-density septic tank area.

Water became contaminated at a trailer park, causing residents to become ill. Contamination was attributed to a power outage, which created a negative pressure condition in the distribution system. This allowed contaminated water to enter the system through either a cross connection inside a mobile home or a leaking underground pipe that was near sewer crossings.

Cannery workers who lived at a bunkhouse became ill when a well that supplied the bunkhouse became contaminated with surfacewater. This drinking water had become yellow tinged and malodorous just before the outbreak, and illness was associated with living in the bunkhouse and drinking water there. Well water tested positive for fecal coliforms; no chemical disinfectant had been used, and a filter of unknown efficacy against common pathogens had been used. Stool samples from six persons tested positive for C. jejuni, and those from one person tested positive for Y. enterocolitica.

Local residents of a small island became ill because of problems with the handling, transport, and storage of water from one of their primary drinking water sources (i.e., chlorinated water from a U.S. military base on a neighboring island). Residents collected and transported this water themselves to their island; illness was associated with drinking this water, whereas consuming bottled water or drinking water that was boiled or treated with flavored citric acid drink mixes (pH 3.4–3.9) was protective. Also protective was the use of vessels that could be tightly sealed and from which water could be poured without opening the vessel. No foods were associated with illness. Three of thirty stool specimens tested among persons with diarrhea were positive for V. cholerae , and69% of case-patients tested positive for antibodies to this pathogen. Six persons died. Water from the base was not tested for V. cholerae but was determined to have adequate chlorine levels. Contamination likely occurred because of the use of loosely sealed vessels during storage, unsafe handling, and transport of the water**Vol. 53 / SS-8 Surveillance Summaries 41**

**State in which Suspected Number**  **Outbreak outbreak or confirmed of persons date occurred etiologic agent affected Case description** 
from one island to the other. ( **Source:** Beatty ME, Jack T, Sivapalasingam S, et al. An outbreak of Vibrio cholerae O1 infections on Ebeye Island, Republic of the Marshall Islands, associated with use of an adequately chlorinated water source. Clin Infect Dis 2004;38:1–9.)

Members of a book group attended lunch at a private home as partof a tour. Thirteen persons subsequently experienced gastrointestinal symptoms; all of six stools tested for bacteria were positive for C. jejuni . Exposure to well water was associated with illness, and on laboratory testing the water was positive for C. jejuni . Surface water contamination of a shallow, untreated well was thought to be the likely cause of the outbreak; the well was located next to a chicken coop.

Residents and an employee of a nursing facility contracted Legionnaires disease over a 2-week period. Laboratory testing for Legionella was positive in samples from the water distribution system. A watermain break was reported near the facility 1 month before the outbreak and might have allowed introduction of Legionella into the system.

One hospital employee and a patient became ill with Legionnaires disease; in the previous two years, three other infections had occurred. An environmental investigation found L

. pneumophila in potable water from showers and sinks in a hospital room and recovery room. Possible multiplication of L

. pneumophila occurred in dead ends of the plumbing system.

Cases of Legionnaires disease occurred among hotel guests during an 8-month period; one person died. Illness was associated with residing in a particular tower of the hotel. Showering for longer times during the day was also associated with illness. An L. pneumophila isolate identical to the clinical isolates was found in potable water throughout the implicated hotel tower, and L. pneumophila isolates that differed from the clinical isolates were identified in all cooling towers at the hotel.

Workers at an automotive engine manufacturing plant experienced Legionnaires disease during a 1-month period; two persons died. Contact with the cleaning area of the plant was a risk factor for disease, and one cleaning line in particular was associated with the highest risk. Legionella species were recovered from multiple environmental samples, although the subtype present in the patients was not recovered from the environmental samples. ( **Source:** Fry AM, Rutman M, Allan T, et al. Legionnaires’ disease outbreak in an automobile manufacturing plant. J Infect Dis 2003;187:1015–8.)

Residents and an employee of a nursing facility contracted Legionnaires disease during a 1-month period; two persons died. Residence in a particular wing of the facility was associated with illness, as was frequent bathing or bathing during 2 particular days. Testing of potable water samples revealed no chlorine residual, and Legionella species were cultured from multiple water distribution sites, including a hot water holding tank, showers, sinks, and bathtubs; Legionella was not recovered from the cooling tower associated with the facility. Before the outbreak, water was shut off to part of the facility, causing a temporary decrease in water pressure. 13

16

2

20

17

12 C. jejuni

Legionella species

Legionella species

L. pneumophila

Legionella species

Legionella species Wisconsin

Massachusetts

Minnesota

Nevada

Ohio †

Pennsylvania January 2001

June 2002

February 2001

February 2001

March 2001

June 2002**42 MMWR October 22, 2004**

**State in which Suspected Number**  **Outbreak outbreak or confirmed of persons date occurred etiologic agent affected Case description** 

**Viruses** 117

71

142

86

230 April 2002

July 2002

June 2002

June 2000

January 2001 Tennessee §

Arizona

Connecticut

Kansas*

Wyoming L. anisa

Norovirus

Norovirus

Norovirus

Norovirus Patrons of a restaurant experienced Pontiac fever during a 1-week period. Illness was associated with sitting near a particular fountain, and cultures from that fountain were positive for L. anisa. Water in the fountains is recirculated for filtration and disinfection with bromine; environmental investigation identified areas in fountain pools where water may not have been recirculated. No foods or other exposures were associated with illness. The restaurant’s air-conditioning system was negative for Legionella species on laboratory testing. One person was hospitalized, and no deaths occurred. ( **Source:** Jones TF, Benson RF, Brown EW, Rowland JR, Crosier SC, Schaffner W. Epidemiologic investigation of a restaurant-associated outbreak of Pontiac fever. Clin Infect Dis 2003;37:1292–7.)

The outbreak occurred among users and employees of a golf course. Exposure to golf course drinking water was significantly associated with illness. Ice and water dispensers and ice-making facilities were not safely maintained and not properly cleaned and sanitized. One death occurred because of aspiration of vomitus. Norovirus was detected by polymerase chain reaction (PCR) in stool specimens from three of nine persons.

Attendees of a camp became ill when a large well system likely became contaminated after heavy rains; well water samples were positive for total coliforms and Escherichia coli . The outbreak ended within 2 days of chlorinating the water supply and provision of alternate water, although some person-to-person spread was noted.

Untreated well water caused a large outbreak of gastrointestinal illness among attendees of two separate social events during a 2- day period at a rented reception hall. Consumption of water or iced tea (made with ice from same faucet) were the only risk factors associated with illness. Well water was positive for fecal coliforms, indicating that it was subject to contamination. Stool samples from seven of the 17 ill attendees tested were positive for norovirus.

Visitors to a snowmobile lodge experienced gastrointestinal illness during a 2-month period, resulting in one hospitalization. Closure of the lodge stopped the outbreak. Illness was associated only with consumption of water in the lodge, and stool samples from eight (61.5%) of 13 ill persons tested positive for norovirus by PCR. The lodge was served by three wells, which were all located in proximity to a septic tank or outhouse. Water samples also tested positive for norovirus by PCR and contained fecal coliforms. The wells were drilled in fractured granite, and sandy, porous soil existed above this. The cause of the outbreak was attributed to increased sewage load (which the septic tanks were unable to accommodate) combined with the geologic conditions in which the wells resided, which allowed rapid water percolation and thus decreased filtering. This outbreak and the following one also highlight the usefulness of PCR in detecting limited numbers of norovirus in water samples, because substantial volumes can be concentrated and tested in this manner. ( **Source:** Anderson AD,Haryford AG, Sarisky JP, et al. A waterborne outbreak of Norwalklike virus among snowmobilers—Wyoming, 2001. J Infect Dis 2003;187:303–6.)**Vol. 53 / SS-8 Surveillance Summaries 43**

**State in which Suspected Number**  **Outbreak outbreak or confirmed of persons date occurred etiologic agent affected Case description** 

**Chemicals**

**Unidentified etiologic aggents** September 2001

August 2001

September 2001

September 2001

November 2001

September 2001

June 2001 Wyoming

Florida

Florida

Minnesota

Minnesota

Ohio

Pennsylvania Norovirus

Ethylene glycol

Ethyl benzene, toluene, xylene

Copper and other minerals

Copper

Copper

AGI ¶ 83

3

2

4

28

2

19

* Occurred during 1999–2000 reporting period (previously unreported). † Occupational exposure. § Ornamental fountain exposure. ¶ Acute gastrointestinal illness of unknown etiology. Patrons of a bar experienced gastrointestinal illness, which was significantly associated only with consumption of water or ice from the bar. Stool samples from three ill persons tested positive for norovirus by PCR. The bar was served by a well, and water samples also tested positive for norovirus and contained fecal coliforms. The wells were drilled in fractured basalt and had perforations in the screens that covered the well casing. The cause of the outbreak was attributed to the close location of the well to aseptic tank and septic tank leach field combined with the underlying geologic conditions. In addition, a pellet chlorinator installed on the wellhead failed because of pellet dust blockage of the drop hole. ( **Source:** Parshionikar SU, Willian-True S, Fout GS, et al. Waterborne outbreak of gastroenteritis associated with a norovirus. Appl Environ Microbiol 2003;69:5263–8.)

The water supply at a middle school became contaminated byethylene glycol when a maintenance worker created a crossconnection between the air conditioning unit and the potable water supply. The worker used the potable water system to dilute the ethylene glycol solution in the chiller unit. The higher water pressure in the chiller unit forced the diluted ethylene glycol into the school’s water supply. Shortly thereafter, pink-colored water was noted in school bathrooms. Three students became ill with gastrointestinal symptoms as a result.

Bottled water purchased at a retail store caused gastrointestinal illness in two persons who consumed it. The water smelled like gasoline, and testing of sealed bottles revealed low levels of ethyl benzene, toluene, and xylene.

Children who consumed a soft drink consisting of well water and powdered drink mix at a church experienced gastrointestinal symptoms minutes later. Testing of the water revealed extremely high levels of copper and high levels of lead and zinc. Aluminum, antimony, arsenic, cadmium, and thallium were also detected. Investigation revealed that the well pump and pressure tank had been replaced 9 days before the outbreak. A high level of calcium hypochlorite (chlorine) was added to disinfect the system after this work. The system was then flushed, but the flushing did not include the line to the faucet that was used to make the drink. The high chlorine levels probably resulted in the leaching of metals from the interior of the water pipes and plumbing.

Children experienced gastrointestinal symptoms within minutes of drinking water at their elementary school. Water samples were identified as having extremely high levels of copper, and patientsreported the water appeared blue. An improperly installed antiscaling device was thought to be responsible.

Workers at a steel plant experienced gastrointestinal symptoms within minutes of consuming water from a drinking fountain at the plant. The water contained blue-green sediment, and had high levels of copper upon laboratory testing. A copper pipe had been bumped, causing a kink, and this was replaced 1 day before the outbreak. Copper-containing sediment dislodged from this pipe was believed to be the cause of the outbreak.

Illness was significantly associated with drinking water from one of four wells at a church camp. Water from this well was found to have no chlorine residual when tested in response to the outbreak.**44 MMWR October 22, 2004** 

# Glossary

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.
aquifer An underground bed or layer of earth, gravel, or porous stone that yields water.
boil-water advisory A statement to the public advising that tap water must be boiled before drinking it.

class Waterborne-disease outbreaks are classified according to the strength of the epidemiologic and water-quality data implicating water as the source of the outbreak (see Table 2).

coliforms All aerobic and facultative anaerobic, gram-negative, nonspore-forming, rod-shaped bacteria that ferment lactose with gas formation <48 hours at 95 o 

### F (35 o 

### C).

community water system A public water system that serves year-round residents of a community, subdivision, or mobile home park that has >15 service connections or an average of >25 residents for >60 days/year.

cross-connection Any actual or potential connection between a drinking water supply and a possible source of contamination or pollution (e.g., a wastewater line).
disinfection by-products Chemicals formed in water through reactions between organic matter and disinfectants.
distribution system Water pipes, storage reservoirs, tanks, and other means used to deliver drinking water to consumers or store it before delivery.
equalization basin A holding basin in which variations in flow and composition of a liquid stream are averaged, allowing storage and controlled release of wastewater to treatment processes.

fecal coliforms Coliforms that grow and produce gas at 112.1 o 

### F (44.5 o 

### C) in <24 hours.

filter backwash Water containing the material obtained by reversing the flow of water through a filter to dislodge the particles that have been retained on it.

filtration The process of removing suspended particles from water by passing it through one or more permeable membranes or media of limited diameter (e.g., sand, anthracite, or diatomaceous earth).

finished water The water (e.g., drinking water) delivered to the distribution system after treatment, if any.

free, residual chlorine level The concentration of chlorine in water that is not combined with other constituents, thus serving as an effective disinfectant.
groundwater system A system that uses water extracted from the ground (i.e., a well or spring).
groundwater under the Any water beneath the surface of the ground with substantial occurrence of insects or direct

influence of surface water other macrooganisms, algae, or large-diameter pathogens (e.g., Giardia intestinalisor 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.

hydrogeology The branch of geology that deals with the occurrence, distribution, and effect of ground water.**Vol. 53 / SS-8 Surveillance Summaries 45**



### Individual (or private) A water system that is not owned or operated by a water utility and that serves <15

water system residences or farms not having access to a public water system.

interactive fountain A fountain intended for (or accessible to) recreational use, often located at waterparks. In contrast, noninteractive (ornamental) fountains are intended for public display rather than recreational use and are often located in front of buildings and monuments.

maximum contaminant level The maximum permissible concentration (i.e., level) of a contaminant in water supplied to any user of a public water system.

noncommunity water system A public water system that 1) serves an institution, industry, camp, park, hotel, or business that is used by the public for >60 days/year but not year-round; 2) has >15 service connections or serves an average of >25 persons; and 3) is not a community water system.

nontransient noncommunity Public water system that serves >25 of the same persons for >6 months/year (e.g., a factory or

water system school) but not year-round.

norovirus A group of related, single-stranded RNA, nonenveloped viruses (genus Norovirus, family Caliciviridae ) that cause acute gastroenteritis in humans. Norovirus was recently approved as the official genus name for the group of viruses provisionally described as Norwalk-like viruses.
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.

raw water Surface water or groundwater that has not been treated in any way.

reverse osmosis A filtration process that removes dissolved salts and metallic ions from water by forcing it through a semipermeable membrane. This process is also highly effective in removing microbes from water.

source water Untreated water (i.e., raw water) used to produce drinking water.

surface water The water in lakes, rivers, reservoirs, and oceans.

total coliforms Nonfecal and fecal coliforms that are detected by using a standard test.

transient noncommunity Public water system that provides water to places where persons do not remain for long periods

water system of time (e.g., restaurants, highway rest stations, or parks with their own public water systems).
turbidity The quality (e.g., of water) of having suspended matter (e.g., clay, silt, or plankton) that results in loss of clarity or transparency.

untreated water Surface water or groundwater that has not been treated in any way (also called raw water).
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. Thebest indicator is one whose density or concentration correlates best with health hazards associated with a type of hazard or pollution.

watershed An area from which water drains to a single point; in a natural basin, the area contributing flow (i.e., water) to a place or point on a stream.
watershed-control program A program to protect a watershed from contamination or pollution.**MMWR**

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