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

department of health and human services

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: Centers 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.

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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

1Public Health Prevention Service, Epidemiology Program Office, CDC; 2Division of Parasitic Diseases, National Center for Infectious Diseases, CDC;

3Epidemic Intelligence Service, Epidemiology Program Office, CDC; 4Gunther F. Craun and Associates, Staunton, Virginia; 5Division of Healthcare Quality

and Promotion, National Center for Infectious Diseases, CDC; 6U.S. Environmental Protection Agency, Research Triangle Park, North Carolina

Abstract

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

Territorial Epidemiologists have 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 a

standard 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 collaboration

among local, state, federal, and international agencies on initiatives to prevent waterborne disease transmission. Data

obtained through this surveillance system are useful for identifying major deficiencies in the provision of safe recreational

water. Surveillance information can influence prevention recommendations and research priorities and lead to improved

water-quality regulations. However, the statistics reported in

this 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 occurring

or human-made contaminants. Standards for operating, disinfecting, and filtering public swimming and wading pools

are regulated by state and local health departments and, as a

result, 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 until

water 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 Beach

Watch 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 among

beachgoers. 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 water

or 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, a

private 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 case

counts 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 data

were excluded. Outbreaks of dermatitis, PAM, wound infections, or chemical poisonings are 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 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) includes

WBDOs 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 hospitalizations

and 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%) were

outbreaks 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 that tested 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) associated

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 pertaining 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). Cryptosporidium

species remained the most common cause of outbreaks associated with treated swimming water (50.0%), and toxigenic

E. coli serotypes 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 Cryptosporidium species 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 and

subsequently spread via infected swimmers to multiple community pools. At an Illinois waterpark (July 2001), 358 persons became ill with cryptosporidiosis after the introduction

of 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 among

persons 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, especially

by 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 park

visitors. Of the 44 persons with primary cases, 21 (49%) continued to use the beach and swim after illness onset. Although

the 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. Although

the 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 occasions

during 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 with

swimming 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 ill

with 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 children

became ill (Maine, November 2001) after playing in a large puddle, an activity

not usually associated with illness. The

puddle was caused by an overflowing

septic 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 to

norovirus (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 with

sediment from the lake or river bottom while diving or stirring up the soil (11).

Chemical. During 2001–2002, four outbreaks that affected

102 persons were attributed to chemical exposure in recreational water settings (Table 6). Two outbreaks that occurred

in 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 volatilize

into 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 avium complex and M. fortuitum.

Inadequate disinfection levels, lack of monitoring of pH and

disinfection levels, and having the spa inside the living area

were 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 improved

surveillance 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 1980 1984 1988 1992 1996 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

Cryptosporidium as 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 cause

contamination 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 WBDOs

reported 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,

Cryptosporidium accounted 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, Cryptosporidium accounted 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 (available 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 this

summary 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 public

swimming 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:H7

occurred 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., child

care 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 to

communitywide 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 an

intermediary 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 vigilance

regarding 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 outbreaks

occurred in beach areas that had substantial numbers of families bathing and swimming in the water. A common element

noted in these reports was the presence of diaper-aged children in the water, diaper changing on the beach, and washing

of 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 its

Beaches 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 of

minerals 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 hygiene

and 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). This

increase 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 collecting

stool 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 to

skin infections, spas have also been associated with ear infections (Pseudomonas), Pontiac fever/acute respiratory illness

(Legionella), and a previously unreported outbreak of Mycobacterium avium complex/M. fortuitum (15). The majority of

these reports noted inadequate disinfection of the water or

deficient maintenance. Because the higher temperatures commonly used in spas deplete disinfectant levels at a more rapid

rate, 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 tournaments

or 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 with

substantial 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 syndrome

is 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, swimmers

should 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 onshore

winds), 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 should

be 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 needed

on 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 of

these 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, they

might 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 public

about 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 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 public

health 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 the

local 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 rapid

detection of the etiologic agent and the source of water contamination. However, the course of an investigation reflects

the 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 cannot

always 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 investigate

WBDOs. CDC and EPA can be consulted regarding engineering and environmental aspects of recreational water treatment and collection of large-volume water samples to identify

pathogenic 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 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

• 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.

References

1. Craun GF, ed. Waterborne diseases in the United States. Boca Raton,

FL: CRC Press, Inc., 1986.

2. Lee SH, Levy DA, Craun GF, Beach MJ, Calderon RL. Surveillance for

waterborne-disease outbreaks—United States, 1999–2000. In: CDC

Surveillance Summaries, November 22, 2002. MMWR 2002;51(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. Surveillance for waterborne-disease outbreaks—United States, 1993–1994.

In: CDC Surveillance Summaries, April 12, 1996. MMWR 1996;45

(No. SS-1):1–33.

6. Moore AC, Herwaldt BL, Craun GF, Calderon RL, Highsmith AK,

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. Blackburn B, Craun GF, Yoder JS, et al. Surveillance for waterbornedisease outbreaks associated with drinking water—United States, 2001–

2002. In: Surveillance Summaries, October 22, 2004. MMWR

2004;53(No. SS-8):23–45.
Vol. 53 / SS-8 Surveillance Summaries 15

9. Environmental Protection Agency. Bacteriological ambient water quality criteria marine and fresh recreational waters. Cincinnati, OH:

National Service Center for Environmental Publications, 1986. EPA

publication no. 440584002.

10. CDC. Shigellosis outbreak associated with an unchlorinated fill-anddrain wading pool—Iowa, 2001. MMWR 2001;50:797–800.

11. CDC. Primary amebic meningoencephalitis—Georgia, 2002. MMWR

2003;52:962–4.

12. Massin N, Bohadana AB, Wild P, Héry M, Toamain JP, Hubert G.

Respiratory symptoms and bronchial responsiveness in lifeguards

exposed to nitrogen trichloride in indoor swimming pools. Occup

Environ Med 1998;55:258–63.

13. Gaginaire F, Axim S, Bonnet P, Hecht G, Hére M. Comparison of the

sensory irritation response in mice to chlorine and nitrogen trichloride. J Appl Toxicol 1994;14:405–9.

14. Emanuel BP. The relationship between pool water quality and ventilation. Environmental Health 1998;61:17–20.

15. Mangione EJ, Huitt G, Lenaway D, et al. Nontuberculous mycobacterial disease following hot tub exposure. Emerg Infect Dis

2001;7:1039–42.

16. Rickman OB, Ryu JH, Fidler ME, Kalra S. Hypersensitivity pneumonitis associated with Mycobacterium avium complex and hot tub

use. Mayo Clin Proc 2002;77:1233–7.

17. McNeal M. U.S. waterpark attendance breaks seventh straight record!

World Waterpark Association News, May 2000.

18. Guerrant RL. Cryptosporidiosis: an emerging highly infectious threat.

Emerg Infect Dis 1997;3:51–7.

19. Pruss A. Review of epidemiological studies on health effects from

exposure to recreational water. International J Epidemiol 1998;27:1–9.

20. Calderon RL, Mood EW, Dufour AP. Health effects of swimmers and

nonpoint sources of contaminated water. Int J Environ Health Res

1991;1:21–31.

21. CDC. Surveillance data from swimming pool inspections—selected

states and counties, United States, May–September 2002. MMWR

2003;52:513–6.

22. CDC. Swimming pools: safety and disease control through proper

design and operation. Atlanta, GA: US Department of Health and

Human Services, Public Health Service, CDC, 1976; DHHS publication no. (CDC) 88-8319.

23. CDC. “Norwalk-like viruses”: public health consequences and outbreak management. MMWR 2001;50(No. RR-9):1–18.

24. CDC. Surveillance data from public spa inspections—United States,

May–September 2002. MMWR 2004;53:553–5.

25. CDC. Suggested health and safety guidelines for public spas and hot

tubs. Atlanta, GA: US Department of Health and Human Services,

Public Health Service, CDC, 1981; DHHS publication no. (CDC)

99-960.

26. Verbrugge LM, Rainey JJ, Reimink RL, Blankespoor HD. Swimmer’s

itch: incidence and risk factors. Am J Pub Health 94:738–41.

27. CDC. Responding to fecal accidents in disinfected swimming venues.

MMWR 2001;50:416–7.
16 MMWR October 22, 2004

Appendix

Selected Case Descriptions of Outbreaks Associated with Recreational Water

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 in

which 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. He

had swum in a local river 9 days earlier. Environmental investigation revealed a high river temperature (91.4o

F [33oC]) 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. A

direct 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 located

on 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 the

swimming 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 95o

F (35oC).

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. parvum now 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 112.1o

F (44.5oC) 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 a

protective 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 tub or 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. The

best 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

1Division of Parasitic Diseases, National Center for Infectious Diseases, CDC; 2Epidemic Intelligence Service, Epidemiology Program Office, CDC ;

3Gunther F. Craun and Associates Staunton, Virginia; 4Public Health Prevention Service, Epidemiology Program Office, CDC; 5U.S. Environmental

Protection Agency, Research Triangle Park, North Carolina; 6Division 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 a

standard 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-Legionella bacteria. 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-quality

regulations. 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 is

attributable 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 occurred

during 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 collaboration

among local, state, federal, and international agencies on initiatives to prevent waterborne disease transmission. Data

obtained through this surveillance system are useful for identifying major deficiencies in providing safe drinking water.

Surveillance information can influence research priorities and

lead 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 estimates

available 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 tradeoffs

between 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

Cryptosporidium and additional treatment for filtered systems

on the basis of source-water concentrations; inactivation of

Cryptosporidium by 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 regulations

that 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 which

sources 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 must

establish 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 single

cases 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 or

serving 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), and

53,000 (32.9%) are community systems. Despite representing a minority of water systems, community systems serve

273 million persons (approximately 93.9% of the U.S. population) (31). Furthermore, a limited number of community

systems (3,900 [7.4%]) provide water to 81% of the community system population (31). Noncommunity, nontransient

systems 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 system

at 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 by

groundwater, 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); and

5: 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 III

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 of recreational water-associated outbreaks (8) includes

WBDOs 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, this

summary 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 primarily

for 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 outbreaks

during 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 of

persons 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 Legionella species, 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 of

these outbreaks, norovirus was suspected on the basis of symptoms and incubation period in an outbreak of gastrointestinal

illness 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 were

caused 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 intestinalis outbreaks, one

Cryptosporidium outbreak, 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 persons

were attributed to chemical contamination. Two were caused by high levels of

copper 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 by

ethyl 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 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 provide water

to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individual water systems are small

systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with 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.

† 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 water mains during construction or

repair, and contamination of a storage facility); and 5 = unknown or miscellaneous deficiency (e.g., contaminated bottled water or 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 deficiency 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 involving

infection 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, including

10 (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 the

only 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 provided

water-quality data. In four of these outbreaks, the contaminant that caused the outbreak was recovered directly from the

implicated water, including copper in two outbreaks (Minnesota, November 2001 and Ohio, September 2001), copper

and 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 provide water

to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individual water systems are small

systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with 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. †

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 water mains during construction or

repair, and contamination of a storage facility); and 5 = unknown or miscellaneous deficiency (e.g., contaminated bottled water or 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 summarize 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 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 provide water

to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individual water systems are small

systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with water not intended for drinking

(e.g., lakes, springs and creeks used by campers and boaters, irrigation water, and other non-potable sources with or without taps) are also classified as

individual systems. †

Examples of treatment deficiencies include temporary interruption of disinfection, chronically inadequate disinfection, or inadequate or no filtration; examples

of distribution system deficiencies include cross-connection, contamination of water mains during construction or repair, or contamination 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 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 provide water

to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individual water systems are small

systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with 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. †

Acute gastrointestinal illness of unknown etiology.
32 MMWR October 22, 2004

Water Systems and Water Sources

Because outbreaks caused by Legionella species 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 with

community 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 the

25 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 cases

of 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, untreated

groundwater; 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 Legionella species) outbreaks occurred in association with groundwater systems (all

were 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 inadequate or no filtration; examples

of distribution system deficiencies include cross-connection, contamination of water mains during construction or repair, or contamination 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 untreated

wells; 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 with

groundwater 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 Legionella species

Drinking Water Legionella Outbreaks

During 2001–2002, six Legionella outbreaks were related

to 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 (July

2002), 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 in

which 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 Legionella outbreak 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 a

mean 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 outbreaks

related 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 are

recognized 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, because

changes 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 health

departments). 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 are

those 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 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 provide water

to places in which persons do not remain for long periods of time (e.g., restaurants, highway rest stations, or parks). Individual water systems are small

systems not owned or operated by a water utility that serve <15 connections or <25 persons. Outbreaks associated with 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. †

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 water mains during construction or

repair, and contamination of a storage facility); and 5 = unknown or miscellaneous deficiency (e.g., contaminated bottled water or storage container).
Vol. 53 / SS-8 Surveillance Summaries 35

The identification of the etiologic agent of a WBDO

depends 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 waterborne

pathogens, 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 rarely

done. 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 and

water-quality concerns observed in outbreaks might not necessarily reflect or correspond with trends associated with

endemic waterborne illness. CDC and EPA have recently completed a series of epidemiologic studies designed to assess the

magnitude 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 Legionella

species, 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 Legionella species in the

respective distribution systems, and were most likely spread

by 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 >124o

F [return temperature]/>140oF [storage temperature] and cold water storage and distribution temperatures <68o

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 outbreaks

and because LD outbreaks have not been included in previous summaries, they will not be discussed in the following

sections, 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 was

attributable primarily to fewer community and noncommunity outbreaks. With institution and enforcement of better

regulations 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 and

reporting. 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 (seven

and 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 by

surface 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 2001

caused 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 reported

in 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 cartridge

filters. 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 point

of 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 help

by 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 influenced

by 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 even

if 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 the

wellhead, 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%) that

were 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 water

each 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 household

served 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 the

proposed 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 the

proportion 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 enhanced

surveillance 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 of

resources available to investigate these outbreaks, and the limited number of regulations that govern these systems. The

number and proportion of outbreaks attributed to individual

systems during 1999–2000 was at a 15-year high and accounted for much of the overall increase in the number of

outbreaks 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 to

assess 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 public

health 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 would

aide the detection and control of outbreaks. Routine reporting or sharing of water-quality data with the health department is recommended. Other means of improving surveillance

at 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 investigate

WBDOs. 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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11. Pontius FW. Implementing the 1996 SDWA amendments. JAWWA

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an automobile manufacturing plant. J Infect Dis 2003;187:1015–8.

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40 MMWR October 22, 2004

Appendix

Selected Case Descriptions of Outbreaks Associated with Drinking Water

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 surface

water. 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, and

69% 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 part

of 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 a

septic 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 by

ethylene 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 patients

reported 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 95o

F (35oC).

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 112.1o

F (44.5oC) 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 intestinalis or

Cryptosporidium) or substantial and relatively rapid shifts in water characteristics (e.g., turbidity, temperature, conductivity, or pH) that closely correlate with climatologic or surface water

conditions. Direct influence must be determined for individual sources in accordance with

criteria established by the state.

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. The

best 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.
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✩U.S. Government Printing Office: 2005-733-116/00043 Region IV ISSN: 1546-0738