Morbidity and Mortality Weekly Report

Surveillance Summaries November 22, 2002 / Vol. 51 / No. SS-8

Centers for Disease Control and Prevention

SAFER • HEAL SAFER • HEALTHIER • PEOPLETM

Surveillance for Waterborne-Disease

Outbreaks — United States, 1999–2000
MMWR

CONTENTS

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

Background ......................................................................... 2

EPA Regulations ................................................................ 2

Methods .............................................................................. 6

Data Sources .................................................................... 6

Definitions ........................................................................ 6

Outbreak Classification..................................................... 7

Results ................................................................................. 7

Outbreaks Associated with Drinking Water........................ 7

Outbreaks Associated with Recreational Water ................ 12

Outbreaks Associated with Occupational

Exposure to Water ....................................................... 17

Previously Unreported Outbreaks .................................... 17

Outbreaks Not Classified as WBDOs ............................... 18

Discussion ......................................................................... 18

Considerations Regarding Reported Results ..................... 18

Outbreaks Associated with Drinking Water...................... 20

Outbreaks Associated with Recreational Water ................ 23

Outbreaks Associated with Occupational

Exposures to Water ...................................................... 26

Conclusion ........................................................................ 26

Acknowledgments ............................................................. 27

References ......................................................................... 27

Appendix A........................................................................ 29

Appendix B ........................................................................ 37

Glossary ............................................................................ 45

SUGGESTED CITATION

General: Centers for Disease Control and Prevention.

Surveillance Summaries, November 22, 2002.

MMWR 2002:51(No. SS-8).

Specific: [Author(s)]. [Title of particular article]. In:

Surveillance Summaries, November 22, 2002.

MMWR 2002;51(No. SS-8):[inclusive page

numbers].

The MMWR series of publications is published by the

Epidemiology Program Office, 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

David W. Fleming, M.D.

Deputy Director for Science and Public Health

Dixie E. Snider, Jr., M.D., M.P.H.

Associate Director for Science

Epidemiology Program Office

Stephen B. Thacker, M.D., M.Sc.

Director

Division of Public Health Surveillance

and Informatics

Daniel M. Sosin, M.D., M.P.H.

Director

Associate Editor, Surveillance Summaries

Office of Scientific and Health Communications

John W. Ward, M.D.

Director

Editor, MMWR Series

Suzanne M. Hewitt, M.P.A.

Managing Editor

C. Kay Smith-Akin, M.Ed.

Project Editor

Lynda G. Cupell

Malbea A. Heilman

Beverly J. Holland

Visual Information Specialists

Quang M. Doan

Erica R. Shaver

Information Technology Specialists
Vol. 51 / SS-8 Surveillance Summaries 1

Surveillance for Waterborne-Disease Outbreaks —

United States, 1999–2000

Sherline H. Lee, M.P.H.1

Deborah A. Levy, Ph.D.1

Gunther F. Craun, M.P.H.2

Michael J. Beach, Ph.D.1

Rebecca L. Calderon, Ph.D.3

1Division of Parasitic Diseases

National Center for Infectious Diseases, CDC

2Gunther F. Craun and Associates

Staunton, Virginia 3U.S. Environmental Protection Agency

Research Triangle Park, North Carolina

Abstract

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

and Territorial Epidemiologists (CSTE) have maintained a collaborative surveillance system for the occurrences and

causes of waterborne-disease outbreaks (WBDOs).This surveillance system is the primary source of data concerning

the scope and effects of waterborne diseases on persons in the United States.

Reporting Period Covered: This summary includes data regarding outbreaks occurring during January 1999–December

2000 and previously unreported outbreaks occurring in 1995 and 1997.

Description of the System: The surveillance system includes data for outbreaks associated with drinking water and

recreational water. State, territorial, and local public health departments are primarily responsible for detecting and

investigating WBDOs and voluntarily reporting them to CDC on a standard form. 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 WBDO. First, >2 persons must have experienced a similar illness after either ingestion of drinking

water or exposure to water encountered in recreational or occupational settings. This criterion is waived for single cases

of laboratory-confirmed primary amebic meningoencephalitis and for single cases of chemical poisoning if waterquality data indicate contamination by the chemical. Second, epidemiologic evidence must implicate water as the probable source of the illness.

Results: During 1999–2000, a total of 39 outbreaks associated with drinking water was reported by 25 states. Included

among these 39 outbreaks was one outbreak that spanned 10 states. These 39 outbreaks caused illness among an

estimated 2,068 persons and were linked to two deaths. The microbe or chemical that caused the outbreak was identified for 22 (56.4%) of the 39 outbreaks; 20 of the 22 identified outbreaks were associated with pathogens, and two were

associated with chemical poisoning. Of the 17 outbreaks involving acute gastroenteritis of unknown etiology, one was

a suspected chemical poisoning, and the remaining 16 were suspected as having an infectious cause. Twenty-eight

(71.8%) of 39 outbreaks were linked to groundwater sources; 18 (64.3%) of these 28 groundwater outbreaks were

associated with private or noncommunity wells that were not regulated by EPA. Fifty-nine outbreaks from 23 states

were attributed to recreational water exposure and affected an estimated 2,093 persons. Thirty-six (61.0%) of the 59

were outbreaks involving gastroenteritis. The etiologic agent was identified in 30 (83.3%) of 36 outbreaks involving

gastroenteritis. Twenty-two (61.1%) of 36 gastroenteritis-related outbreaks were associated with pools or interactive

fountains. Four (6.8%) of the 59 recreational water outbreaks were attributed to single cases of primary amebic meningoencephalitis (PAM) caused by Naegleria fowleri. All four cases were fatal. Fifteen (25.4%) of the 59 outbreaks were

associated with dermatitis; 12 (80.0%) of 15 were associated with hot tubs or pools. In addition, recreational water

outbreaks of leptospirosis, Pontiac fever, and chemical keratitis, as well as two outbreaks of leptospirosis and Pontiac

fever associated with occupational exposure were also reported to CDC.

Interpretation: The proportion of drinking water outbreaks associated with surface water increased from 11.8%

during 1997–1998 to 17.9% in 1999–2000. The proportion of outbreaks (28) associated with groundwater sources

increased 87% from the previous reporting period (15 outbreaks), and these outbreaks were primarily associated (60.7%)
2 MMWR November 22, 2002

with consumption of untreated groundwater. Recreational water outbreaks involving gastroenteritis doubled (36 outbreaks) from the number of outbreaks reported in the previous reporting period (18 outbreaks). These outbreaks were

most frequently associated with Cryptosporidium parvum (68.2%) in treated water venues (e.g., swimming pools or

interactive fountains) and by Escherichia coli O157:H7 (21.4%) in freshwater venues. The increase in the number of

outbreaks probably reflects improved surveillance and reporting at the local and state level as well as a true increase in

the number of WBDOs.

Public Health Action: CDC and others have used surveillance data to identify the types of water systems, their

deficiencies, and the etiologic agents associated with outbreaks and evaluated current technologies for providing safe

drinking water and safe recreational water. Surveillance data are used also to establish research priorities, which can lead

to improved water-quality regulations. Only the groundwater systems under the influence of surface water are required

to disinfect their water supplies, but EPA is developing a groundwater rule that specifies when corrective action (including disinfection) is required. CDC and EPA are conducting epidemiologic studies to assess the level of waterborne

illness attributable to municipal drinking water in nonoutbreak conditions. Rules under development by EPA — the

Ground Water Rule (GWR), the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), and Stage 2

Disinfection Byproduct Rules (DBPR) — are expected to further protect the public from contaminants and disinfection byproducts in drinking water. Efforts by EPA under the Beaches Environmental Assessment, Closure, and Health

(BEACH) program are aimed at reducing the risks for infection attributed to ambient recreational water by strengthening beach standards and testing; providing faster laboratory test methods; predicting pollution; investing in health and

methods research; and improving public access to information regarding both the quality of the water at beaches and

information concerning health risks associated with swimming in polluted water. EPA’s Beach Watch (available at

http://www.epa.gov/waterscience/beaches) provides online information regarding water quality at U.S. beaches, local

protection programs, and other beach-related programs. CDC partnered with a consortium of local and national pool

associations to develop a series of health communication materials for the general public who attend treated recreational water venues and to staff who work at those venues. CDC has also developed a recreational water outbreak

investigation toolkit that can be used by public health professionals. All of the CDC materials are accessible at the CDC

Healthy Swimming website (http://www.cdc.gov/healthyswimming).

Introduction

During 1920–1970, statistical data regarding U.S. waterbornedisease outbreaks (WBDOs) were collected by multiple

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 (2–6). This surveillance

system includes data regarding outbreaks associated with

drinking water, recreational water, and other types of water

exposures. This report includes data for 1999 and 2000 and

for previously unreported drinking water-associated outbreaks

that occurred in 1995 and 1997.

CDC’s and EPA’s surveillance activities are intended to

1) characterize the epidemiology of WBDOs; 2) identify the

etiologic agents that caused WBDOs and determine why the

outbreaks occurred; 3) train public health personnel to detect

and investigate WBDOs; and 4) collaborate with local, state,

federal, and international agencies on initiatives to prevent

waterborne disease. Data obtained through this surveillance

system are useful for identifying major deficiencies in providing safe drinking water and recreational water. Surveillance

information can influence research priorities, lead to improved

water-quality regulations, and illustrate the burden of illness

attributed to water.

Background

EPA Regulations

Drinking Water

Public water systems are regulated under the Safe Drinking

Water Act (SDWA) of 1974 and its subsequent 1986 and

1996 amendments (7–9) (Box). Under SDWA, EPA is

authorized to set national standards to protect drinking water

and its sources against naturally occurring or man-made contaminants. The 1996 SDWA amendments require EPA to

publish a list every 5 years of contaminants that are known or

anticipated to occur in public water systems and that might

need to be regulated. The first list was called the drinking

water Contaminant Candidate List (CCL). CCL contained

60 contaminants/contaminant groups, included 10 pathogens,

and was published in the Federal Register on March 2, 1998

(10). A decision concerning whether to regulate >5 contaminants from CCL was required by August 2001. Microbial
Vol. 51 / SS-8 Surveillance Summaries 3

Safe Drinking Water Act/1974 and

1986 and 1996 amendments

Total Coliform Rule (TCR)/and

Maximum Contaminant Level

(MCL)/1989

Surface Water Treatment Rule

(SWTR)/1989

Information Collection Rule/

1996–1998

Interim Enhanced Surface Water

Treatment Rule (IESWTR)/1998

BOX. Environmental Protection Agency (EPA) regulations regarding drinking water, 1974–2003

Regulation/date Description

Authorizes EPA to set national standards to protect drinking water and its sources

Requires routine monitoring for total coliforms of all public water systems plus periodic

on-site inspections for systems that take <5 samples/month to evaluate and document treatment, storage, distribution network, operation and maintenance, and overall management.

Systems that collect >40 samples/month (i.e., typically, systems that serve >33,000 persons)

violate MCL if >5.0% of the samples collected during each month are positive for total coliforms;

systems that collect <40 samples/month violate MCL if two samples during the month are

positive for total coliforms. If a system has a total coliform-positive sample, then 1) that sample

must be tested for the presence of fecal coliforms or Escherichia coli, and 2) three repeat samples

must be collected (four, if the system collects <1 routine sample/month) within 24 hours and

analyzed for total coliforms. If positive, the sample must be analyzed for fecal coliforms or

Es. coli. In addition, >5 routine samples must be collected during the next month of sampling,

regardless of system size. For any size system, if two consecutive total coliform-positive samples

occur at one site during a month, and one of these samples is also fecal coliform-positive or

Es. coli-positive, the system has an acute violation of the Maximum Contaminant Level and

must notify the state and the public immediately.

Covers all water systems that use surface water or groundwater under the direct influence of

surface water; all systems must disinfect their water, and the majority of systems must filter

their water also, unless they meet EPA-specified filter-avoidance criteria that define highquality source water. Specific requirements include

• a combined filter-effluent–performance standard for turbidity (i.e., for rapid granular

filters, 0.5 nephelometric turbidity unit [NTU] maximum for 95% of measurements [taken

every 4 hours] during a month) and no single NTU reading >5.0;

• watershed protection, redundant disinfection capability, and other requirements for

unfiltered systems;

• a 0.2-mg/L disinfectant residual entering the distribution system; and

• maintenance of a detectable disinfectant residual in all parts of the distribution

system.

This rule requires that all such systems reduce the level of Giardia by 99.9% (3-log reduction)

and viruses by 99.99% (4-log reduction) through a combination of removal (filtration) and

inactivation (disinfection).

Requires systems serving >100,000 persons to provide treatment data and monitor disinfection byproducts and source water quality parameters. Surface water systems are also required

to monitor Cryptosporidium, Giardia, total culturable viruses, and total and fecal coliforms or

Es. coli >1 time/month for 18 months. Results provided information to facilitate development

of the Long Term 2 Enhanced SWTR, which is intended to protect against microbial risks by

targeting those systems with suboptimal quality source water and to balance the health risks

associated with disinfection byproducts and the anticipated Stage 2 Disinfection Byproduct Rule.

Follow-up to SWTR that covers all public systems using surface water or groundwater under

the direct influence of surface water and serving >10,000 persons. Key provisions include

• a 2-log Cryptosporidium-removal requirement for filtered systems;

• strengthened combined filter-effluent–turbidity performance standards for systems using

conventional filtration treatment or direct filtration (0.3 NTU maximum for 95% of

measurements during a month and no single NTU reading >1.0);

• individual filter turbidity monitoring provisions;
4 MMWR November 22, 2002

Lead and Copper Rule/2000

changes

Long Term 1 Enhanced SWTR

(LT1ESWTR)/2002 and the Filter

Backwash Recycling Rule (FBRR)/

2001

Long Term 2 Enhanced SWTR

(LT2ESWTR)/expected in 2003

Stage 2 Disinfection Byproduct

Rule (DBPR)/expected in 2003

Ground Water Rule (GWR) (1996

amendment to EPA’s Safe Drinking Water Act)/expected to be

finalized in 2003

• disinfection profile and benchmark provisions to ensure continued levels of microbial protection while facilities take necessary steps to comply with new disinfection byproduct standards;

• revision of the definition of groundwater under the influence of surface water and the

watershed-control requirements for unfiltered public water systems to include detection

of Cryptosporidium;

• requirements for covers on newly finished water reservoirs;

• sanitary surveys for all surface water systems regardless of size; and

• an MCL goal of zero oocysts for Cryptosporidium.

Streamlines requirements, promotes consistent national implementation, and reduces the

burden for water systems.

Companion regulations for IESWTR; LT1ESWTR applies to public water systems that use

surface water or groundwater under the direct influence of surface water and that serve <10,000

persons. FBRR regulates how treatment plants recycle water that has been used to backwash a

filter or that has been extracted from treatment plant sludge. FBRR regulates the point in the

treatment plant at which the contaminated recycle water may be introduced, assuring that the

water is subject to the entire particle and Cryptosporidium parvum removal process.

Applies to all systems using surface water or groundwater under the influence of surface water;

will provide additional protection against Cryptosporidium. Systems will be assigned to a treatment category on the basis of their source-water Cryptosporidium levels; the category then

determines how much additional treatment is required.

Will apply to community water systems and nontransient noncommunity water systems that

use an alternative to ultraviolet disinfection or deliver disinfected water; systems will be

required to monitor for total trihalomethanes and the sum of five haloacetic acids and comply

with MCLs at each monitoring location as a locational running annual average.

Applies to public groundwater systems (i.e., systems that have >15 service connections, or

regularly serve >25 persons daily for >60 days/year) or any system that mixes surface and

groundwater if the groundwater is added directly to the distribution system and provided to

consumers without treatment. Establishes multiple barriers to protect against bacteria and

viruses in drinking water from groundwater sources; establishes targeted strategy to identify

groundwater systems at high risk for fecal contamination. Key areas include

• system sanitary surveys;

• hydrogeologic sensitivity assessments for nondisinfected systems;

• source-water microbial monitoring by systems that do not disinfect and that draw from

hydrogeologically sensitive aquifers or have detected fecal indicators within the system’s

distribution system;

• corrective action by any system with substantial deficiencies or positive microbial samples

indicating fecal contamination; and

• compliance monitoring for systems that disinfect to ensure that they reliably achieve 4-log

(99.99%) inactivation or removal of viruses.

GWR does not apply to privately owned wells that serve <25 persons (e.g., individual homeowner wells).

BOX (Continued). Environmental Protection Agency (EPA) regulations regarding drinking water, 1974–2003

Regulation/date Description
Vol. 51 / SS-8 Surveillance Summaries 5

contamination is regulated under the Total Coliform Rule

(TCR) of 1989 and the Surface Water Treatment Rule

(SWTR) of 1989 (11–13). SWTR covers all water systems

that use surface water or groundwater under the direct influence of surface water (Glossary). SWTR is intended to protect against exposure to Giardia intestinalis, viruses, and

Legionella, as well as selected other pathogens. In 1998, EPA

promulgated the Interim Enhanced Surface Water Treatment

Rule (IESWTR) (14), which provides additional protection

against Cryptosporidium and other waterborne pathogens for

systems that serve >10,000 persons. In 2002, EPA finalized

the Long Term 1 Enhanced SWTR (LT1ESWTR) for public

water systems that use surface water or groundwater under

the direct influence of surface water and serve <10,000 persons (15). LT1ESWTR was proposed in combination with

the Filter Backwash Recycling Rule (FBRR), which was finalized in 2001 (16,17).

The 1996 Amendments require EPA to develop regulations

that require disinfection of groundwater systems as necessary

to protect the public health; EPA has proposed the Ground

Water Rule (GWR) to meet this mandate (18). GWR specifies the appropriate use of disinfection in groundwater and

addresses other components of groundwater systems to

ensure public health protection. GWR applies to public

groundwater systems (systems that have >15 service connections or regularly serve >25 persons/day for >60 days/year).

This rule also applies to any system that mixes surface and

groundwater if the groundwater is added directly to the distribution system and provided to consumers without treatment. GWR does not apply to privately owned wells.

Additional protection of groundwater from both chemical and

microbial contamination from shallow wells (including cesspools) is expected to be provided as a result of recent revisions

to the Underground Injection Control Regulations, published

December 7, 1999 (19).

To fill gaps in existing data regarding occurrence of microbial pathogens and other indicators of microbial contamination, occurrence of disinfection byproducts, and

characterization of treatment processes, EPA promulgated the

Information Collection Rule in 1996 (20), which required

systems serving >100,000 persons to provide treatment data

and monitor disinfection byproducts and source-water–quality

parameters. Surface water systems are also required to monitor for the presence of Cryptosporidium, Giardia, total

culturable viruses, and total* (Glossary) and fecal coliforms

or Escherichia coli >1 time/month for 18 months. The required

monitoring ended in December 1998, and data were analyzed.

EPA also made minor changes in 2000 to the Lead and

Copper Rule to streamline requirements, promote consistent

national implementation, and in certain cases, reduce the

burden for water systems. The action levels of 0.015 mg/L for

lead and 1.3 mg/L for copper remain the same (21).

Recreational Water

Regulation of recreational water is determined by state and

local governments. Standards for operating, disinfecting, and

filtering public swimming and wading pools are regulated by

state and local health departments and, as a result, are varied.

In 1986, EPA established a guideline for microbiological

water quality for recreational freshwater (e.g., lakes and ponds)

and marine water (22). The guideline recommends that the

monthly geometric mean concentration of organisms in freshwater should be <33/100 mL for enterococci or <126/100

mL for Es. coli. States have latitude regarding their guidelines

or regulations and can post warning signs to alert potential

bathers until water quality improves. Unlike treated venues

where disinfection can be used to address problems with

microbiological quality of the water, contaminated freshwater can require weeks or months to improve or return to normal. Prompt identification of potential sources of

contamination and remedial action is necessary to return bathing water to an appropriate quality for recreational use (23).

EPA’s Action Plan for Beaches and Recreational Waters

(Beach Watch) was developed as part of the Clean Water

Action Plan.† The intent of Beach Watch is to assist state,

tribal, and local authorities in strengthening and extending

programs that specifically protect users of recreational

waters. As part of the Beaches Act of 2000, the U.S. Congress

directed EPA to also develop a new set of guidelines for recreational water based on new water-quality indicators. Beginning in 2003, EPA will be conducting a series of epidemiologic

studies at recreational fresh and marine beaches in the United

States. These studies will be used to develop guidelines for

using the new water-quality indicators to be included in new

EPA guidelines.

Data collected as part of the national WBDO surveillance

system are used to describe the epidemiology of waterborne

diseases in the United States. Data 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 against

disease. Surveillance also enables identifying etiologic agents

* Total coliforms are considered indicator organisms that typically do not and environmental or behavioral risk factors that are

cause disease but might be associated with the presence of other diseasecausing organisms. Additional information regarding total coliforms is

available at http://www.epa.gov/safewater/dwa/electronic/tcr.pdf. † Additional information is available at http://www.cleanwater.gov.
6 MMWR November 22, 2002

responsible for these outbreaks. This information is used to

inform public health and regulatory agencies, water utilities,

pool operators, and other stakeholders of new or reemerging

trends that might necessitate different interventions and

changes in policies and resource allotment.

Methods

Data Sources

State, territorial, and local public health agencies have primary responsibility for detecting and investigating WBDOs,

and they voluntarily report them to CDC on a standard form

(CDC form 52.12, which is available at http://www.cdc.gov/

healthyswimming). The form solicits data related to 1) characteristics of the outbreak, including person, place, time, and

location of the outbreak; 2) results from epidemiological studies conducted; 3) specimen and water sample testing; and 4)

factors contributing to the outbreak, including environmental factors, water distribution, and disinfection concerns. Each

year, CDC requests reports from state and territorial epidemiologists or from persons designated as WBDO surveillance

coordinators. Additional information regarding water quality and treatment is obtained from the state’s drinking water

agency as needed. Numerical and text data are abstracted from

the outbreak form and supporting documents and are

entered into a database before 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

WBDO. First, >2 persons must have experienced a similar

illness after either ingestion of drinking water or exposure to

water encountered in recreational or occupational settings.

This criterion is waived for single cases of laboratoryconfirmed primary amebic meningoencephalitis and for single

cases of chemical poisoning if water-quality data indicate contamination by the chemical. Second, epidemiologic evidence

(Table 1) must implicate water as the probable source of the

illness. For drinking water, 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

WBDOs.

If primary cases (i.e., among persons exposed to contaminated water) and secondary cases (i.e., among persons who

became ill after contact with primary persons) 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 can be used if the population was sampled

randomly or the estimated count was calculated by applying

the attack rate to a standardized population.

Public water systems, which are classified as either community or noncommunity (Glossary), are regulated under SDWA.

Of the approximately 170,000 public water systems in the

United States, 113,000 (66.5 %) are noncommunity systems,

of which 93,000 are transient systems (i.e., public water systems that regularly serve >25 of the same persons for >6

months/year [e.g., highway rest stations, restaurants, and parks

with their own public water systems]) and 20,000 are

nontransient systems (Glossary). A total of 54,000 systems

(31.8%) are community systems. Community water systems

serve approximately 264 million persons in the United States

(96.0% of the U.S. population). Approximately 11 million

persons (4.0%) rely on private or individual water systems

(24,25) (Glossary). These statistics exclude outbreaks associated with these sources because they are not intended for drink- § Additional terms are defined in the glossary.

TABLE 1. Classification of investigations of waterborne-disease outbreaks — United States*

Class† Epidemiologic data Water-quality data

I Adequate§ Provided and adequate

Data were provided regarding exposed and unexposed persons, Historical information or laboratory data (e.g., the history that a

and the relative risk or odds ratio was >2 or the p-value was <0.05 chlorinator malfunctioned or a water main broke, no detectable freechlorine residual, or the presence of coliforms in the water)

II Adequate Not provided or inadequate (e.g., stating that a lake was crowded)

III Provided, but limited Provided and adequate

Epidemiologic data were provided that did not meet the criteria for

Class I, or the claim was made that ill persons had no exposures

in common besides water, but no data were provided

IV Provided, but limited Not provided or inadequate

* Outbreaks of Pseudomonas and other water-related dermatitis and single cases of primary amebic meningoencephalitis or of illness resulting from

chemical poisoning are not classified according to this scheme. †

On the basis of epidemiologic and water-quality data that were provided on CDC form 52.12. §

Adequate data were provided to implicate water as the source of the outbreak.
Vol. 51 / SS-8 Surveillance Summaries 7

ing and are not considered to be public water systems. Also

excluded from these statistics are the millions of persons who

use noncommunity systems while traveling or working.

In this surveillance system, 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 (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 one of the deficiencies in the following

list. If >1 deficiency is noted on the outbreak report form, the

deficiency that most likely caused the outbreak is noted.

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

(e.g., irrigation water tap).

Recreational waters include swimming pools, wading pools,

whirlpools, hot tubs, spas, water parks, interactive fountains, and

fresh and marine surface waters. Although the WBDO surveillance system includes whirlpool- and hot tub-associated outbreaks

of dermatitis caused by Pseudomonas aeruginosa, wound infections resulting from waterborne organisms are not included.

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 with 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 and single cases of

either primary amebic meningoencephalitis or illness resulting from chemical poisoning were 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 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 whether an investigation was optimally conducted. Likewise, a classification of

II, III, or IV should not be interpreted to mean that the

investigations were inadequate or incomplete. Outbreaks and

the resulting investigations occur under various 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, on the basis of

the relatively limited sample size available for analysis.

Results

Outbreaks Associated with Drinking Water

During 1999–2000, a total of 39 outbreaks associated with

drinking water were reported by 25 states (see Appendix A for

selected case descriptions). One of the 39 outbreaks was a

multistate outbreak of Salmonella Bareilly that included cases

from 10 states. Of the 39 total drinking water outbreaks, 15

outbreaks were reported for 1999 and 24 for 2000. Florida

reported the most outbreaks (15) during this period. These

39 outbreaks caused illness among an estimated 2,068

persons; 122 persons were hospitalized, and two died. The

median number of persons affected in an outbreak was 13.5

(range: 2–781). Outbreaks peaked during the summer months

(Figure 1), June–August.

FIGURE 1. Number of waterborne-disease outbreaks

associated with drinking water, by etiologic agent and month

— United States, 1999–2000 (n = 38)*

0

2

4

6

8

10

12

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

1999–2000

AGI†

Infectious

Chemical

Number of outbreaks

* One outbreak of Salmonella Bareilly was not included. †

Acute gastrointestinal illness of unknown etiology.
8 MMWR November 22, 2002

TABLE 2. Waterborne-disease outbreaks associated with drinking water — United States, 1999 (n = 15)*

Number Type of

State Month Class† Etiologic agent of cases system§ Deficiency¶ Source Setting

California Jul III AGI** 31 Ncom 2 Well Camp

Florida Jan III AGI 4 Com 2 Well Community

Florida Jan III Giardia intestinalis 2 Ind 2 Well Household

Florida Mar III AGI 6 Com 4 River/stream Apartment

Florida Mar III AGI 3 Com 4 Well Community

Florida May III AGI 3 Ind 2 Well Household

Florida Aug III AGI†† 4 Com 4 River/stream Apartment

Missouri Jun II Salmonella Typhimurium 124 Com 3 Well Community

New Jersey Nov IV Sodium hydroxide 2 Com 3 Well Community

New Mexico Jul I Small round-structured virus§§ 70 Ncom 3 Spring Camp

New York Aug I Escherichia coli O157:H7,

Campylobacter jejuni¶¶ 781 Ncom 2 Well Fairgrounds

Texas Nov I Es. coli O157:H7 22 Com 3 Well Community

Washington Jul II AGI 46 Ind 1 River/creek Household

Washington Aug I AGI 68 Ncom 2 Well Soccer match

Wisconsin Apr NA*** Nitrate 1 Ind 2 Well Household

* An outbreak is defined as 1) >2 persons experiencing a similar illness after ingestion of drinking water and 2) epidemiologic evidence that implicates

water as the probable source of the illness.

† On the basis of epidemiologic and water-quality data provided on CDC form 52.12.

§ Com = community; Ncom = noncommunity; Ind = individual; community and noncommunity water systems are public water systems that serve >15

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/year (e.g., factories or schools), whereas transient systems do not (e.g., restaurants, highway rest stations, or parks). Individual water systems are not owned or operated by a water utility and 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).

** Acute gastrointestinal illness of unknown etiology.

†† Unidentified chemical poisoning.

§§ Three persons had stool specimens that tested positive for small round-structured virus, and one person’s stool specimen tested positive for Ca. jejuni.

¶¶ A total of 126 persons had stool specimens that tested positive for Es. coli O157:H7; 43 persons had stool specimens that tested positive for Ca. jejuni.

One person’s stool specimen tested positive for both organisms.

*** Not applicable, see Table 1.

Nine of the 39 (23.1%) outbreaks were assigned to Class I

on the basis of epidemiologic and water-quality data; three

(7.7%) were Class II; 25 (64.1%) were Class III; and 1 was

Class IV (Table 1). One of two outbreaks associated with a

chemical etiology was not assigned a class because that

outbreak was a single case of illness resulting from nitrate

poisoning associated with consumption of water from a private well. Outbreaks are listed by state (Tables 2 and 3) and

are tabulated by the etiologic agent, the water system type

(Table 4), and by the type of deficiency and type of water

system type (Table 5).

Etiologic Agents

Twenty (51.3%) of the 39 outbreaks were of known infectious etiology; 17 (43.6%) were of unknown etiology; and

two (5.1%) were attributed to chemical poisoning. Of the

20 outbreaks with known infectious etiology, seven (35.0%)

were caused by parasites; nine (45.0%) were caused by

bacteria; and four (20.0%) were caused by viruses (Figure 2)

(Appendix A).

Parasites. Seven outbreaks affecting 57 persons were

attributed to parasitic infection: six Giardia outbreaks and

one Cryptosporidium outbreak. Six outbreaks of Giardia associated with drinking water affected 52 persons from five states:

Florida (two outbreaks), New Mexico (one), New Hampshire

(one), Minnesota (one), and Colorado (one). These outbreaks

occurred in January (one), June (one), July (one), August (one),

and September (two). Four outbreaks were associated with

well water systems, and two were associated with surface

water systems. Two outbreaks caused by G. intestinalis involved

possible contamination of wells by animal feces. G. intestinalis

can infect mammalian hosts, which in turn, can serve as reservoirs for human infection. Water treatment failure was a

factor in two other outbreaks of Giardia.

Bacteria. Nine outbreaks affecting an estimated 1,166 persons were attributed to bacterial infection: four Es. coli O157:

H7 outbreaks, one Campylobacter jejuni, one Salmonella

Typhimurium, one Sa. Bareilly, and two mixed Ca. jejuni and

shiga toxin-producing Es. coli (O157:H7 or O111) outbreaks.
Vol. 51 / SS-8 Surveillance Summaries 9

TABLE 3. Waterborne-disease outbreaks associated with drinking water — United States, 2000 (n = 24)*

Number Type of

State Month Class† Etiologic agent of cases system§ Deficiency¶ Source Setting

California Jul I Norwalk-like virus 147 Ncom 2 Well Camp

California Jul I Escherichia coli O157:H7 5 Ind 5 River/creek Camp

California Sep III AGI** 63 Ind 5 Irrigation system Football game

Colorado Aug III Giardia intestinalis 27 Ncom 3 River Resort

Florida Mar III AGI†† 19 Com 3 Well Trailer park

Florida Apr III AGI 21 Com 3 Well Trailer park

Florida Apr I AGI 71 Ind 2 Well Community

Florida Jun III AGI§§ 2 Ind 2 Well Household

Florida Jul III AGI 3 Ind 2 Well Household

Florida Jul III AGI 3 Ind 2 Well Household

Florida Aug III AGI 4 Ind 2 Well Household

Florida Sep III G. intestinalis 2 Ind 4 Well Household

Florida Dec III Cryptosporidium parvum 5 Com 4 Well Community

Idaho Apr III Es. coli O157:H7 4 Ind 5 Irrigation canal Household

Idaho Jun III Campylobacter jejuni 15 Ncom 2 Spring Camp

Idaho Jul III AGI 65 Ncom 2 Well Restaurant

Kansas Jun III Norwalk-like virus 86 Ncom 2 Well Reception hall

Minnesota Jun III G. intestinalis¶¶ 12 Ncom 2 Well Camp

New Hampshire Sep III G. intestinalis 5 Ind 3 Well Household

New Mexico Jul II G. intestinalis 4 Ind 5 River Rafting trip

Ohio Aug I Es. coli O157:H7 29 Com 4 Surface water*** Fairgrounds

Utah Aug III Ca. jejuni††† 102 Ind 5 Irrigation water Football camp

West Virginia Jun III Norwalk-like virus 123 Ncom 3 Wells Camp

Multistate Apr–Aug I Salmonella Bareilly 84 Ind 5§§§ Municipal/spring§§§ Wells/bottled water***

* An outbreak is defined as 1) >2 persons experiencing a similar illness after ingestion of drinking water and 2) epidemiologic evidence that implicates

water as the probable source of the illness.

† On the basis of epidemiologic and water-quality data provided on CDC form 52.12.

§ 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/year (e.g., factories or schools), whereas transient systems do not

(e.g., restaurants, highway rest stations, or parks). Individual water systems are not owned or operated by a water utility and 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).

** Acute gastrointestinal illness of unknown etiology.

†† Persons also reported rashes in addition to acute gastrointestinal illness.

§§ One person had a stool specimen that tested positive for Blastocystis hominis.

¶¶ Eight persons had stool specimens that tested positive for G. intestinalis; one stool specimen tested positive for Dientamoeba fragilis.

*** Type of water was not specified on report form.

††† Thirty-seven persons had stool specimens that tested positive for Ca. jejuni; four persons’ stool specimens tested positive for Es. coli O157:H7, and three

persons had stool that tested positive for Es. coli O111.

§§§ The outbreak implicated both drinking water from private wells and springs and water bottled by one facility. The bottling facility used two sources of water.

The two outbreaks with multiple pathogens caused the two

largest bacterial drinking water outbreaks reported during this

study period.

Viruses. During this period, four outbreaks involving viral

gastroenteritis were reported. A total of 426 persons reported

illness; no hospitalizations or deaths were reported in association with these four viral outbreaks. Three of the four outbreaks occurred in camp facilities in California, New Mexico,

and West Virginia. All three water sources were noncommunity

groundwater sources.

Chemicals. During 1999, two outbreaks involving chemical contamination were reported. A total of three persons were

affected by contamination of drinking water from nitrate and

sodium hydroxide.

Unidentified Etiologic Agents. Seventeen outbreaks

involving gastroenteritis of unknown etiology were reported

from four states, affecting an estimated 416 persons and

resulting in five hospitalizations. Testing for certain

enteric pathogens (including ova and parasite testing) was

attempted in five of the 17 outbreaks. In a June 2000

outbreak affecting 2 persons, stool specimens collected from

one person tested negative for G. intestinalis but positive for

Blastocystis hominis. However, whether B. hominis was the cause

of the reported illness is unclear, and the pathogenicity of
10 MMWR November 22, 2002

TABLE 4. Waterborne-disease outbreaks associated with drinking water, by etiologic agent and type of water system — United

States, 1999–2000 (n = 39)

Type of water system*

Community Noncommunity Individual Total

Etiologic agent Outbreaks Cases Outbreaks Cases Outbreaks Cases Outbreaks Cases

AGI† 6§ 57 3 164 8 195 17 416

Giardia intestinalis 0 0 2 39 4 13 6 52

Escherichia coli O157:H7 2 51 0029 4 60

Norwalk-like viruses (NLV) 0 0 3 356 0 0 3 356

Salmonella species¶ 1 124 0 0 1 84 2 208

Campylobacter jejuni 0 0 1 15 1 102 2 117

Es. coli O157:H7/Ca. jejuni 0 0 1 781 0 0 1 781

Small round-structured virus 0 0 1 70 0 0 1 70

Cryptosporidium parvum 150000 1 5

Sodium hydroxide 120000 1 2

Nitrate 000011 1 1

Total 11 239 11 1,425 17 404 39 2,068

Percentage 28.2 11.6 28.2 68.9 43.6 19.5 100.0 100.0

* 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/year (e.g., factories or schools), whereas transient systems do not (e.g., restaurants, highway rest stations, or parks). Individual water systems

are not owned or operated by a water utility and 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. §

One outbreak of four cases was caused by an unidentified chemical. ¶

One outbreak was serotype Typhimurium, and one outbreak was serotype Bareilly.

TABLE 5. Waterborne-disease outbreaks associated with drinking water, by type of deficiency and type of water system —

United States, 1999–2000 (n = 39)

Type of water system*

Community Noncommunity Individual Total

Type of deficiency† Outbreaks % Outbreaks % Outbreaks % Outbreaks %

Untreated surface water 0 0 0 0 1 5.9 1 2.6

Untreated groundwater 1 9.0 8 72.7 8 47.0 17 43.6

Inadequate treatment 5 45.5 3 27.3 1 5.9 9 23.1

Distribution system 5 45.5 0 0 1 5.9 6 15.4

Miscellaneous or unknown 0 0 0 0 6 35.3 6 15.4

Total 11 100.0 11 100.0 17 100.0 39 100.0

* 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/year (e.g., factories or schools), whereas transient systems do not (e.g., restaurants, highway rest stations, or parks). Individual water systems

are not owned or operated by a water utility and 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. †

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 deficiencies include contaminated bottled water.

B. hominis has been debated in the scientific community (26).

Stool specimens were negative for parasitic and bacterial

enteric pathogens in two outbreaks in Washington (July 1999

and August 1999) and in two Florida outbreaks (March 1999

and April 2000) (Appendix A).

In addition, suspected pathogens were noted in four other

outbreak reports submitted. On the basis of symptoms of illness, Norwalk-like virus (NLV) was suspected in an Idaho

outbreak among firefighters that caused 65 illnesses and four

hospitalizations, but the outbreak was not laboratoryconfirmed. G. intestinalis was suspected in an April 2000 outbreak in a Florida trailer park affecting 21 persons, on the

basis of the incubation period and symptoms reported. In

another outbreak in a Florida trailer park in March 2000

among 19 persons, a bacterial pathogen was suspected as the

cause of the outbreak on the basis of the symptoms, which

included conjunctivitis and dermatitis in addition to gastroenteritis. A chemical agent was suspected as the cause of illness among four residents in a Florida apartment building

who had a cross-connection between their drinking water and
Vol. 51 / SS-8 Surveillance Summaries 11

a toilet flush-valve. The residents of the apartment had noted

blue tap water before onset of illness on multiple occasions

before an improper flush valve in the toilet tank was discovered.

Four outbreaks of gastroenteritis were associated with consumption of untreated water from private wells. These four

outbreaks occurred in Florida and affected 3–4 persons each.

In July 2000, flooding was a possible contributor to two outbreaks. Water in each of the homes tested positive for coliforms

and did not have adequate disinfection.

Water-Quality Data

Water-quality data (i.e., information regarding the presence

of coliform bacteria, pathogens, or chemical contaminants)

were available for 35 (89.7%) of the 39 drinking water outbreaks. Two reports of outbreaks of confirmed or suspected

infectious etiology and two reports of outbreaks of confirmed

or suspected chemical etiology did not provide water-quality

data.

Of the 36 reports of outbreaks with a suspected or confirmed infectious etiology, 33 outbreaks provided water-quality

data. Twenty-six (78.8%) of the 33 outbreaks with a suspected

or confirmed infectious etiology reported a positive coliform,

total coliform, or fecal coliform result. Organisms also were

detected in the water in two of these outbreaks. In August

2000, Ca. jejuni was detected in the water in a mixed

Ca. jejuni/Es. coli O157:H7 outbreak in Utah, although shiga

toxins were not detected. Es. coli

O157:H7 was found in the water in

a July 2000 California outbreak. In

a 2000 Colorado outbreak, the presence of G. intestinalis was demonstrated in a sample from the water

holding tank, despite the lack of

coliform data.

Of the three outbreaks with either

a confirmed or suspected chemical

etiology, only one demonstrated that

the chemical had been directly in the

water. Tap water was tested after the

health department was notified that

an infant had methemoglobinemia.

Both fecal coliforms and 28 mg/L

of nitrate were detected in the

water. For an outbreak where burns

and gastroenteritis were reported

and linked to a sodium hydroxide

spill, a pH test of the water that

could indicate whether NaOH or

another basic substance had spilled

into the water was not documented.

However, the environmental assessment indicated the tank

contents had emptied into the water. A third suspected chemical outbreak involving a cross-connection between a toilet

flush-valve and the drinking water system did not have waterquality data available.

In 11 of the 35 outbreaks, water was not sampled for

coliforms until >1 month after the first case associated with

the outbreak was reported (range: 5–16 weeks). In four of

these 11 outbreaks, the water samples did not test positive for

coliforms (fecal or total), chemicals, or pathogens. Instead,

these were confirmed as outbreaks by epidemiologic data or

by reports that treatment deficiencies had occurred.

Water Systems and Water Sources

Eleven (28.2%) of the 39 drinking water outbreaks were

associated with community systems, 11 (28.2%) with noncommunity systems, and 17 (43.6%) with individual water

systems (Tables 4 and 5). Ten (25.6%) of the 39 drinking

water outbreaks were associated with surface water, including

three outbreaks that implicated irrigation water not intended

for consumption. Twenty-nine (74.4%) of the 39 drinking

water outbreaks, including the outbreak associated with

bottled water, were associated with groundwater sources (wells

and springs).

Five (45.5%) of the 11 outbreaks associated with community water systems were caused by treatment deficiencies; one

Unidentified

43.6%

Bacterial

23.1%

Chemical

5.1%

Parasitic

17.9%

Community

28.2%

Individual

43.6%

Noncommunity

28.2%

Well

68.4%

Irrigation system

7.9%

Surface water

18.4%

Treatment

deficiency

23.1%

Untreated

groundwater

43.6%

Distribution system

15.4%

Spring

5.3%

Miscellaneous

15.4%

Viral

10.3%

Untreated surface

water 2.6%

Etiologic agent (n = 39) Water system (n = 39)

Water source (n = 38)* Deficiency (n = 39)

FIGURE 2. Waterborne-disease outbreaks associated with drinking water, by etiologic agent,

water system, water source, and deficiency — United States, 1999–2000 (n = 39)

* One outbreak of Salmonella Bareilly was not included.
12 MMWR November 22, 2002

(9.0%) outbreak was related to contaminated, untreated

groundwater, and five (45.5%) outbreaks were related to

problems in the water distribution system. Two of the five

distribution system problems were related to cross-connections

between the distribution system and an irrigation well. The

third outbreak related to a community water source had a

household cross-connection between the toilet water and main

kitchen tap. One outbreak of Cr. parvum (Florida, December

2000) was related to a repeated history of water main breaks.

In another outbreak in Ohio in August 2000, deficiencies in

the distribution system of a fairgrounds might have allowed

back-siphonage of animal manure into the water used by food

and beverage vendors.

Ten (90.1%) of 11 outbreaks associated with noncommunity water systems occurred in groundwater systems. Seven of

the 10 groundwater outbreaks were linked to untreated wells,

and one of the 10 involved consumption of untreated spring

water. Two of the 10 outbreaks were related to treatment

deficiencies in water taken from wells or a spring and

were associated with outbreaks of NLV and a small roundstructured virus. An outbreak associated with G. intestinalis

related to consumption of surface water occurred when a pump

failure and a defective filter cartridge resulted in river water

entering the drinking water holding tank without filtration.

No information concerning chlorine levels from water samples

was provided.

Nine (52.9%) of 17 outbreaks associated with individual

water systems occurred in groundwater systems. Eight of these

groundwater systems were wells that were not treated routinely; one outbreak of giardiasis occurred when the filtration

system for a well was inadvertently turned off. Five (31.3%)

TABLE 6. Waterborne-disease outbreaks of gastroenteritis associated with recreational water — United States, 1999 (n = 15)

Number

State Month Class* Etiologic agent Illness of cases Source Setting

California Jun III AGI† Gastroenteritis 23 Pool Apartment complex

Connecticut Jul II Escherichia coli O121:H19 Gastroenteritis 11 Lake Lake

Florida Mar III Campylobacter jejuni Gastroenteritis 6 Pool Private home

Florida Aug I Shigella sonnei, Interactive

Cryptosporidium parvum§ Gastroenteritis 38 fountain Beach park

Florida Aug IV Cr. parvum Gastroenteritis 6 Pool Private home

Florida Sep III Es. coli O157:H7 Gastroenteritis 2 Ditch water Community

Idaho Jun IV Norwalk-like virus Gastroenteritis 25 Hot springs Resort

Illinois Jun III AGI Gastroenteritis 25 Lake Lake

Massachusetts Jul III Giardia intestinalis Gastroenteritis 18 Pond Pond

Minnesota Jul III Cr. parvum Gastroenteritis 10 Pool Trailer park

Nebraska Jun IV Es. coli O157:H7 Gastroenteritis 7 Wading pool Child care center

New York Jun II Norwalk-like virus Gastroenteritis 168 Lake County park

Washington Aug I Es. coli O157:H7 Gastroenteritis 36 Lake State park

Wisconsin Jul IV Cr. parvum Gastroenteritis 10 Pool Municipal pool

Wisconsin Aug II Es. coli O157:H7 Gastroenteritis 5 Lake/pond Swimming beach

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12. †

Acute gastrointestinal illness of unknown etiology. §

Five persons had stool specimens that tested positive for Shigella sonnei; two stools tested positive for Cryptosporidium parvum.

of the 16 outbreaks occurred when persons drank water not

intended for direct consumption from irrigation systems or

when they consumed surface water that had been ineffectively

or improperly treated. One (6.3%) of the 16 outbreaks in a

system occurred in a home where creek water on the property

was directly consumed without treatment.

Of the nine bacterial outbreaks, four occurred in groundwater systems (one was associated with a deficiency in the

distribution system, one with a treatment deficiency, and two

occurred in untreated systems). Six of seven parasitic outbreaks

occurred in groundwater systems: three occurred in untreated

systems; two involved problems in the distribution system;

and one was related to a treatment deficiency. All four viral

outbreaks occurred in noncommunity groundwater systems.

Two occurred in untreated wells, and two were related to treatment deficiencies in a spring and well. Two chemical outbreaks were related to treatment deficiencies in well water.

Fourteen of the 17 outbreaks of unknown etiology were linked

to groundwater systems. Ten of these 14 outbreaks occurred

in untreated systems; two were related to distribution system

problems, and two were related to treatment deficiencies.

Outbreaks Associated

with Recreational Water

During 1999–2000, a total of 23 states reported 59 outbreaks associated with recreational water (Tables 6–9)

(see Appendix B for selected case descriptions). Twenty-three

outbreaks were reported for 1999, and 36 for 2000. The states

that reported the largest number of outbreaks were Florida

(14 outbreaks) and Minnesota (eight outbreaks). These
Vol. 51 / SS-8 Surveillance Summaries 13

TABLE 7. Waterborne-disease outbreaks of gastroenteritis associated with recreational water — United States, 2000 (n = 21)

Number

State Month Class* Etiologic agent Illness of cases Source Setting

Colorado Aug I Cryptosporidium parvum Gastroenteritis 112 Pool Municipal pool

Florida May IV AGI† Gastroenteritis 2 Lake Lake

Florida Jul III AGI Gastroenteritis 4 Outdoor spring County park

Florida Jul III Cr. parvum Gastroenteritis 3 Pool Apartment complex

Florida Aug III Cr. parvum Gastroenteritis 5 Pool Country club

Florida Aug I Cr. parvum Gastroenteritis 19 Pool Resort

Florida Aug III AGI Gastroenteritis 9 Pool Motel

Florida Aug III Cr. parvum Gastroenteritis 5 Pool Condominium

Georgia Jun II Cr. parvum Gastroenteritis 36 Pools§ Community

Maine Jul II AGI Gastroenteritis 32 Lake/pond Swimming beach

Minnesota Jul II Cr. parvum¶ Gastroenteritis 220 Lake Swimming beach

Minnesota Jul IV Shigella sonnei** Gastroenteritis 15 Lake/pond Swimming beach

Minnesota Jul III Cr. parvum Gastroenteritis 7 Pool Day camp

Minnesota Jul II Cr. parvum Gastroenteritis 6 Pool Hotel

Minnesota Aug II Sh. sonnei Gastroenteritis 25 Lake Public beach

Minnesota Aug IV Cr. parvum Gastroenteritis 4 Pool Municipal pool

Missouri Sep III Shigella flexneri Gastroenteritis 6 Wading pool Community

Nebraska Jun I Cr. parvum Gastroenteritis 225 Pools Community

Ohio Jun I Cr. parvum Gastroenteritis 700 Pool Private swim club

South Carolina Jul IV Cr. parvum Gastroenteritis 26 Pool Community

Wisconsin Jan IV Norwalk-like virus Gastroenteritis 9 Pool Motel

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12.

† Acute gastrointestinal illness of unknown etiology.

§ Persons swam in a community pool and an inflatable pool.

¶ Seventeen persons had stool specimens that tested positive for Cr. parvum. One person had a stool specimen that tested positive for Giardia intestinalis.

One person had a stool specimen that tested positive for both organisms.

** Fourteen of 15 stool specimens tested positive for Shigella; one person tested positive for Cr. parvum; and one tested positive for both.

TABLE 8. Waterborne-disease outbreaks of meningoencephalitis, keratitis, leptospirosis, and Pontiac fever associated with

recreational water — United States, 1999–2000 (n = 8)

Number

State Year Month Class* Etiologic agent Illness of cases Source Setting

California 2000 Apr NA† Naegleria fowleri Meningoencephalitis 1 Mudhole Mudhole

Florida 1999 Oct NA N. fowleri Meningoencephalitis 1 Pond Pond

Florida 2000 —§ NA N. fowleri Meningoencephalitis 1 — —

Guam 2000 Jul II Leptospira interrogans Leptospirosis 21 Lake Adventure race

Vermont 2000 Feb NA Bromine Chemical keratitis 3 Pool Pool

Texas 1999 Sep II Unknown¶ Acute respiratory infection 12 Hot tub Ranch

Texas 2000 Jul NA N. fowleri Meningoencephalitis 1 Lake Lake

Wisconsin 2000 May I Legionella pneumophila Pontiac fever 20 Whirlpool Motel

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12. †

Not applicable. §

The month the outbreak occurred was not reported; the source and setting were not reported. ¶

Clinical specimens tested negative for Legionella pneumophila serotypes 1 and 6, adenovirus, influenza virus, and parainfluenza virus.

59 outbreaks affected 2,093 persons and resulted in 25 hospitalizations and four deaths. The median size of the outbreak

was 10 persons (range: 1–700).

Of the 59 outbreaks, 36 were outbreaks of gastroenteritis

(Tables 6 and 7); 15 were outbreaks of dermatitis (Table 9);

four were cases of meningoencephalitis; and the remaining

four outbreaks were of leptospirosis, chemical keratitis, acute

respiratory infection of unknown etiology, and Pontiac fever

(Table 8). Thirty-one (86.1%) of the 36 outbreaks involving

gastroenteritis occurred during the summer months (i.e., June–

August) (Figure 3). Outbreaks of dermatitis associated with

recreational water contact were reported more frequently in

February, March, June, and July. The four cases of primary

amebic meningoencephalitis occurred in the warmer months

(April–October).

Etiologic Agents

Of the 59 recreational water outbreaks, 44 (74.6%) were of

known infectious etiology (Tables 6–9). Of the 36 outbreaks

involving gastroenteritis, 17 (47.2%) were caused by parasites; nine (25.0%) by bacteria; three (8.3%) by viruses; one

(2.8%) by a combination of parasites and bacteria; and the

remaining six (16.7%) were of unknown etiology (Figure 4).
14 MMWR November 22, 2002

FIGURE 3. Number of waterborne-disease outbreaks

associated with recreational water, by illness and month —

United States, 1999–2000 (n = 58)*

0

2

4

6

8

10

12

14

16

18

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

1999–2000

Other

Meningoencephalitis

Dermatitis

Gastroenteritis

Number of outbreaks

* Information regarding the month was not provided for one outbreak of

meningoencephalitis.

TABLE 9. Waterborne-disease outbreaks of dermatitis associated with recreational water — United States, 1999–2000 (n = 15)

Number

State Year Month Class* Etiologic agent of cases Source Setting

Alaska 2000 Oct NA† Pseudomonas aeruginosa§ 29 Pool/hot tub Hotel

Arkansas 1999 Jun NA P. aeruginosa§ 10 Pool Community

Arkansas 2000 Feb NA P. aeruginosa§ 26 Pool/ hot tub Motel

California 2000 Jun IV Schistosomes** 6 Pond Pond

California 2000 Jul IV Schistosomes** 4 Pond Pond

Colorado 1999 Feb NA P. aeruginosa¶§ 19 Hot tub Hotel

Colorado 1999 Dec NA P. aeruginosa†† 5 Hot tub Ski lodge

Florida 2000 Aug NA P. aeruginosa†† 6 Hot tub Apartment complex

Maine 2000 Feb NA P. aeruginosa¶ 9 Hot tub/pool Hotel

Maine 2000 Mar NA P. aeruginosa§ 11 Hot tub Hotel

Minnesota 2000 Dec NA P. aeruginosa¶ 16 Hot tub Private

Oregon 1999 Jul IV Schistosomes** 2 Lake Lake

Vermont 1999 Jun NA P. aeruginosa†† 9 Hot tub Hotel

Vermont 1999 Feb NA P. aeruginosa†† 11 Hot tub Vacation home

Washington 2000 Mar NA P. aeruginosa†† 10 Pool/hot tub Motel

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12.

† Not applicable.

§ Organism isolated from water.

¶ Laboratory-confirmed case.

** Suspected etiology on the basis of clinical syndrome and setting.

†† Suspected etiology on the basis of clinical syndrome.

Of the 23 nongastroenteritis-related recreational outbreaks,

seven were attributed to P. aeruginosa, four to free-living amoebae, one to Leptospira species, one to Legionella species, and

one to bromine (Tables 8 and 9). Nine nongastroenteritisrelated recreational outbreaks were of unknown etiology, eight

of which were suspected but not confirmed to be caused by

P. aeruginosa or schistosomes. The ninth outbreak of unknown

etiology was suspected to be caused by a virus or by Legionella

pneumophila on the basis of observed symptoms and the epidemiologically implicated vehicle of transmission. Of the 59

recreational water outbreaks, 21 (35.6%) were associated with

fresh or surface water, and 37 (62.7%) with treated (e.g., chlorinated) water. Information regarding the water venue for an

outbreak of meningoencephalitis was not provided.

Parasites. Sixteen of the 17 parasitic recreational water outbreaks involving gastroenteritis were caused by Cr. parvum.

The seventeenth outbreak was caused by G. intestinalis.

Fifteen of the 17 parasitic outbreaks occurred in chlorinated

venues; in these outbreaks, inadequate treatment, disrupted

chlorine disinfection, or suboptimal pool maintenance were

contributing factors to the outbreaks. Cr. parvum is highly

resistant to chlorine disinfection and can survive for days in

adequately chlorinated pools; therefore, suboptimal chlorination of the pool might not be the sole factor contributing

to the occurrence of an outbreak.

Three outbreaks of laboratory-confirmed cryptosporidiosis

occurred during the 1999 summer swim season. During the

2000 summer swim season, three substantial outbreaks of

Cr. parvum occurred that were related to swimming in

municipal pools. In August 2000, an outbreak occurred in

Colorado that affected 112 persons attending a private pool

party. In June 2000, the two other cryptosporidiosis outbreaks,

one in Ohio affecting 700 persons and the other in Nebraska

affecting 225 persons (27), occurred among members of private swim clubs. In both outbreaks, the protracted nature of

the outbreaks during >2 months was the result of repeated

recontamination of the pools by infected persons continuing

to swim; 37 (18%) of 205 persons interviewed in the

Nebraska outbreak admitted to swimming while symptomatic, and 32% swam while ill or during the 2 weeks after their
Vol. 51 / SS-8 Surveillance Summaries 15

illness (27). Another outbreak (Florida, August 2000) was

associated with the outbreak that occurred in Ohio. A family

who were members of the implicated swim club in the Ohio

outbreak were vacationing with a sick child. While in a pool

in Florida, the infant had two fecal accidents. The resulting

outbreak caused five cases of diarrheal illness and two hospitalizations.

Eight other outbreaks of cryptosporidiosis occurred in

treated venues during the 2000 swim season. Two outbreaks

of gastroenteritis occurred in untreated venues: one in a freshwater lake in Minnesota in July 2000 and one in a Massachusetts pond in July 1999 (Appendix B).

Four cases of laboratory-confirmed primary amebic meningoencephalitis attributed to Naegleria fowleri occurred during this 2-year reporting period. All four persons were aged

<19 years. Three of the persons died from infection after having contact with a pond, lake, or mud hole. The fourth person’s

freshwater exposure could not be determined; that person had

fallen from a jet ski into an unspecified body of water, sustained injuries, and died from an infection shortly after it was

detected.

Bacteria. Nine recreational outbreaks involving gastroenteritis were attributed to bacterial pathogens, and five of the

nine were linked to freshwater sources. Five cases (Wisconsin,

August 1999) of Es. coli O157:H7 occurred among persons

who had visited the same swimming

beach. After a review of potential risk

factors, the only common link found

was swimming at the implicated

beach. The popular beach

featured a shallow, dammed area that

was used for wading. Total and fecal

coliforms were detected in water

samples collected before and during

the outbreak, although the levels

detected did not exceed levels of

EPA-recommended guidelines for

microbiologic quality of water (22).

One sample that was tested for

Es. coli O157:H7 was negative.

Es. coli O157:H7 was implicated in

another outbreak among 36 persons

(August 1999) who visited a state park

in Washington. Es. coli O121:H19 was

implicated in an outbreak in a Connecticut community (July 2000).

Shigella sonnei was implicated in two

outbreaks that occurred at swimming

beaches in Minnesota (July and

August 2000).

Nonfreshwater sources were implicated in four bacterial

recreational water outbreaks involving gastroenteritis. In

March 1999, an outbreak of Ca. jejuni was associated with a

private pool in Florida that did not have continuous chlorine

disinfection and reportedly had ducks swimming in the pool.

Outbreaks of Shigella flexneri and Es. coli O157:H7 (Missouri, September 2000 and Nebraska, June 1999) occurred

among children using unchlorinated wading pools. Fecal

accidents were factors contributing to the contamination of

the water in both outbreaks. Es. coli O157:H7 also was implicated as a cause of illness in an outbreak (Florida, September

1999) among two young children who had been playing in

ditch water. Both clinical specimens and water samples tested

positive for Es. coli O157:H7.

Two nongastroenteritis-related recreational water outbreaks

were also reported. One outbreak of leptospirosis was reported

among 21 persons who participated in an adventure race in

Guam in July 2000 (Table 8). These persons reported multiple outdoor exposures, including running through jungles

and savannahs, swimming in a river and a reservoir, and bicycling and kayaking in the ocean. Leptospira was confirmed by

serology, and an epidemiologic investigation demonstrated

that swimming in the reservoir, submerging one’s head in the

water, and swallowing water while swimming were risk factors for illness. Water samples were not tested, and an

FIGURE 4. Waterborne-disease outbreaks of gastroenteritis associated with recreational

water, by etiologic agent and type of exposure — United States, 1999–2000

Cryptosporidium

parvum 44.4%

Shigella species

8.3%

O157:H7

11.1%

AGI* 16.7%

NLV†

8.3%

Cryptosporidium

parvum 7.1%

Escherichia coli

O157:H7

21.4%

AGI* 28.6%

NLV†

14.3%

Etiologic agent in fresh water (n = 14)

Other§

11.1%

Giardia 7.1%

Shigella species . 14.3%

Escherichia coli

O121:H19

7.1%

Etiologic agent in treated water (n = 22)

Campylobacter jejuni

4.5%

Shigella species.

4.5%

Cryptosporidium

parvum 68.2%

AGI* 9.1%

NLV†

4.5%

Shigella / Cryptosporidium 4.5%

Escherichia coli

O157:H7 4.5%

Fresh water

38.9%

Treated water

61.1%

Etiologic agent (n = 36) Type of exposure (n = 36)

Escherichia coli

* Acute gastrointestinal illness of unknown etiology. †

Norwalk-like virus. §

These included outbreaks of Campylobacter jejuni, Giardia, Escherichia coli O121:H19 and one mixed

Shigella/Cryptosporidium outbreak.
16 MMWR November 22, 2002

environmental assessment of the reservoir was not conducted.

The second nongastroenteritis-related recreational water outbreak was an outbreak of Pontiac fever epidemiologically

linked to use of a whirlpool at a hotel.

Viruses. During 1999–2000, three outbreaks of NLV

(Calicivirus) that affected a total of 202 persons were reported.

Two NLV outbreaks occurred in untreated systems; one outbreak of NLV occurred (Idaho, June 1999) at a resort and

water park and affected 25 persons. The pool implicated in

the investigation was untreated because the source of the pool’s

water was a natural hot springs that was high in mineral content. The investigators noted that geothermal pools used for

swimming are not required to be regulated by public health

officials in that locale. The pool implicated by the

investigation also had been implicated in a previous outbreak

of NLV in June 1996.

Other. During 1999–2000, six recreational water outbreaks

involving gastroenteritis of unknown etiology were reported.

One outbreak (Florida, August) involved a motel pool that

was cloudy and dirty at the time of exposure. Nine persons

who swam in this pool and did not share any other common

exposure became ill with gastroenteritis. Disinfectant residuals and operation of the filtration system at the time of the

investigation were deficient. Problems were also noted with

the equipment used for adjusting pH.

Another outbreak (Florida, August 1999) among 38 persons who visited a beach park was attributed to both Sh. sonnei

and Cr. parvum (28). Illness was epidemiologically linked to

playing in an interactive fountain at the park, ingesting water,

and consuming food and beverages at the fountain. The

fountain’s recirculation, filtration, and disinfection systems

were not approved by the health department and were inadequate or not completely operational at the time of its use.

Samples of the fountain water tested positive for coliforms

but did not test positive for fecal coliforms. Nevertheless, the

cause of the outbreak was determined to be the fountain, which

was closed until the health department’s concerns could be

remedied.

Three cases of chemical keratitis (Vermont, February 2000)

resulted from exposure to bromine in a hotel swimming pool.

Bromine levels were >5 ppm (acceptable bromine levels are

1–3 ppm), and the pH level was >8.5. Patrons who spent

time with their heads underwater with their eyes open were

affected.

Twelve persons affected in an outbreak (Texas, September

1999) reported symptoms that included exhaustion, sore

muscles, headache, chills, and fever after attending a conference at a guest ranch. One woman reported a miscarriage

during her illness. Exposure to a hot tub, defined as either

immersion or being near the hot tub, was associated with

illness. Although clinical specimens (urine, blood, sputum,

and throat swabs) were tested for organisms, including

Leg. pneumophila serogroups 1 and 6, influenza virus, parainfluenza virus, and adenovirus, no infectious agent was identified. No testing for biologic or chemical agents was performed

on water samples because the hot tub had already been drained,

refilled, and hyperchlorinated before the environmental

investigation.

During the 1999–2000 reporting period, 15 outbreaks of

dermatitis were identified (Table 9). Three of these outbreaks

were associated with swimming in freshwater and were

assumed to be cercarial dermatitis caused by contact with the

larval form (cercariae) of schistosomes, which are present in

freshwater environments. Two of these dermatitis outbreaks

occurred in lakes in California that were associated with past

cases of cercarial dermatitis. The onset of dermatitis occurred

within hours after swimming in the lake and resolved after a

limited number of days (median days of illness were 2 and 3

days [range: 2–3 and 3–5 days], respectively). The 12 remaining outbreaks were associated with pool and hot tub use and

affected 5–29 persons each. P. aeruginosa was confirmed in

clinical isolates in 3 of the 12 outbreaks and was confirmed

in water/filter samples in five outbreaks, two of which also

had a clinical isolate. In eight of these outbreaks of dermatitis, specific treatment deficiencies or problems were identified. Outbreaks in Arkansas (June 1999), Florida (August

2000), Colorado (December 1999), and Washington (March

2000) were attributed to deficiencies in treatment.

In one outbreak of dermatitis (Maine, February 2000), nine

persons reported rash in addition to headache, fever, fatigue,

and sore throat (29). Swimming in the hot tub or swimming

in the pool was a risk factor. The pool and hot tub were on

separate filtration systems, and both were used by the majority of persons in the outbreak. Low levels of free chlorine were

found in the pool and hot tub, but the presence of chlorinate

isocyanurates (chlorine stabilizers) might have influenced

measured levels of free chlorine. A clinical isolate of P. eruginosa

was obtained from an ill person; P. aeruginosa also was isolated

from the pool filter even after the pool had been cleaned twice.

P. aeruginosa was isolated from clinical specimens and

water samples in an outbreak at a Colorado hotel that

affected 19 persons in February 1999 (28), 13 of whom were

children aged <15 years. Symptoms were not limited to rash;

they included diarrhea, vomiting, nausea, fever, fatigue, muscle

aches, joint pain, swollen lymph nodes, and subcutaneous

nodules on hands and feet. Because of the severity and range

of symptoms, clinical specimens were examined for enteric

bacterial and parasitic pathogens as well as Legionella species,

Leptospira species, and Entamoeba histolytica but did not test

positive for any of these etiologic agents. Swabs taken from
Vol. 51 / SS-8 Surveillance Summaries 17

TABLE 10. Waterborne-disease outbreaks associated with occupational exposures — United States, 1999–2000 (n = 2)

Number

State Year Month Class* Etiologic agent Exposure of cases Source Setting

Hawaii 1999 Aug IV Leptospira Contact with pond water 2 Pond Outdoor landscaping

Minnesota 2000 Aug III Pontiac fever† High-pressure cleaning 15 Plant lagoon Sugar beet plant

using lagoon water

* On the basis of epidemiologic and water-quality data provided on CDC form 52.12. †

Endotoxin was also isolated from environmental samples; the role of endotoxin is unclear.

the hot tub floor and rail were positive for P. aeruginosa and

other Pseudomonas species. Pool and hot tub records indicated

that chlorine and pH had declined below the state-mandated

levels at the time of exposure. Epidemiologic evidence implicated the hot tub as the likely vehicle of exposure for the outbreak. In both the Colorado outbreak and the Maine outbreak

that occurred in February 2000, an offsite contractor had been

engaged to monitor disinfectant and pH levels. Insufficient

communication between pool staff and the remote monitoring company might have contributed to extended periods of

usage with inadequate disinfection (28).

Outbreaks Associated with Occupational

Exposure to Water

Two outbreaks not associated with drinking or recreational

water exposure were reported during this period (Table 10).

One outbreak of leptospirosis (Hawaii, August 1999) occurred

among persons landscaping a pond. Leptospirosis was confirmed serologically for the two persons who had contact with

the pond. Both persons reported multiple skin abrasions and

were exposed to the pond water for a period of 5–10 days.

One of the two persons was hospitalized.

An outbreak of acute respiratory illness occurred among

sugar beet processing plant workers (Minnesota, August 2000).

Of the 15 cases identified, 13 were hospitalized. Serology for

4 (26.7%) of the 15 persons tested positive for Leg.

pneumophila; three (20.0%) persons were confirmed positive

for Leg. pneumophila by sputum polymerase chain reaction

(PCR). Fourteen (93.3%) of the 15 persons worked on a crew

that had performed high-pressure cleaning in one area of the

plant; the fifteenth patient had conducted high-pressure cleaning elsewhere in the plant. The sources of water for the highpressure cleaning contained 105 colony-forming unit (CFU)/

mL of Leg. pneumophila and endotoxin levels of 22,200

endotoxin units/mL. Although the attack rate, symptoms, and

laboratory findings were consistent with an outbreak of Pontiac

fever, endotoxin exposure might have contributed to this

outbreak.

Previously Unreported Outbreaks

Three previously unreported drinking water outbreaks that

occurred in 1995 and 1997 were submitted during this

reporting period (Table 11). An illegal cross-connection

(Washington, July 1995) between a domestic water supply

TABLE 11. Waterborne-disease outbreaks associated with drinking water that were not included in the previous surveillance

summaries — United States, 1995–1997 (n = 3)*

Number Type of

State Year Month Class* Etiologic agent of cases system§ Deficiency¶ Source Setting

Washington 1995 Jul III Giardia intestinalis** 87 Com 4 Well Community

California 1997 Nov III Nitrite (sodium metaborite) 7 Com 4 Mixed river/groundwater Hospital cafeteria

New York 1997 Dec I Norwalk-like virus 1,450 Ncom 3 Well Ski resort

* An outbreak is defined as 1) >2 persons experiencing a similar illness after either ingestion of drinking water or exposure to water used for recreational

purposes and 2) epidemiologic evidence that implicates water as the probable source of illness.

† On the basis of epidemiologic and water-quality data provided on CDC form 52.12.

§ Com = community; Ncom = noncommunity; Ind = individual; Community and noncommunity water systems are public water systems that serve >15

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/year (e.g., factories or schools), whereas transient systems do not (e.g., restaurants, highway rest

stations, or parks). Individual water systems are not owned or operated by a water utility and 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).

** Thirty-three persons had stool specimens that tested positive for G. intestinalis. One specimen tested positive for Entamoeba coli. One other specimen

tested positive for Blastocystis hominis. One cultured specimen tested positive for Campylobacter jejuni.
18 MMWR November 22, 2002

and an irrigation system at a plant nursery resulted in contamination of multiple wells in a community. Eighty-seven

cases of gastroenteritis were reported, and one hospitalization

was recorded. G. intestinalis was determined in 33 (52.4%) of

63 stool specimens; Entamoeba coli and B. hominis were each

found in one stool specimen. One (7.1%) of 14 stool specimens that were cultured for Ca. jejuni tested positive.

NLV was implicated as the cause of an outbreak (New York,

December 1997) of 1,450 cases at a restaurant at a ski resort.

Epidemiologic data implicated water or consumption of ice

made from water as the cause of the outbreak. The environmental assessment revealed possible problems with the well

operation and location. The chlorinator for the well had been

malfunctioning and had already been disconnected before the

assessment. Testing of the water by the local health department determined that neither a free nor total chlorine residual

was detectable in the potable water supply and indicated the

presence of fecal coliforms. In addition, the well was located

<24 inches away from a stream. During the period the chlorinator was not functioning, the pump for the well had been

continuously pumping water. Surface water that might have

been introduced into the water supply, plus a deficiency in

treatment of the water, played a key role in the outbreak.

Seven persons who were either employees or visitors at a

hospital (California, November 1997) were symptomatic for

methemoglobinemia in one outbreak. An epidemiologic

investigation indicated that the only shared exposure among

these persons was a visit to the hospital cafeteria and the consumption of a carbonated beverage with ice from the selfservice soda dispenser. The onset of symptoms occurred 1–5

minutes after or while drinking a carbonated beverage. One

person was hospitalized, and no deaths occurred. The environmental investigation discovered a cross-connection in the

plumbing system that might have allowed water from the cooling tower, which had been recently shock-treated with

sodium metaborate, to be drawn into the drinking water system. Sodium metaborate has been associated with nitrate poisoning and methemoglobinemia in past incidents (30).

Outbreaks Not Classified as WBDOs

Outbreaks attributed to drinking water that was contaminated or potentially contaminated at the point of use rather

than at the source or in the distribution system are not classified as WBDOs. Six outbreaks, causing illness among a total

of 102 persons, are in this category. None of the six outbreaks

reflected a common vehicle of contamination: one outbreak

of Cr. parvum was epidemiologically associated with ice consumption; a school-based outbreak of Sh. sonnei was related

to consumption of water from a dispenser stored in a

bathroom facility; a third outbreak involved water taken from

a garden hose (the water had been stored in an ice chest

before consumption at a private residence); and a fourth outbreak associated with bottled water that might have been contaminated at the point of use. Two of the six reported

point-of-use outbreaks involving a suspected chemical exposure occurred in food service facilities, but water testing was

not performed to verify the presence of the chemical; and,

because of the relatively limited number of cases associated

with these incidents, the epidemiologic information was not

adequate to include these incidents as outbreaks.

Data from six other possible or confirmed outbreaks were

also not included in this analysis. One confirmed outbreak of

leptospirosis was related to travel outside the United States or

its territories and therefore was excluded. This outbreak

occurred among student travelers who became ill after their

return from Ecuador. Three cases of leptospirosis were confirmed by laboratory testing among the cohort, and four

additional cases were suspected. Three other outbreaks of

G. intestinalis, Cr. parvum, and NLV could not be included

in the analysis. Although these outbreaks were probably caused

by a recreational water exposure, the data provided did not

meet the criteria for inclusion (i.e., the outbreaks did not meet

the criteria for Classes I–IV).

Two additional outbreaks were excluded because of inadequate information: one outbreak of dermatitis caused by

in-home bathing and one potential drinking water outbreak

of Cr. parvum in a New England community. This outbreak

of Cr. parvum occurred in a community near another reported

community outbreak of G. intestinalis and Cr. parvum in 1999.

The pond implicated in the recreational water outbreak of

G. intestinalis also served as a surface water source, which was

intermittently mixed into the municipal drinking water that

supplied the community. However, not all the persons received

their drinking water from the municipal water source.

Although raw surface water samples later tested positive for

Cr. parvum by immunomagnetic spectroscopy (IMS), household water samples either tested negative, were not tested, or

the results were not provided. The epidemiologic information and water-quality information provided were not conclusive.

Discussion

Considerations Regarding Reported

Results

The WBDO surveillance system provides information concerning epidemiologic and etiologic trends in outbreaks. In
Vol. 51 / SS-8 Surveillance Summaries 19

where the majority of outbreaks actually occurred. An increase

in the number of outbreaks reported could either reflect an

actual increase in outbreaks or an improved sensitivity in

surveillance practices.

Recognition of WBDOs also is dependent on certain outbreak characteristics; outbreaks associated with serious illness

or affecting a substantial number of persons are more likely

to receive attention from health authorities. Outbreaks

involving acute diseases, including those characterized by a

FIGURE 5. Number of waterborne-disease outbreaks associated with drinking water, by

year and etiologic agent — United States, 1971–2000 (n = 730)*

0

10

20

30

40

50

60

1971 1974 1977 1980 1983 1986 1989 1992 1995 1998

Year

AGI†

Chemical

Viral

Parasitic

Bacterial

Number of outbreaks

* The total from previous reports has been corrected from n = 691 to n = 688. †

Acute gastrointestinal illness of unknown etiology.

FIGURE 6. Number of waterborne-disease outbreaks associated with drinking water, by

year and type of water system — United States, 1971–2000 (n = 730)*

0

10

20

30

40

50

60

1971 1974 1977 1980 1983 1986 1989 1992 1995 1998

Year

Individual

Noncommunity

Community

Number of outbreaks

* The total from previous reports has been corrected from n = 691 to n = 688.

previous years, a decrease in the number of drinking waterassociated outbreaks had been observed. However, the

cumulative number of drinking water outbreaks reported for

the 1999–2000 period demonstrates a reversal of this trend

(Figures 5 and 6). The number of recreational water outbreaks

has been gradually increasing for the past 15 years and is at

the highest level since CDC began receiving such reports in

1978.

Although the number of outbreaks reported through

the surveillance system has

increased, the significance of this

increase is unclear. Whether this

indeed reflects a true increase in the

number of outbreaks that occurred

in the United States is unknown.

Not all outbreaks are recognized,

investigated, and then reported to

CDC or EPA, and studies have not

been performed that assess the sensitivity of this system and indicate

what percentage of actual outbreaks this system is able to detect.

Multiple factors exist that can

influence whether WBDOs are

recognized and investigated by

local, territorial, and state public

health agencies: the size of the outbreak; severity of disease caused by

the outbreak; public awareness of

the outbreak; routine laboratory

testing for organisms; requirements for reporting cases of diseases; and resources available to the

local health departments for surveillance and investigation of probable outbreaks. This surveillance

system probably underreports the

true number of outbreaks because

of the multiple steps required

before an outbreak is identified

and investigated. In addition,

changes in the capacity of local,

county, and state public health

agencies and laboratories to detect

an outbreak might influence the

numbers of outbreaks reported in

each state relative to other states.

The states with the majority of

outbreaks reported during this

period might not be the states
20 MMWR November 22, 2002

short incubation period, are more readily identified than

outbreaks associated with chronic, low-level exposure to an

agent (e.g., certain chemicals) or are associated with organisms that have a longer incubation period (e.g., certain parasitic organisms). Outbreaks involving larger drinking water

systems (e.g., community systems) are more likely to be

detected than outbreaks that involve noncommunity systems

because these systems serve mostly nonresidential areas and

transient populations. Outbreaks associated with individual

systems are the most likely to be underreported because they

typically involve a limited number of persons. Recreational

outbreaks where persons congregate in one venue and then

are geographically dispersed can be difficult to document.

The identification of the etiologic agent of a WBDO

depends on the timely recognition of the outbreak so that

appropriate clinical and environmental samples can be collected. The laboratory involved in the testing of specimens

must have the capacity and capability to test for a particular

organism. In certain cases, specific tests must be requested.

Routine testing of stool specimens at laboratories will include

tests for the presence of enteric bacterial pathogens and might

also include an ova and parasite examination. However,

Cr. parvum, one of the most commonly reported waterborne

parasites, is not often included in standard ova and parasite

examinations and in certain instances, must be specifically

requested (31). During 1999–2000, tests for NLV and other

possible agents of viral origin were rarely performed or documented in the outbreaks that were reported to CDC. 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. Furthermore, certain outbreaks can substantially

alter the relative proportion of cases of waterborne disease

attributed to a particular agent. The number of reported cases

is typically an approximate figure, and the method and accuracy of the approximation vary among outbreaks.

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. 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

are collaborating on a series of epidemiologic studies to assess

the magnitude of nonoutbreak waterborne illness associated

with consumption of municipal drinking water and with

exposure to recreational marine and freshwaters.

Outbreaks Associated with Drinking

Water

The number of outbreaks reported during 1999 (15) and

2000 (24) is higher than the number reported during 1997

(7) and 1998 (10). As described previously, the number of

drinking water outbreaks had declined (2,3). The increase in

reported outbreaks should be carefully interpreted. Although

the number of drinking water outbreaks has changed, the

total number of persons affected by a drinking water outbreak during 1999–2000 (n = 2,027) is comparable to what

was initially reported in 1997–1998 (n = 2,038) and 1995–

1996 (n = 2,567) (2,3). Changes in surveillance and reporting of outbreaks might have improved detection of outbreaks

affecting limited, private systems that in turn, affect a relatively limited number of persons. However, the increase in

outbreaks that affect persons in limited, private systems merits further investigation by public health and water-quality

agencies.

Certain states reported drinking water outbreaks for the

first time in >10 years (e.g., Connecticut since 1976 or Utah

since 1986). California reported multiple drinking water outbreaks after reporting no outbreaks in 1997 and 1998, and

compared with other years during 1990–2000, the number

of reported outbreaks in California increased slightly. The

number of outbreaks reported by Florida also increased.

Although the numbers of reported outbreaks increased overall, the seasonality of the drinking water outbreaks is consistent with previous years, with the number peaking during the

summer months. The observed increase in the number of outbreaks is associated with an increase in outbreaks associated

with consumption of untreated water from both surface and

groundwater sources, but specifically private wells.

The percentage of drinking water outbreaks associated with

surface water during 1999–2000 was 17.9% (i.e., seven outbreaks) (Figure 2). This percentage is higher than the 11.8%

reported during 1997–1998 period (i.e., two outbreaks).

However, three of the seven surface water outbreaks reported

during 1999–2000 were associated with the direct ingestion

of surface water without any treatment or with inadequate

individual treatment. Two of these outbreaks were associated

with consumption of water during outdoor excursions where

point-of-use treatment (e.g., filtration or disinfection) might

have been attempted and was either inadequate to protect

health or was inconsistently or incorrectly applied. The third

outbreak occurred after a household had run out of potable

water and instead served untreated creek water to their guests.

These three outbreaks illustrate that the public might be

unaware that surface water, despite its clarity, is prone to

contamination by organisms. Surface waters should not be
Vol. 51 / SS-8 Surveillance Summaries 21

¶ Additional information is available at http://www.nsf.org.

** Additional information is available at http://www.epa.gov/safewater/

gwr.html.

directly consumed without being treated at the point of use

or boiled. Manufacturers of point-of-use devices and the

National Sanitation Foundation (NSF) provide information

regarding different devices, instructions for use, and their

ability to make water safe for human consumption.¶ The

remaining four outbreaks comprise approximately 11% of all

drinking water outbreaks, an equivalent percentage to that

reported in 1997–1998. These four outbreaks were associated with systems that routinely received treatment. One outbreak of giardiasis occurred at a resort (Colorado, August 2000)

served by a noncommunity system. The increased demand

for water during the summer, coupled with multiple treatment failures, resulted in the delivery of unfiltered and

nondisinfected water to the resort. These multiple failures

illustrate the importance of routine maintenance, specifically

among noncommunity systems, which do not have consistent demand for water year-round. Two outbreaks (Florida,

March 1999 and August 1999) were associated with crossconnections: one to an irrigation well and another to a toilet.

Another surface water outbreak (Ohio, August 2000) at a fairgrounds was suspected to have resulted from back-siphonage

into the drinking water from an animal manure site. These

outbreaks indicate that even when treatment of water at the

source is adequate, deficiencies in the distribution system or

at the home can result in illness. Such deficiencies are preventable, and the public should be informed of how to detect

and avoid creating cross-connections.

Twenty-eight (71.8%) of the 39 outbreaks related to drinking water were associated with groundwater sources. This

number is an 87% increase from the number reported in the

previous period (i.e., 15). Seventeen of the 28 outbreaks

(60.7%) were linked to consumption of untreated groundwater; eight of 28 (28.6%) outbreaks were associated with

treatment deficiencies; and three (10.7%) were linked to

deficiencies in the distribution system. The observed pattern

of deficiencies is contrary to what was observed in the previous reporting period, where the majority of groundwater outbreaks were associated with treatment or distribution system

problems. This pattern indicates that untreated groundwater

systems are increasingly associated with outbreaks of illness.

Groundwater systems, with the exception of systems influenced by surface water, are not routinely required to use filtration or treatment that would be expected to reduce the

number of pathogens in the water. EPA’s pending GWR** is

expected to establish multiple barriers in groundwater systems to protect against bacteria and viruses in drinking water

from groundwater sources and should establish a targeted

strategy to identify groundwater systems at high risk for fecal

contamination.

Twenty-six of these 28 groundwater outbreaks had a well as

the implicated water source, and two were linked to a spring.

The percentages of outbreaks associated with wells and springs

were similar during this reporting period to the 1997–1998

period. Although GWR is expected to have public health benefits, these protections extend primarily to community groundwater systems. Of the 26 well-related outbreaks that occurred

during the 1999–2000 period, only eight of 26 were associated with community wells. Ten were associated with individual private wells, and eight were associated with

noncommunity wells. These systems would not necessarily

benefit from the promulgation of GWR, and therefore, the

quality of water in wells remains a public health concern.

Approximately 14–15 million households in the United States

rely on a private, household well for drinking water each year,

and >90,000 new wells are drilled throughout the United States

each year (32). In addition, contamination of a private well is

not only a health concern for the household served by the

well, but can impact households using other nearby water

supplies and could potentially contaminate the aquifer.††

Additional education efforts should be targeted towards 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.

Three outbreaks were associated with direct consumption

of water from irrigation systems, comprising approximately

8% of drinking water outbreaks (Figure 2). Cross-connections

to irrigation systems were implicated as contaminating factors in three other irrigation-related outbreaks. Irrigation

waters are not regulated under the Safe Drinking Water Act,

because they are typically intended for agricultural purposes,

not for human consumption. Therefore, irrigation water would

not be expected to be treated to reduce the level of microorganisms or other contaminants potentially in the water to the

same standards as water intended for consumption. In one

outbreak, children drank directly from an irrigation

canal while playing outside a home. In two other outbreaks,

water was directly consumed from an irrigation tap by sports

team members. In the first instance, the sports team consumed

water from a labeled irrigation tap despite being informed

that the water was not intended for consumption. In the

second instance, two teams drank from taps on the field

†† Although EPA does not regulate private wells and will not regulate them

as part of the proposed GWR, EPA lists recommendations for protecting

private water supplies at http://www.epa.gov/safewater/pwells1.html and

provides links to other sources of information.
22 MMWR November 22, 2002

because no other source of potable water was available on

field.

The multistate outbreak of Sa. Bareilly, which was detected

through CDC’s Salmonella Outbreak Surveillance Algorithm

(SODA), epidemiologically implicated the consumption of

bottled water as a risk factor for illness. This is the first widespread outbreak implicating bottled water in the United States.

Previous bottled water outbreaks occurred in New Jersey in

1973 (33), Pennsylvania in 1980 (34), and in the Northern

Mariana Islands in 1993 (4). Bottled water standards and regulations, unlike the majority of drinking water standards, are

not set and enforced by EPA but by FDA. FDA regulates

bottled water as a packaged food product and bases their

bottled water standards on EPA’s tap water standards. In

addition, bottled water might be subject to state and voluntary industry regulation. Bottled water, before this outbreak,

had not been identified as a vehicle for transmission of infectious organisms in the United States, although a bottled

water outbreak of Ca. jejuni associated with consumption of

water bottled in Greece was documented during the 1997–

1998 surveillance period (2). Because of the wide geographic

distribution of bottled water products, an outbreak associated with the consumption of bottled water would be difficult to recognize. FDA, EPA, CDC, and the bottled water

industry together should address concerns regarding consumption of bottled water and public health.

Overall, the number of outbreaks associated with the five

drinking water deficiencies (untreated surface water, untreated

groundwater, treatment deficiency, distribution system deficiency, and unknown/miscellaneous deficiency) increased in

each category from the 1997–1998 levels. The percentage of

outbreaks caused by a treatment deficiency and distribution

system problem decreased relative to reported increases in the

other three categories. Although problems with treatment and

with distribution systems remain critical concerns for safe

drinking water, the public’s lack of understanding of the risk

associated with consumption of untreated water and the

assumption that all water is suitable for consumption is a

concern also.

The relative proportion and number of outbreaks associated with different water systems also differs from the figures

from the 1997–1998 period (Figure 2). Outbreaks in community systems increased from 8 to 11 outbreaks (37.5%

increase); noncommunity outbreaks doubled from 5 to 11;

and individual system outbreaks quadrupled, increasing from

4 to 17 outbreaks. However, the proportion of outbreaks in

community systems decreased from 47.1% during 1997–1998

to 28.2% during 1999–2000, whereas the relative proportion

of outbreaks in individual systems increased from 23.5% during 1997–1998 to 43.6 during 1999–2000. In addition, the

number of outbreaks reported that were associated with individual systems during this period is the highest reported level

since 1984. The drinking water quality of community systems, which typically have been the focus of increased EPA

regulation, has continually improved. But noncommunity

systems and individual systems, which are not regulated to

the same extent, are continuing problems. The majority of

these individual system outbreaks are linked to currently

unregulated groundwater supplies, specifically private wells.

The populations served by these systems merit increased

attention by public health officials.

The etiologic agent was not identified in 17 (43.6%) of 39

outbreaks (Figure 2). These outbreaks of unknown etiology

comprised the largest group of outbreaks, followed by outbreaks caused by bacteria (nine), parasites (seven), viruses

(four), and chemicals (two). During 1997–1998, parasites

accounted for the largest percentage of the 17 outbreaks (six

[35.3%]), followed by unidentified pathogens (five [29.4%]),

bacteria (four [23.5%]), chemicals (two [11.6%]), and viruses

(zero [0%]). The number of outbreaks per type of agent were

increased for all categories during 1999–2000, with the

exception of chemicals. Although the number of reported

viral outbreaks increased, indicating an improvement in the

availability and usage of laboratory detection methods during previous years, viral outbreaks are probably substantially

underreported. Although viruses were suspected in other outbreaks, specifically in those of unknown etiology, testing for

viruses was not performed. The technology for detection of

viruses in stool and water samples has improved, but testing

for viruses is 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 organisms are available

from CDC (35). Investigators are also encouraged to contact

CDC and EPA regarding testing of water samples.

Only two outbreaks of chemical origin were identified during this surveillance period, the same number as was reported

during the 1997–1998 period. One outbreak related to a spill

of sodium hydroxide at a community water treatment plant

demonstrated the need for safe water treatment practices. The

other outbreak was a single case of methemoglobinemia in an

infant who required hospitalization after having been fed

boiled water taken from a private well. Coordination of public health messages is critical; an intervention that was

intended to reduce the transmission of infections agents concentrated the chemicals present in the water. These figures, as

in the past, probably underrepresent the actual waterborne

chemical poisonings that occur. Multiple factors can explain

the low reporting rate, including the likelihood that 1) the

majority of waterborne chemical poisonings typically occur
Vol. 51 / SS-8 Surveillance Summaries 23

Because swimming is essentially a shared water activity or

communal bathing, rinsing of soiled bodies and overt fecal

accidents cause contamination of the water. Unintentional

ingestion of recreational water contaminated with pathogens

can then lead to gastrointestinal illness, even in nonoutbreak

settings (36,37). Fresh and marine waters are also subject to

other modes of contamination from point sources (i.e., sewage releases), watersheds (i.e., runoff from agriculture and residential areas), and floods.

Outbreaks involving gastroenteritis are more frequently

observed during the swimming season, which usually starts

on Memorial Day weekend (the last weekend in May) and

ends Labor Day weekend (the first weekend in September).

However, swimming also occurs year-round in indoor venues

and in states with more temperate climates. Outbreaks of illness by month (Figure 3) include two outbreaks that occurred

noticeably outside the summer months: one outbreak in a

Florida pool in March and another outbreak in an indoor

pool in Wisconsin in January.

As during the previous reporting period, Cr. parvum

accounted for the largest percentage of outbreaks involving

gastroenteritis (44.4%), followed by Es. coli O157:H7

(11.1%), NLV (8.3%), and Shigella (8.3%). An outbreak of

G. intestinalis was also reported in 1999. The last reported

recreational water outbreak of Giardia occurred in 1996. Outbreaks of Ca. jejuni, Es. coli O121:H19, and a mixed Sh. sonnei/

Cr. parvum outbreak were also reported for the first time to

the surveillance system. Outbreaks of unknown etiology comprised 16.7% of the recreational water outbreaks involving

gastroenteritis.

in private residences and affect a relatively limited number of

persons; 2) exposures to chemicals through drinking water

might cause illness that is difficult to link to a chemical exposure; 3) the mechanisms for reporting waterborne chemical

poisonings to the WBDO surveillance system are not as

established for chemicals as they are for WBDOs attributed

to infectious agents; and 4) health-care providers and those

affected might not as easily recognize chemical poisonings.

As a result of these factors, WBDOs of chemical poisonings

are less likely to be reported to public health officials.

Strengthening the capacity of local and state public health

epidemiologists and environmental health specialists to

detect and investigate outbreaks remains a priority at CDC

and EPA. As part of that effort, CDC and EPA should partner with the states, CSTE, and the Association of Public

Health Laboratories to develop training materials and online

resources that would be useful and easily accessible to local

and state public health personnel. Although no federal regulation exists for monitoring private wells, developing educational materials targeted towards the general public, informing

them of ways to maintain the safety and water quality of their

wells would be valuable. In addition, health messages regarding the consumption of nonpotable water and appropriate

point-of-use treatment should be developed and distributed

to the public.

Outbreaks Associated with Recreational

Water

Of the 59 recreational WBDOs, those involving gastroenteritis were most frequently reported (n = 36). The 15

outbreaks reported in 1999 and 21

outbreaks reported in 2000 equal

or surpass the number reported in

1998, which previously was the

highest number of outbreaks

involving recreational water-related

gastroenteritis reported in one year

since the inception of the surveillance system. Together, the outbreaks involving gastroenteritis

reported during the 1999–2000

period are higher than the 18 outbreaks documented in the previous

reporting period (Figures 7 and 8).

Since 1989, the number of gastroenteritis-related outbreaks has been

gradually increasing, and this

increase is statistically significant

(p = 0.01).

FIGURE 7. Number of waterborne-disease outbreaks associated with recreational water,

by year and illness — United States, 1989–2000 (n = 229)*

0

5

10

15

20

25

30

35

40

1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

Other

Dermatitis

Meningoencephalitis

Gastroenteritis

Number of outbreaks

* The total from previous reports has been corrected from n = 171 to n = 170.
24 MMWR November 22, 2002

Twenty-two (61.1%) of the 36 outbreaks of gastroenteritis

occurred in treated systems (i.e., pools) that would usually be

expected to be chlorinated or disinfected to prevent transmission of infectious agents after unintentional ingestion.

However, the term treated system might pertain to systems not

routinely treated, including wading pools, interactive

fountains, and in one case, an untreated pool that was served

by a natural hot springs source. Multiple interrelated factors

can impede disinfection in treated venues, including an

increased bather load in a pool, high levels of organic material (e.g., fecal material or environmental or skin debris) and

ultraviolet light, all of which deplete chlorine residuals that

usually maintain protection in the system. In certain outbreaks,

fecal material was indicated on the report as a contributing

factor to the outbreak; the majority of fecal accidents were

attributed to young children who were in or near the water at

the time the accident occurred.

Unlike previous years, a substantial number of different

bacterial and viral organisms were reported as causing gastrointestinal illness in these treated recreational water venues

(Figure 9). Nevertheless, >66% of these outbreaks were

attributed to Cr. parvum (Figure 4). Unlike other organisms,

which are more susceptible to the levels of chlorine typically

found in a pool, Cr. parvum is highly chlorine-resistant and

requires increased levels of chlorine and longer contact times

with chlorine for inactivation. Cr. parvum can survive for days

in public health-mandated chlorine concentrations required

for pools. In addition, its relatively limited size (4–6 μm) can

allow it to pass through particulate filtration systems during

recirculation of water in the pool.

Because a low number of oocysts

might cause illness in a person, even

ingestion of a limited amount of

water can cause infection.

Although the number of Cr.

parvum outbreaks has been steadily

increasing during 1990–2000,

multiple explanations could exist

for the increase. The properties of

the organism, coupled with the

popularity of swimming and the

tendency of persons to aggregate in

larger water venues, increases the

likelihood that swimming water

can become contaminated and that

swimmers will ingest the water and

become infected. However, the

increases in outbreaks could be

explained by a higher awareness of

Cr. parvum as a potential cause of

illness among swimmers by the public health community and

the recreational water industry and, as a result, are more likely

to be detected.

The majority of these Cr. parvum outbreak investigations

noted inadequate pool maintenance. Although low chlorine

levels are unlikely to have been the cause of the outbreaks, the

frequent reporting of low chlorine levels in these outbreaks

indicates a disturbing lack of awareness concerning the role

of chlorine and pH control as the major protective barrier

against infectious disease transmission in pools. Inadequate

disinfectant levels in any pool increases the risk for transmission of chlorine-sensitive pathogens (e.g., Es. coli O157:H7

or Shigella species) if an infected swimmer contaminates the

pool. Pool operators and staff should be appropriately trained

regarding the spread of recreational water illnesses and the

critical role of pool maintenance (i.e., disinfection, pH control, and filtration) in preventing WBDOs.§§

Fourteen outbreaks involving gastroenteritis after freshwater exposure were reported during 1999–2000, compared with

eight during 1997–1998. Es. coli O157:H7 accounted for the

most outbreaks of known etiology (three), followed by NLV

(two), Shigella species (two), Es. coli O121:H19 (one),

G. intestinalis (one), and Cr. parvum (one). Four outbreaks

were of unknown etiology. Certain outbreaks occurred in

beach areas that had substantial numbers of families bathing

and swimming in the water. Again, a common element noted

§§ Guidelines for pool operators and other information related to recreational

water illnesses is available at http://www.cdc.gov/healthyswimming.

FIGURE 8. Number of outbreaks involving gastroenteritis associated with recreational water,

by year and illness — United States, 1978–2000 (n = 146)

0

5

10

15

20

25

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

Year

Number of outbreaks
Vol. 51 / SS-8 Surveillance Summaries 25

¶¶ Additional information is available at http://www.epa.gov/waterscience/

beaches.

in these reports was the presence of diaper-aged children in

the water, diaper-changing on the beach, and even washing

off young children in the water. One incident involved persons who swam in a lake that was had posted signs indicating

that the lake was unsafe for swimming.

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 swimming in freshwater venues. EPA, as part of the Beaches Action Plan, is

developing guidelines and information for users of freshwaters.¶¶ Geothermal pools and hot springs should be examined

closely. In one outbreak, pools in a complex were exempt from

public health regulation because they were naturally occurring hot springs and mineral waters. Hot springs, which feature high levels of minerals and elevated temperatures, are

potentially ideal venues for microbial growth or contamination. These springs and geothermal pools pose an increased

risk to swimmers, compared with treated pools because of

their lack of disinfection and filtration. Improved consumer

and staff education and supplementary treatment might be

necessary to prevent future outbreaks in these enclosed freshwater pools.

Twelve of the 15 outbreaks of dermatitis were associated

with hot tub or pool use. The majority of these reports of

dermatitis are associated with deficient maintenance and

inadequate disinfection of the

water. The higher temperatures

commonly found in hot tubs

deplete disinfectant levels at a more

rapid rate; hot tub operators should

be encouraged to actively check

and maintain adequate disinfectant

levels. In addition to rashes, reports

have been received of other symptoms. In Alaska, three of 29 persons reported nausea. In the two

Maine outbreaks, persons also

reported headache, fatigue, and

other symptoms. The Colorado

outbreak was notable for its severe

symptomatology and an extended

duration of illness. Extended and

painful rashes associated with

P. aeruginosa outbreaks are unusual

but have been documented

(38,39). One report (39) also indicates that a substantial number of children are being affected by these outbreaks. In the

Colorado outbreak of P. aeruginosa, the persons affected were

primarily children, but no indication was provided that age

was a risk factor for infection. More remarkable is the

observed duration of illness. Certain persons reported chronic

illness (i.e., rash, joint pain, abdominal pain, and chest pain)

that lasted >6 weeks. Using remote pool monitoring services

in two of these outbreaks underscores the need for training

pool staff regarding the role of monitoring service and prompt

communication between service and pool operators when

problems are detected.

Three outbreaks of dermatitis that occurred after persons

swam in fresh or marine water were presumed to be caused by

an allergic reaction to the cercariae, the larval form of certain

nonhuman species of schistosomes. Cercarial dermatitis was

an identified problem in two of these lakes, and signs posted

by the health department regarding this problem were ignored

by swimmers. The extent of the problem of cercarial dermatitis caused by freshwater exposure is unknown, although it

probably occurs more frequently than what is reported to the

surveillance system. As schistosomes occur naturally in ecosystems that bring snails and birds or aquatic mammals close

together, a substantial number of freshwater lakes in the United

States might cause illness among swimmers. Swimmers should

pay careful attention to where they swim, avoid shallow swimming areas known to be appropriate snail habitats in lakes

associated with cercarial dermatitis, and report any incidents

to their local health department to prevent further illnesses.

FIGURE 9. Number of outbreaks involving gastroenteritis associated with recreational water,

by water type — United States, 1985–2000 (n = 135)

0

5

10

15

20

25

1985–1986 1987–1988 1989–1990 1991–1992 1993–1994 1995–1996 1997–1998 1999–2000

Fresh

Treated

Year

Number of outbreaks
26 MMWR November 22, 2002

The four deaths associated with primary amebic meningoencephalitis (PAM) reported during the 1999–2000

period were all linked to freshwater exposure. Typically, these

cases are associated with swimming in freshwater bodies in

the late summer months because N. fowleri, which has been

implicated in >90% of the cases reported to CDC, proliferate in warm, stagnant waters. Previous cases of PAM have

been reported from states with more temperate climates (e.g.,

California, Florida, and Texas) or from areas with hot springs.

The amoebas associated with PAM are believed to enter

through the nasal passage. Preventing forceful entry of water

up the nasal passages during jumping or diving by holding

one’s nose or wearing nose plugs could reduce the risk for

infection.

Swimming in waters contaminated by animal urine was

the likely explanation for an outbreak of leptospirosis among

persons participating in an adventure race in Guam. Leptospira

species can be found frequently in wild animal urine, and can

be contracted through inhalation of aerosolized water or

ingestion of water while swimming. Leptospirosis can also be

acquired through abrasions. In this instance, the exposure was

associated with immersion of persons’ heads in a body of water

while they swam and swallowed water. Although outdoor

swimming is not necessarily dangerous, swimmers should be

educated regarding the potential risks resulting from swimming in areas that are not secured from wild animal use.

An increased level of bromine, which is used to disinfect

pools and hot tubs, caused certain cases of chemical keratitis.

Inadequate disinfection of a whirlpool resulted in an outbreak

of legionellosis among 20 persons who stayed at a motel. Safe

disinfection practices and appropriate pool maintenance protocols should be communicated to operators and managers

of facilities that treat recreational water.

Outbreaks Associated with Occupational

Exposures to Water

Two outbreaks that do not fit into the previous categories

were reported to CDC by Minnesota and Hawaii. Outbreaks

associated with exposure to aerosolized water have previously

occurred but have not been reported to the WBDO surveillance system (40,41). These outbreaks are discussed in this

report to demonstrate that water exposures are not limited to

ingestion and contact (e.g., through swimming), and these

outbreaks are preventable. Using barrier masks to prevent

inhalation of aerosolized water or disinfection of water that is

not being used for drinking or swimming purposes could have

prevented the respiratory illnesses associated with these two

outbreaks.

Conclusion

Data collected as part of the national WBDO surveillance

system are used to describe the epidemiology of waterborne

diseases in the United States. Data 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 agencies need to detect and recognize WBDOs 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 could 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).

One repeated observation regarding outbreak data collected

as part of the WBDO system was that the timely collection of

clinical specimens and water samples for testing and commencement of an environmental investigation would have

resulted in an improved ability to detect the outbreak’s etiologic agent and the source of water contamination. However,

the course of an investigation is influenced by 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, a common observation is that investigations

cannot always be completed thoroughly. WBDO outbreak

investigations typically require input from 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 be 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 drinking water and recreational water treatment and regarding collection of
Vol. 51 / SS-8 Surveillance Summaries 27

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 tests for parasites should be made to CDC’s

Division of Parasitic Diseases, NCID, at 770-488-7760.

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 NCID website at http://www.cdc.gov/ncidod;

• CDC’s Healthy Swimming website at http://ww.cdc.gov/

healthyswimming; includes recreational water health communication materials for the general public and pool

maintenance staff (e.g., information regarding disinfection, guidelines on response to fecal accidents [42], fact

sheets concerning recreational water illnesses), and an

outbreak investigation toolkit that can be used by public

health professionals;

• 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 770-488-7760 or by fax at 770-488-7761.

Acknowledgments

The authors thank the following persons for their contributions

to this report: state waterborne-disease surveillance coordinators;

state epidemiologists; state drinking water administrators; Susan

Shaw, M.S., M.P.H., Office of Ground Water and Drinking Water,

EPA; Robert Tauxe, M.D., Division of Bacterial and Mycotic

Diseases, NCID, CDC; Roger Glass, M.D., Ph.D., Steve Monroe,

Ph.D., and Marc-Alain Widdowson, M.A., Vet.M.B., M.Sc.,

Division of Viral and Rickettsial Diseases, NCID, CDC; Matthew

Arduino, Dr.P.H. and Joe Carpenter, Division of Healthcare Quality

and Promotion, NCID, CDC; Mark Eberhard, Ph.D., Mary

Bartlett, Ali Khan, M.D., James Maguire, M.D., and Dennis

Juranek, D.V.M., Division of Parasitic Diseases, NCID, CDC; and

Lorraine Backer, Ph.D., Division of Environmental Hazards and

Health Effects, National Center for Environmental Health, CDC.

References

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

FL: CRC Press, Inc., 1986.

2. 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):1–35.

3. 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.

4. 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.

5. 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.

6. 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.

7. Environmental Protection Agency. 40 CFR Part 141. Water programs:

national interim primary drinking water regulations. Federal Register

1975;40:59566–74.

8. Pontius FW, Roberson JA. Current regulatory agenda: an update. Journal of the American Water Works Association 1994;86:54–63.

9. Pontius FW. Implementing the 1996 SDWA amendments. Journal of

the American Water Works Association 1997;89:18–36.

10. Environmental Protection Agency. Announcement of the drinking

water contaminant candidate list; notice. Federal Register

1998;63:10274–87.

11. Environmental Protection Agency. 40 CFR Parts 141 and 142. Drinking water; national primary drinking water regulations; filtration,

disinfection; turbidity, Giardia lamblia, viruses, Legionella, and heterotrophic bacteria; final rule. Federal Register 1989;54:27486–541.

12. Environmental Protection Agency. 40 CFR Parts 141 and 142. Drinking water; national primary drinking water regulations; total coliforms

(including fecal coliforms and E. coli); final rule. Federal Register

1989;54:27544–68.

13. Environmental Protection Agency. 40 CFR Parts 141 and 142. Drinking water; national primary drinking water regulations; total coliforms;

corrections and technical amendments; final rule. Federal Register

1990;55:25064–5.

14. Environmental Protection Agency. 40 CFR Parts 9, 141, and 142.

National primary drinking water regulations: interim enhanced surface water treatment; final rule. Federal Register 1998;63:69477–521.

15. Environmental Protection Agency. 40 CFR Parts 9, 141, and 142.

National primary drinking water regulations: long term 1 enhanced

surface water treatment rule; final rule. Federal Register 2002;67:1812–44.

16. Environmental Protection Agency. 40 CFR Parts 9, 141, and 142.

National primary drinking water regulations: long term 1 enhanced

surface water treatment and filter backwash rule; proposed rule. Federal Register 2000;67:19046–150.

17. Environmental Protection Agency. 40 CFR Parts 9, 141, and 142,

National primary drinking water regulations: filter backwash recycling

rule; final rule. Federal Register 2001;66:31085–105.

18. Environmental Protection Agency. 40 CFR Parts 141 and 141.

National primary drinking water regulations: ground water rule; proposed rules. Federal Register 2000;65:30193–274.

19. Environmental Protection Agency. 40 CFR Parts 9, 144, 145, and

146. Underground injection control regulations for class V injection

wells, revision; final rule. Federal Register 1999;64:68545–73.
28 MMWR November 22, 2002

20. Environmental Protection Agency. 40 CFR Part 141. National primary drinking water regulations: monitoring requirements for public

drinking water supplies; final rule. Federal Register 1996;61:24353–88.

21. Environmental Protection Agency, 40 CFR Parts 9, 141, and 142.

National primary drinking water regulations for lead and copper.

Final rule. Federal Register 2000;65:1949–2015.

22. US Environmental Protection Agency, Office of Water. Ambient

water quality criteria for bacteria—1986. Cincinnati, OH: National

Service Center for Environmental Publications, 1986. EPA publication no. 440584002.

23. Dufour AP. Health effects criteria for fresh recreational waters.

Research Triangle Park, NC: US Environmental Protection Agency,

Office of Research and Development, Health Effects Research Laboratory, 1984; EPA publication no. 600184004.

24. US Environmental Protection Agency, Office of Water. Factoids: drinking water and ground water statistics for 2000. Washington, DC: US

Environmental Protection Agency, Office of Water, 2001. EPA publication no. 816K01004. Available at http://www.epa.gov/cgi-bin/

claritgw.

25. US Environmental Protection Agency. EPA safe drinking water information system factoids: FY 1999 inventory data. Washington, DC:

US Environmental Protection Agency, 2002. Available at http://

www.epa.gov/safewater/data/99factoids.pdf.

26. Anonymous. Blastocystis hominis: a new pathogen in day-care centers?

Can Commun Dis Rep 2001;27:76–84.

27. CDC. Protracted outbreaks of cryptosporidiosis associated with swimming pool use—Ohio and Nebraska, 2000. MMWR 2000;50:406–10.

28. CDC. Outbreak of gastroenteritis associated with an interactive water

fountain at a beachside park—Florida, 1999. MMWR 2000;49:565–8.

29. CDC. Pseudomonas dermatitis/folliculitis associated with pools and hot

tubs—Colorado and Maine, 1999–2000. MMWR 2000;49:1087–91.

30. CDC. Methemoglobinemia attributable to nitrite contamination of

potable water through boiler fluid additives—New Jersey, 1992 and

1996. MMWR 1997;46):202–4.

31. Jones JL, Lopez A, Wahlquist SP, Nadle J, Wilson M. Survey of clinical laboratory practices, parasitic diseases. Clinical Infectious Diseases

(in press).

32. US General Accounting Office. Drinking water: information on the

quality of water found at community water systems and private wells.

Washington, DC: US General Accounting Office, 1997. GAO publication no. GAO/RCED-97-123.

33. CDC. Foodborne & waterborne disease outbreaks [Annual summary

1973]. Atlanta, GA: US Department of Health, Education, and Welfare, CDC, 1974. Publication no. 76-8185.

34. CDC. Water-related outbreaks [Annual summary 1980]. Atlanta, GA:

US Department of Health and Human Services, CDC, 1981. Publication no. 82-8385.

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

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

nonpoint sources of contaminated water. International Journal of

Environmental Health Research 1991;1:21–31.

37. Seyfried PL, Tobin RS, Brown NE, Ness PF. Prospective study of

swimming-related illness. I. Swimming-associated health risk. Am J

Public Health 1985;75:1068–70.

38. Berrouane YF, McNutt LA, Buschelman BJ, et al. Outbreak of severe

Pseudomonas aeruginosa infections caused by a contaminated drain in a

whirlpool bathtub. Clin Infect Dis 2000;31:1331–7.

39. Fiorillo LM, Zucker M, Sawyer D, Lin AN. Pseudomonas hot-foot

syndrome. N Engl J Med 2001;345:335–8.

40. CDC. Sustained transmission of nosocomial Legionnaires disease—

Arizona and Ohio. MMWR 1997;46:416–21.

41. CDC. Legionnaires disease associated with a whirlpool spa display—

Virginia, September–October, 1996. MMWR 1997;46:83–6.

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

[Notice to readers]. MMWR 2001;50:416–7.
Vol. 51 / SS-8 Surveillance Summaries 29

Appendix A

Selected Case Descriptions of Outbreaks Associated with Drinking Water

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

Parasites

January

1999

June

2000

July

2000

August

2000

September

2000

Florida

Minnesota

New

Mexico

Colorado

Florida

G. intestinalis

G. intestinalis

G. intestinalis

G. intestinalis

G. intestinalis

2

12

4

27

2

Persons became ill after drinking well water. Environmental

inspection revealed that pigs were maintained 15 feet from

the well. Fecal coliforms were not detected in the water

samples, but data indicated inadequate levels of chlorine.

Initial water testing confirmed the presence of fecal coliforms

in the drinking water where persons were working in a wildlife refuge. Further investigation of the well revealed that a

drain line from the well pit had been connected to the sewer

line, allowing contamination of the water by raw sewage.

Persons drinking water provided by others during a rafting

trip became ill. The water was either incorrectly purified

river water or river water that was untreated before consumption.

A resort experienced multiple failures in the pumping mechanism and filtration system during drinking water treatment

that resulted in untreated river water entering the drinking

water supply. The water supply included a mix of spring

water and conventionally treated river water that usually was

pumped into and held in a water storage tank. A failure in

the primary system was reported; the backup pump was used,

and multiple filtration cartridges were later determined to

be defective. Although water in the holding tank was usually chlorinated, because of the demands placed on the system during the summer season, chlorine might not have had

adequate time to inactivate Giardia cysts. Giardia was identified in samples from 5 of the 27 affected persons and in

the finished water in the holding tank.

Persons became ill after drinking water contaminated from

a cross-connection between watering troughs for exotic animals and the drinking water system, which created an

opportunity for back-siphonage of the trough water.

Coliforms were present in the water, but fecal coliforms were

not detected in the water samples. Data indicated inadequate

levels of chlorine.
30 MMWR November 22, 2002

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

September

2000

December

2000

Bacteria

June

1999

August

1999

November

1999

New

Hampshire

Florida

Missouri

New York

Texas

G. intestinalis

Cryptosporidium

parvum

Salmonella

Typhimurium

Ca. jejuni and

Es. coli

O157:H7

Es. coli

O157:H7

5

5

124

781

22

Household members used a private well where the waterfiltration system had inadvertently been shut off during a

1-month period by construction workers. The water was not

otherwise treated (e.g., chlorination).

An outbreak occurred among persons who had consumed

water from a community system well. The well had a series

of breaks and repairs, including a break reported days before

initial reports of illness. Investigation revealed low levels of

chlorine (0.03 mg/L) in the tap water.

Persons consumed water from a community well that was

routinely disinfected by chlorine, but investigators reported

that chlorine had been inadequate at the time of the outbreak. Seventeen persons were hospitalized.

A fairground was served primarily by chlorinated water, but

certain vendors used water from an unchlorinated shallow

well to make beverages and ice. Epidemiologic data associated illness (including 71 hospitalizations and two deaths)

with consumption of water from that well. Drought conditions had lowered the water table and heavy rains occurring

during the fair might have contributed to contamination of

the well by surface water. Dye tests revealed a cross-connection

between a dormitory septic system and a well on the fairgrounds, but did not confirm the presence of a hydraulic

connection between a nearby manure storage site and the

implicated well. However, testing had occurred 2 months

after the outbreak and after Hurricane Floyd had passed

through the area, raising the water table. Therefore, the possibility of a previous connection during the time of the fair

could not be ruled out. Although stool sampling of ill persons indicated the presence of both Es. coli O157:H7 and

Ca. jejuni, only Es. coli O157:H7 was identified in water samples.

A city well water supply was implicated because all 22 persons received municipal water and had no other common

exposures. Water quality data indicated that the routinely

chlorinated water was inadequately chlorinated for weeks

during the beginning of the outbreak. Subsequent to the

outbreak, a new chlorination system was installed for the

water supply.
Vol. 51 / SS-8 Surveillance Summaries 31

April

2000

June

2000

July

2000

August

2000

August

2000

Idaho

Idaho

California

Utah

Ohio

Es. coli

O157:H7

Ca. jejuni

Es. coli

O157:H7

Ca. jejuni and

Es. coli

O157:H7

Es. coli

O157:H7

4

15

5

102

29

Children reportedly drank water from the canal in their backyard while playing. Water from the affected household and

from the canal located near the home was tested. Coliforms

were not present in the home’s tap water, but 100 fecal

coliforms/100 mL were present in the canal water. Agricultural runoff might have contributed to contamination of

the canal water.

Contaminated groundwater was implicated in this outbreak

among persons attending a geology summer camp. The

source of water was a spring box, a device used to collect

water, that was incorrectly constructed, potentially allowing

contamination by surface water and agricultural runoff.

Water samples from the spring box were positive for total

coliforms but negative for fecal coliforms. Breaks in the line

running from the spring to the camp were noted. Water in

the campsite hose tested positive for both total and fecal coliforms.

Campers ingested filtered creek water both directly and in

food reconstituted with creek water. They reported defecating near the campsite, and they had defecated in the water

while swimming. In addition, deer droppings, a possible

source of Es. coli O157:H7, were found near the creek.

Although campers also reported swimming in the creek,

swimming could not be implicated as an exposure. Illness

was confirmed through laboratory tests.

Participants at a football camp drank from an irrigation system tap that was not intended for human consumption. No

hospitalizations or deaths were reported. Ca. jejuni was the

most commonly isolated organism among submitted stool

specimens and was also isolated from water samples; Es. coli

O157:H7 and O111 were also isolated from stool specimens, but shiga toxins for these organisms were not found

in water samples.

Persons who had attended a county fair were confirmed for

Es. coli O157:H7 by stool culture. Additional cases of

gastrointestinal illness were identified in the community;

however, either they could not be laboratory-confirmed as

Es. coli O157:H7 or they were probably secondary cases.

Nine of the 29 culture-confirmed persons were hospitalized.

Other potential risk factors (e.g., a particular food item,

beverage, or direct exposure to animals) could not be implicated. However, consumption of food and beverages sold

within a particular area of the fairgrounds was a substantial

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description
32 MMWR November 22, 2002

April–

August

2000

10 Southeastern

states:

Alabama,

Arkansas,

Georgia,

Kentucky,

Louisiana,

Missouri,

North

Carolina,

Tennessee,

Virginia,

and West

Virginia

Salmonella

Bareilly

84

exposure. Investigation revealed that the branch of the distribution system supplying the vendors in the implicated

area also supplied an animal show barn. Spigots connecting

hoses to both the animal areas and the concession stands

were not equipped with backflow-prevention devices. Therefore, possible back-siphonage might have resulted in contamination of the water supply used for human consumption.

Although, water samples taken from the municipal system

supplying the fair and water taken after the closure of the

fair were negative for coliforms, one spigot serving the

implicated vendor area tested positive for coliforms, but negative for Es. coli.

The outbreak was detected by CDC’s Surveillance Outbreak

Detection Algorithm. Forty-three of the 84 persons were

enrolled in a case-control study with 76 matched controls.

The outbreak was associated with drinking bottled water

and water from private wells or springs. Twenty-five persons

drank water from private wells; Sa. Bareilly was recovered

from one patient’s well. The majority of source wells were

located in a limestone area in the southeastern United States;

wells drilled in limestone are subject to contamination from

different sources, including surface water. Among eight persons who did not drink well or spring water in the week

before illness, the consumption of either of two brands of

water bottled by one company was epidemiologically implicated as a risk factor for illness. A Food and Drug Administration (FDA) traceback investigation of the two implicated

brands (spring water and “infant water,” water marketed specifically for consumption by infants) linked the bottled

water to one facility in the southeastern United States. An

investigation of the facilities determined that the two implicated products had different sources, but water flowed

through the same lines before bottling. Infant water was

derived from a municipal source and passed through multiple treatment steps at the facility (separate from the spring

water), and then stored before the bottling process. The bottling process included two filtration steps, ultraviolet irradiation and an nonautomated ozonization step. The bottled

spring water came from water transported from a spring in

north Georgia. After the spring water was fluoridated at the

plant, the spring water shared the same treatment and bottling path as the infant water. Logs from daily in-house testing did not indicate coliforms; however, raw spring water

samples tested by an independent laboratory in June were

positive for total coliforms. Environmental samples collected

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description
Vol. 51 / SS-8 Surveillance Summaries 33

Viruses

July

1999

June

2000

June

2000

New

Mexico

West

Virginia

Kansas

Small roundstructured virus

Norwalk-like

virus

Norwalk-like

virus

70

123

86

by CDC and FDA during the investigation did not yield Sa.

Bareilly, but one of the 105 samples taken from a lot of bottled

water produced in September was positive for Es. coli, and

two of 105 samples were positive for other coliforms. Treatment provided should have been adequate to prevent contamination of the bottled water, but finding coliforms implies

that interruption of treatment or suboptimal operation might

have allowed fecal contamination of the bottled water.

Inspection of the treatment process did not reveal any obvious deficiencies; therefore, the source of the contamination

remains unknown.

At a scout camp, a spring box influenced by surface water

was the key factor in the outbreak. Small round-structured

virus was observed in stool samples from three of 22 specimens submitted. An association with consumption of water

or any drinks prepared with water was observed, although

the numbers were not statistically significant. No other food

items were associated with the outbreak. Assessment of the

drinking water system indicated that the spring box was situated at a lower elevation than the latrines and other buildings with individual septic systems. Water samples taken from

the well and distribution system were positive for fecal coliforms.

Multiple cohorts of camp attendees reported gastrointestinal illness occurring during a multiweek period. Consumption of food items and a history of swimming were ruled

out as vehicles of transmission. The epidemiologic information could not statistically implicate water as the vehicle of

exposure; however, the environmental investigation determined that two wells that provided the drinking water were

located near a lagoon and one well was visibly contaminated

with sewage. Fecal coliforms were isolated from both wells.

Persons who attended two different parties at a reception

hall on 2 separate days became ill. The facility’s well water

was the only common source between the two groups, and

the water was not filtered or treated. Norwalk-like virus was

isolated from individual stool specimens from both groups.

Inspection of the well serving the facility indicated improper

well construction, and sampled water tested positive for

coliforms.

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description
34 MMWR November 22, 2002

July

2000

Chemicals

April

1999

November

1999

January

1999

March

1999

March

1999

Norwalk-like

virus

Nitrate

Sodium

hydroxide

Unknown

Unknown

Unknown

147

1

2

4

3

6

Untreated well water at a camp facility was implicated. Testing identified fecal and total coliforms in one of the wells

and in the areas of the distribution system serving the recreational vehicles and tent areas in the campground.

An infant was fed formula prepared with boiled tap water

from a private well for >2 days after the household ran out

of bottled water normally used to prepare infant formula.

The infant became ill, was hospitalized, and was treated to

reverse increased methemoglobin levels. Subsequent testing

of the tap water revealed the presence of fecal coliforms and

nitrate. Inorganic tests for metals were negative.

Lack of a check valve at a community well resulted in spillage of approximately 200 gallons of sodium hydroxide into

a 110,000-gallon well during a multihour period. Although

only two persons reported illness, a cohort estimated at 100–

1,000 persons might have been affected. The first person to

report an adverse effect suffered a first-degree burn from

showering in the contaminated water. The second person

suffered cramps, presumably from ingestion of the water.

A well was improperly constructed, and water was not routinely disinfected or filtered. Persons interviewed indicated

water had been turbid before the outbreak. Two water samples

indicated coliforms were present.

An outbreak occurred at an apartment building that usually

received municipal water from a well disinfected with chlorine. The outbreak involved a cross-connection within the

apartment complex to an irrigation well. Total coliforms were

found in samples taken after the outbreak had occurred, but

fecal coliforms were not found. A stool specimen from

one of the affected persons tested negative for bacterial and

parasitic enteric pathogens.

Outbreak involved a cross-connection to an irrigation well

from a municipal surface water system. The municipal

water system was routinely treated and filtered. The irrigation well in question was in unsatisfactory sanitary condition and was located 25 feet from a commercial septic system

and 10 feet from a garbage container. No clinical testing was

performed.

California

Wisconsin

New Jersey

Florida

Florida

Florida

Unidentified etiologic agents

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description
Vol. 51 / SS-8 Surveillance Summaries 35

May

1999

July

1999

July

1999

August

1999

April

2000

Florida

California

Washington

Washington

Florida

Unknown

Unknown

Unknown

Unknown

Unknown

3

31

46

68

71

An outbreak occurred after persons in the household began

drinking well water. Well was located 10 feet from a chicken

coop. Duration of illness was approximately 60 days. No

clinical results were provided. Chlorine residuals were not

detected in water samples.

An outbreak occurred among persons who visited a camp

cabin. Diarrhea, vomiting, and cramps were reported.

Median incubation period was 24 hours, and median duration of illness was 24 days. The well used for drinking water

was not routinely disinfected or filtered. Water samples tested

positive for fecal coliforms.

Persons had consumed untreated creek water, but tests for

Cryptosporidium parvum, G. intestinalis, Shigella species,

Salmonella, Ca. jejuni, Es. coli O157:H7, and Yersinia

enterocolitica performed on stool specimens were all negative. One stool specimen was positive for Blastocystis hominis

and another for Endolimax nana. The median incubation

period before onset of illness among the 46 persons was 34

hours (range: 10–95.5 hours), and their median duration of

illness was 38 days (range: 2–192 days).

Participants of a soccer match reported gastrointestinal illness. The most commonly reported symptoms were diarrhea (72%), vomiting (78%), and nausea (84%). No one

food or beverage item was implicated, but drinking any beverage prepared on site was a substantial risk for illness.

Although contaminants were not identified, the soccer match

took place at a polo field that reportedly had horse manure

at the site. Coliforms were found in the water tested, but

samples taken from the wellhead and the clubhouse were

negative for Es. coli. Stool specimens tested negative for

enteric bacteria and parasites.

Clinical testing was attempted when the outbreak occurred

among persons who drank water from untreated wells. A

sinkhole in a local lake had developed, allowing water to be

directed into the aquifer. Before the sinkhole was plugged,

water from 78 of the surrounding wells was tested. Nineteen of the wells were negative for coliforms; 33 were positive for total coliforms; and 26 were positive for fecal

coliforms. Cryptosporidium was found in one of the wells.

After the sinkhole was plugged, 58 wells were negative for

coliforms; 21 wells were positive for total coliforms; and none

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description
36 MMWR November 22, 2002

June

2000

September

2000

Florida

California

Unknown

Unknown

2

63

was positive for fecal coliforms. No enteric pathogens were

identified in one clinical specimen that was submitted. No

viral testing of either clinical specimens or water samples

was reported.

An outbreak was associated with consumption of untreated

well water; two persons reported diarrhea that lasted approximately 60 days. The stool specimen collected from one person tested negative for Giardia but positive for B. hominis.

The well was located in an area that had experienced flooding and heavy rainfall before the outbreak. The affected persons indicated that dark residue and air bubbles had appeared

in their water around the time of illness. Environmental

assessment confirmed that the well was in unsatisfactory sanitary condition and noted the presence of grit and air bubbles

in the water. Total coliforms were observed in water samples

taken after disinfection of the well, although fecal coliforms

were absent. The conclusion of the investigators was that

the well might have been contaminated by surface water.

An outbreak occurred after football players consumed water

after a game from an irrigation system coupler located on

the playing field. The water was not intended for human

consumption and was subject to contamination from backsiphonage of surface water that collected around the sprinkler heads and control valves. Both total and fecal coliforms

>16,000 most probable number/100 mL were isolated from

the irrigation source water. No hospitalizations or deaths

resulted. Because the median incubation period was 12 hours

(range: 5–31 hours) and the median duration of illness

was also 12 hours (range: 1 hour–3 days), the outbreak was

probably of viral or bacterial origin.

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description
Vol. 51 / SS-8 Surveillance Summaries 37

Appendix B

Selected Case Descriptions of Outbreaks Associated with Recreational Water

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

Parasites

July and

August

1999

July

1999

July

1999

June

2000

June

2000

Wisconsin

and Florida

Minnesota

Massachusetts

Ohio

Nebraska

Cryptosporidium

parvum

Cr. parvum

Giardia

intestinalis

Cr. parvum

Cr. parvum

10

18

700

225

Both outbreaks were linked to private swimming pools; chlorine levels had not been tested in either of these outbreaks.

Chlorine levels were inadequate at a trailer park swimming

pool because the chlorinator needed repair.

The common exposure for persons affected was swimming

in a local pond. Giardiasis was laboratory-confirmed.

Although the source water was not tested for G. intestinalis,

water tests for the pond indicated high levels of total

coliforms.

A swimming pool at a private club was implicated. An

investigation determined that additional risk factors for

cryptosporidiosis (e.g., drinking municipal water, eating

unpasteurized food, or visiting a local zoo) were not statistically significant. However, the investigation did determine

that a substantial risk factor for illness was oral contact with

water. The pool consisted of a zero-entry–level pool (i.e., a

simulated beach entry) that was connected to both a baby

wading pool and adult pool with a water slide. Review of

pool records indicated that on >2 days, the chlorine residual

was inadequate, including on days when the bather load was

high and air temperature hot. In addition, multiple fecal

accidents had been reported. Testing of water samples at

CDC, using Environmental Protection Agency (EPA)

Method 1622, demonstrated the presence of Cr. parvum

oocysts in the water.*

Surveillance conducted by a county health department

revealed a cluster of laboratory-confirmed cases of

cryptosporidiosis, primarily among persons who were members of two private clubs with swimming facilities (clubs A

and B). Case-control studies were conducted among members of the two clubs. Swimming and being splashed with

pool water at club A was statistically associated with illness.

Club A had four pools: outdoor adult and baby pools and

10 and 6,

respectively

*CDC. Protracted outbreaks of cryptosporidiosis associated with swimming pool use—Ohio and Nebraska, 2000. MMWR 2000;50:406–10.
38 MMWR November 22, 2002

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

June

2000

July

2000

July

2000

July

2000

July

2000

July

2000

Georgia

Minnesota

Minnesota

Florida

South

Carolina

Minnesota

Cr. parvum

Cr. parvum

Cr. parvum

Cr. parvum

Cr. parvum

Cr. parvum

36

7

6

3

26

220

indoor adult and baby pools. The two outdoor pools shared

a filtration system, whereas the two indoor pools had separate filtration systems but were connected by a pipe used to

equilibrate the water level of the pools. Fecal accidents had

occurred before the outbreak. Review of the pool maintenance logs revealed a 2-day period when the baby pool had

not been chlorinated.†

Persons reported illness after attending a private pool party

where, in addition to swimming in a neighborhood pool,

party attendees also swam in an inflatable pool. Inadequate

chlorine levels were detected in the neighborhood pool. No

treatment was documented for the inflatable pool.

Inadequate chlorination and filtration were documented in

this outbreak among attendees at a day camp.

Information from interviews implicated a hotel pool in an

outbreak of cryptosporidiosis among members of a baseball

team. Both whirlpool and pool samples were negative for

Cr. parvum.

Inadequate water quality and low chlorine levels were documented in an outbreak at an apartment complex. Fecal

material had been visible in the pool at the apartment complex.

Water-quality data from a neighborhood pool implicated in

an outbreak of cryptosporidiosis were inconclusive. Coliform

tests were negative; however, these tests were conducted

after the outbreak had occurred and the pool had been treated

with high levels of chlorine. Chlorine levels at the time of

and after the outbreak were unreported. Certain factors might

have contributed to the outbreak, including a history of

symptomatic children swimming in the pool before the outbreak and increased rain activity that might have decreased

the water quality by diluting chlorine levels or facilitated

runoff into the pool.

An outbreak of cryptosporidiosis occurred at a public swimming beach. A total of 220 persons reporting illness were

asked questions regarding swimming exposure and food consumed while at the beach. Exposure to the water (i.e., getting the head wet while swimming) was associated with

†CDC. Protracted outbreaks of cryptosporidiosis associated with swimming pool use—Ohio and Nebraska, 2000. MMWR 2000;50:406–10.
Vol. 51 / SS-8 Surveillance Summaries 39

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

August

2000

August

2000

August

2000

August

2000

August

2000

Bacteria

August

1999

Colorado

Florida

Florida

Florida

Minnesota

Wisconsin

Cr. parvum

Cr. parvum

Cr. parvum

Cr. parvum

Cr. parvum

Es. coli

O157:H7

112

19

5

5

4

5

illness. The inspection conducted by the county health

department did not identify any plumbing deficiencies at

the beach clubhouse. Reports of construction on a sewer

line were investigated, but the investigators determined that

the source of contamination was persons washing babies in

the lake while changing diapers on the beach.

The epidemiologic investigation implicated swimming in

the main pool or having contact with the water as a risk

factor for illness among the persons who attended a private

party at a municipal pool. Although the main pool shared a

silica-sand filtration system with a smaller, adjacent wading

pool, contact with the wading pool was a substantial risk

factor.

Exposure to the pool at a resort was a substantial risk factor

for infection. In addition, infection was associated with

longer times of exposure to the resort pool water. Complaints

of cloudy water and diapered children swimming in the pool

were reported.

This outbreak was linked to the outbreak that occurred in

Ohio in June 2000. A family from Ohio who were members

of the implicated swim club vacationed in Florida. While in

a pool in Florida, the ill infant had two fecal accidents.

Illness was associated with swimming in a pool, and one

infected child reportedly swam while ill. Water quality

information was not available.

This outbreak was detected through routine surveillance. All

four were interviewed by the state health department and

queried about history of illness and exposures to water, food,

animals, and child care centers. All four persons reported

swimming in the same municipal swimming pool. No corrective action was taken. The outbreak was reported after

the pool had closed at the end of the swimming season.

Swimmers who had visited the same beach became ill. The

popular beach featured a shallow, dammed area that was used

for wading. Total and fecal coliforms were detected in water

samples collected before and during the outbreak, although

the levels did not exceed regulatory levels for microbiologic

quality of water. One sample that was tested for Es. coli

O157:H7 was negative.
40 MMWR November 22, 2002

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

August

1999

May

2000

July

2000

July

2000

Washington

Wisconsin

Connecticut

Minnesota

Es. O157:H7

Legionella

pneumophila

Es. coli

O157:H7

Shigella sonnei

36

20

11

15

A freshwater outbreak occurred among visitors to a state park.

Swimming in the lake, getting lake water in the mouth, and

swallowing water from the lake were all associated with illness. In addition, Es. coli O157:H7 was laboratory-confirmed

among the affected persons, including seven hospitalizations,

and isolated from samples of sediment from the lake as well

as the water.

A whirlpool was implicated in a serologically confirmed

outbreak of Pontiac fever among 20 persons who visited a

hotel. L. pneumophila group 5 bacteria were isolated from

the whirlpool but not from the swimming pool. Additional

samples collected from sand filters, a water heater, and a

shower also were negative for L. pneumophila. Disinfectant

levels for both the whirlpool and pool were inadequate at

the time of the outbreak. Analysis of responses to questionnaires administered to motel visitors revealed that only whirlpool and swimming pool exposures were substantial risk

factors for illness. No other possible common exposures demonstrated associations with illness. The investigation concluded from both the epidemiologic and environmental data

that the whirlpool was the likely vehicle of transmission.

The outbreak occurred among persons who lived in or visited the same community during the last 2 weeks of July. An

environmental assessment of both well water and lake water

was conducted. The well water system was found to be in

compliance with drinking water standards, and samples from

two wells and ice made from this water were all negative for

total coliforms. Lake water sampled after the outbreak was

negative for Es. coli and shiga toxins but was positive for

total and fecal coliforms. No other environmental problem

at the lake was identified, and animal feces collected from

local wildlife tested negative for Es. coli O157 or any other

shiga toxin–producing isolates. The environmental assessment, combined with epidemiologic evidence, implicated

swimming at the lake and swallowing water as substantial

risk factors for illness. During this same time period, a toddler with severe diarrhea reportedly had swum in the water

during a 1-week period while ill.

Fifteen persons reported illness after swimming at a freshwater lake. Of these, 13 tested positive for Sh. sonnei, one

for Cr. parvum, and one for both organisms.
Vol. 51 / SS-8 Surveillance Summaries 41

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

August

2000

Viruses

June

1999

June

1999

January

2000

Other

June

1999

June

1999

Minnesota

New York

Idaho

Wisconsin

Illinois

California

Sh. sonnei

Norwalk-like

virus

Norwalk-like

virus

Norwalk-like

virus

Unknown

Unknown

25

168

25

9

25

23

The only shared exposure among the affected persons was

swimming in a particular area of a public beach. Seventeen

persons from >5 families who separately attended the beach

on the same day became ill; these persons did not all attend

the beach together and did not consume the same food products at the beach. Eight other persons, who were identified

through routine surveillance, also reported swimming at the

beach on the date in question. Water samples collected

>2 days after the implicated day did not test positive for

Shigella organisms. Because of the substantial number of children swimming at the lake, a fecal accident was the likely

source of contamination.

The outbreak was associated with swimming in shallow water

at a freshwater lake. Feces had been removed from the lake

that day by lifeguards.

The outbreak occurred at a resort and water park. The pool

implicated in the investigation was untreated. The source of

the pool’s water was a natural hot springs that was high in

mineral content and was not chlorinated or filtered. The

investigators noted that geothermal pools used for swimming are not required to be regulated by public health officials in that locale. The same pool had been implicated in a

previous outbreak of Norwalk-like virus in June 1996.

A motel pool was linked to the outbreak. The affected persons had attended a party where diapered infants were in the

water; they became ill in <48 hours after attending the event.

Stool specimens collected from these persons tested positive

for Norwalk-like virus by reverse-transcriptase polymerase

chain reaction and were negative for enteric bacteria.

Persons reported gastrointestinal illness after swimming in a

community lake. A septic system failure had occurred,

resulting in sewage contamination of the lake. Tests of the

lake water on >2 dates before and after the first case was

reported were all positive for fecal coliforms.

An outbreak of suspected viral etiology occurred among persons who attended three separate pool parties at an apartment complex. Initially, the outbreak was reported as a

possible foodborne outbreak, but no food items had been
42 MMWR November 22, 2002

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

August

1999

September

1999

Florida

Texas

Sh. sonnei and

Cr. parvum

Unknown

38

12

shared among the persons who had attended the three parties. Moreover, persons who only ate and did not swim in

the pool did not report illness. Stool specimens collected

from two persons tested negative for bacterial and parasitic

pathogens. No indication was provided that viral testing was

done. The health department conducted a physical inspection of the pool and examined pool maintenance records.

No water testing was performed by the health department,

nor were pool maintenance records available for the dates

immediately after the day of exposure, although reported

chlorine levels seemed adequate. However, swimmers

reported that on the day in question, the pool was overcrowded and that toddlers were swimming in the pool.

The outbreak occurred among persons who visited a beach

park, and it was attributed to both Sh. sonnei and Cr. parvum.

Illness was epidemiologically linked to playing in an interactive fountain at the park, ingesting water, and consuming

food and beverages at the fountain. The fountain’s recirculation and disinfection systems were not approved by the

health department and were inadequate or not completely

operational at the time of its use. Samples of the fountain

water tested positive for coliforms but did not test positive

for fecal coliforms. Nevertheless, the cause of the outbreak

was determined to be the fountain, which was closed until

the health department’s concerns could be remedied.§

Persons reported symptoms that included exhaustion, sore

muscles, headache, chills, and fever after attending a conference at a Texas guest ranch. One woman reported a miscarriage during her illness. Exposure to a hot tub, defined as

either immersion or being near the hot tub, was associated

with illness. Although clinical specimens (urine, blood, sputum, and throat swabs) were tested for organisms, including

Leg. pneumophila serogroups 1 and 6, influenza virus, parainfluenza virus, and adenovirus, no infectious agent was identified. No testing for biologic or chemical agents was

performed on water samples because the hot tub had already

been drained, refilled, and hyperchlorinated before the

environmental investigation.

§CDC. Outbreak of gastroenteritis associated with an interactive water fountain at a beachside park—Florida, 1999. MMWR 2000;49:565–8.
Vol. 51 / SS-8 Surveillance Summaries 43

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

February

2000

March

2000

May

2000

July

2000

July

2000

August

2000

Vermont

Maine

Florida

Maine

Florida

Florida

Bromine

P. aeruginosa

Unknown

Unknown

Unknown

Unknown

3

11

2

32

4

9

Chemical keratitis resulted from exposure to bromine in a

hotel swimming pool. Bromine levels were >5 ppm (acceptable bromine levels are 1–3 ppm), and the pH level was >8.5.

Patrons that spent time with their heads underwater with

their eyes open were affected.

An outbreak of dermatitis affected persons who had stayed

at a hotel during a sports tournament. These persons

reported having a rash that was accompanied by other symptoms, including ear infection, cough, headache, and joint

pain. P. aeruginosa was isolated from water samples from

both the pool and hot tub. The investigator also indicated

that disinfection might have been hindered by a high number

of swimmers and the addition of water to the leaking pool.

Persons became ill after swimming in a lake that was not

licensed as a bathing area and had signs posted indicating

that the area was unsafe for swimming. No water testing

results were available before or after the incident. The lake

had been closed for swimming for years, and routine samples

had not been collected.

Swimming at a beach in a campground was epidemiologically implicated in an outbreak of gastrointestinal illness.

Affected persons reported a combination of symptoms,

including diarrhea, vomiting, nausea, cramps, and headache

that lasted 5–48 days. Only one stool specimen was collected, which tested negative for bacterial pathogens; therefore, the outbreak was of suspected viral etiology. However,

no tests for parasitic organisms were reported. The environmental assessment and interviews indicated that the presence of diapered children, a heavy bather load, and warm

water temperatures were contributing factors to the outbreak.

Water samples tested negative for coliforms.

Affected persons reported swimming in a freshwater spring

that had a history of inadequate water quality. Water samples

from the spring’s swimming areas were positive for total and

fecal coliforms on multiple dates. Drinking water at this

facility was also tested but was negative for coliforms.

A motel pool that was cloudy and dirty at the time of exposure was implicated. Persons who swam in the pool and did

not share any other common exposure became ill with gastroenteritis. Disinfectant residuals and operation of the fil-
44 MMWR November 22, 2002

State

where Suspected Number

Outbreak outbreak or confirmed of persons

date(s) occurred etiologic agent affected Case description

October

2000

Alaska P. aeruginosa 29

tration system at the time of the investigation were deficient.

Problems had also occurred with the equipment used for

adjusting pH.

In an outbreak of dermatitis, the median number of persons

in the implicated hotel pool and hot tub was greater than

the maximal bather loads permitted. The maximum bather

load for the pool was nine persons, and for the hot tub, six

persons. On the basis of interviews, the median numbers of

persons were determined to be 12 (range: 4–20) in the pool

and 10 (range: 3–20) in the hot tub. The pool and hot tub

were on separate filtration systems. Sand from the pool

filter and water from the filter both tested positive for

P. aeruginosa. The filtration system was suspected as having

malfunctioned sometime during the day of exposure and

had been unable to maintain adequate levels of disinfection

to accommodate the excessive bather load.
Vol. 51 / SS-8 Surveillance Summaries 45

Glossary

Action level

Back-siphonage

Boil-water advisory

Cercarial dermatitis

Class

Coagulation

Coliforms

Community water

system

Contact time

Cross-connection

Cyst

Disinfection

by-products

Distribution system

Excystation

Fecal coliforms

Filter backwash

Filtration

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.

A reversal of the normal flow of water or other liquid caused by a negative-pressure gradient

(e.g., within a water system).

A statement to the public advising that tap water must be boiled before drinking it.

Dermatitis caused by contact with the cercariae (larval stage) of certain species of schistosomes

whose normal hosts are birds and nonhuman mammals.

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).

The process of adding chemicals to water to destabilize charges on naturally occurring particles

to facilitate their subsequent aggregation and removal by flocculation or filtration.

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).

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.

The length of time water is exposed to a disinfectant (e.g., chlorine contact time).

Any actual or potential connection between a drinking water supply and a possible source of

contamination or pollution (e.g., a wastewater line).

The infectious stage of Giardia intestinalis and certain other protozoan parasites that have protective walls that facilitate their survival in water and other environments.

Chemicals formed in water through reactions between organic matter and disinfectants.

Water pipes, storage reservoirs, tanks, and other means used to deliver drinking water to consumers or store it before delivery.

The release of the internal (i.e., encysted) contents (e.g., trophozoites or sporozoites) from cysts

or oocysts.

Coliforms that grow and produce gas at 112.1o

F (44.5oC) within 24 hours.

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

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).
46 MMWR November 22, 2002

Finished water

Flocculation

Free, residual chlorine

level

Groundwater system

Groundwater under

the direct influence

of surface water

Heterotrophic

microflora

Infant water

Individual (or private)

water system

Maximumcontaminant level

Nephelometric

turbidity units

Noncommunity water

system

Nontransient

noncommunity

water systems

Oocyst

Public water system

Raw water

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

The water-treatment process after coagulation that uses gentle stirring to cause suspended particles to form larger, aggregated masses (floc). The aggregates are removed from the water by a

separation process (e.g., sedimentation, flotation, or filtration).

The concentration of chlorine in water that is not combined with other constituents, thus serving as an effective disinfectant.

A system that uses water extracted from the ground (i.e., a well or spring).

Any water beneath the surface of the ground with substantial occurrence of insects or other

macrooganisms, algae, or large-diameter pathogens (e.g., Giardia intestinalis or — for subpart H

systems serving >10,0000 persons only — Cryptosporidium parvum, or substantial and relatively

rapid shifts in water characteristics (e.g., turbidity, temperature, conductivity, or pH that closely

correlate to climatological or surface water conditions. Direct influence must be determined for

individual sources in accordance with criteria established by the state. The state determination of

direct influence might be based on site-specific measurements of water quality or documentation

of well construction characteristics and geology with field evaluation.

Microorganisms that use organic material for energy and growth.

Bottled waters that are marketed for direct consumption by infants or use in mixing with infant

formula.

A water system not owned or operated by a water utility and that serves <15 residences or farms

not having access to a public water system.

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

user of a public water system.

The units in which the turbidity of a sample of water is measured when the degree to which light

is scattered is assessed with a nephelometric turbidimeter.

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, 2) has >15 service connections or serves an average of >25

persons, and 3) is not a community water system.

Public water systems that serve >25 of the same persons for >6 months/year (e.g., a factory or

school).

The infectious stage of Cryptosporidium parvum and certain other coccidian parasites with a

protective wall that facilitates survival in water and other environments.

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.

Surface water or groundwater that has not been treated in any way.
Vol. 51 / SS-8 Surveillance Summaries 47

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.

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

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

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

group of closely related bacteria that are usually free-living in the environment, but are also

normally present in water contaminated with human and animal feces. With certain exceptions,

they do not cause disease. Specifically, coliforms are used as a screen for fecal contamination as

well as to determine the efficiency of treatment and the integrity of the water distribution system. The presence of total coliforms in drinking water indicates that the system is either fecally

contaminated or vulnerable to fecal contamination.

Public water systems that regularly serve >25 of the same persons for >6 months/year (e.g.,

highway rest stations, restaurants, and parks with their own public water systems).

The quality (e.g., of water) of having suspended matter (e.g., clay, silt, or plankton) that results

in loss of clarity or transparency.

Surface water or groundwater that has not been treated in any way (also called raw water).

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.

A water provider that distributes drinking water to a community through a network of pipes.

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.

A program to protect a watershed from contamination or pollution.

Reverse osmosis

Source water

Surface water

Total coliforms

Transient

non-community

water systems

Turbidity

Untreated water

Water quality

indicator

Water utility

Watershed

Watershed-control

program
48 MMWR November 22, 2002
All MMWR references are available on the Internet at http://www.cdc.gov/mmwr. Use the search function to find specific articles.

——————

Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health

and Human Services.

——————

References to non-CDC sites on the Internet are provided as a service to MMWR readers and do not constitute or imply endorsement of

these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the

content of these sites. URL addresses listed in MMWR were current as of the date of publication.
MMWR

The Morbidity and Mortality Weekly Report (MMWR) series is prepared by the Centers for Disease Control and Prevention (CDC) and

is available free of charge in electronic format and on a paid subscription basis for paper copy. To receive an electronic copy each week, send

an e-mail message to listserv@listserv.cdc.gov. The body content should read SUBscribe mmwr-toc. Electronic copy also is available from

CDC’s Internet server at http://www.cdc.gov/mmwr or from CDC’s file transfer protocol server at ftp://ftp.cdc.gov/pub/publications/mmwr. To

subscribe for paper copy, contact Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402; telephone

202-512-1800.

Data in the weekly MMWR are provisional, based on weekly reports to CDC by state health departments. The reporting week

concludes at close of business on Friday; compiled data on a national basis are officially released to the public on the following Friday.

Address inquiries about the MMWR series, including material to be considered for publication, to Editor, MMWR Series, Mailstop C-08,

CDC, 1600 Clifton Rd., N.E., Atlanta, GA 30333; telephone 888-232-3228.

All material in the MMWR series is in the public domain and may be used and reprinted without permission; however, citation of the

source is appreciated.

✩U.S. Government Printing Office: 2003-533-155/69070 Region IV