Inside: Continuing Medical Education for U.S. Physicians and Nurses

Surveillance for Waterborne-Disease

Outbreaks — United States, 1997–1998

U.S. DEPARTMENT OF HEALTH & HUMAN SERVICES

Centers for Disease Control and Prevention (CDC)

Atlanta, GA 30333

May 26, 2000 / Vol. 49 / No. SS-4

CDC

Surveillance

Summaries
2 MMWR March xx, 2000

Centers for Disease Control and Prevention .................. Jeffrey P. Koplan, M.D., M.P.H.

Director

The production of this report as an MMWR serial publication was coordinated in

Epidemiology Program Office .......................................... Barbara R. Holloway, M.P.H.

Acting Director

Office of Scientific and Health Communications ........................ John W. Ward, M.D.

Director

Editor, MMWR Series

CDC Surveillance Summaries ...................................... Suzanne M. Hewitt, M.P.A.

Managing Editor

....................................................................................................... Amanda Crowell

Project Editor

.................................................................................................... Beverly J. Holland

Visual Information Specialist

Michele D. Renshaw

Erica R. Shaver

 Information Technology Specialists

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.

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Vol. 49 / No. SS-4 MMWR i

Contents

Reports Published in CDC Surveillance Summaries

Since January 1, 1990 ................................................................................ ii

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

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

Methods ............................................................................................................. 5

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

Discussion ....................................................................................................... 12

Conclusion ...................................................................................................... 18

References ....................................................................................................... 19

State and Territorial Epidemiologists and

Laboratory Directors ....................................................... Inside Back Cover
ii MMWR May 26, 2000

*Abbreviations

ATSDR Agency for Toxic Substances and Disease Registry

CIO Centers/Institute/Offices

EPO Epidemiology Program Office

IHPO International Health Program Office

NCCDPHP National Center for Chronic Disease Prevention and Health Promotion

NCEH National Center for Environmental Health

NCEHIC National Center for Environmental Health and Injury Control

NCHSTP National Center for HIV, STD, and TB Prevention

NCID National Center for Infectious Diseases

NCIPC National Center for Injury Prevention and Control

NCPS National Center for Prevention Services

NIOSH National Institute for Occupational Safety and Health

NIP National Immunization Program

Reports Published in CDC Surveillance Summaries Since January 1, 1990

Responsible

Subject CIO/Agency* Most Recent Report

Abortion NCCDPHP 1999; Vol. 48, No. SS-4

Aging

Health Risks NCCDPHP 1999; Vol. 48, No. SS-8

Health-Care Services NCCDPHP/NIP 1999; Vol. 48, No. SS-8

Health-Related Quality of Life NCEH/NCCDPHP 1999; Vol. 48, No. SS-8

Injuries and Violence NCIPC/NCCDPHP 1999; Vol. 48, No. SS-8

Morbidity and Mortality NCHS/NCCDPHP 1999; Vol. 48, No. SS-8

AIDS/HIV

AIDS-Defining Opportunistic Illnesses NCHSTP/NCID 1999; Vol. 48, No. SS-2

Among Black and Hispanic Children

and Women of Childbearing Age NCEHIC 1990; Vol. 39, No. SS-3

Asthma NCEH 1998; Vol. 47, No. SS-1

Behavioral Risk Factors NCCDPHP 2000; Vol. 49, No. SS-2

Birth Defects

Birth Defects Monitoring Program

(see also Malformations) NCEH 1993; Vol. 42, No. SS-1

Contribution of Birth Defects to Infant Mortality

Among Minority Groups NCEHIC 1990; Vol. 39, No. SS-3

Breast and Cervical Cancer NCCDPHP 1999; Vol. 48, No. SS-6

Cardiovascular Disease EPO/NCCDPHP 1998; Vol. 47, No. SS-5

Chancroid NCPS 1992; Vol. 41, No. SS-3

Chlamydia NCPS 1993; Vol. 42, No. SS-3

Cholera NCID 1992; Vol. 41, No. SS-1

Chronic Fatigue Syndrome NCID 1997; Vol. 46, No. SS-2

Contraception Practices NCCDPHP 1992; Vol. 41, No. SS-4

Cytomegalovirus Disease, Congenital NCID 1992; Vol. 41, No. SS-2

Dengue NCID 1994; Vol. 43, No. SS-2

Developmental Disabilities NCEH 1996; Vol. 45, No. SS-2

Diabetes Mellitus NCCDPHP 1993; Vol. 42, No. SS-2

Dracunculiasis NCID 1992; Vol. 41, No. SS-1

Ectopic Pregnancy NCCDPHP 1993; Vol. 42, No. SS-6

Elderly, Hospitalizations Among NCCDPHP 1991; Vol. 40, No. SS-1

Escherichia coli O157 NCID 1991; Vol. 40, No. SS-1

Evacuation Camps EPO 1992; Vol. 41, No. SS-4

Family Planning Services at Title X Clinics NCCDPHP 1995; Vol. 44, No. SS-2

Food Safety NCID 1998; Vol. 47, No. SS-4

Foodborne-Disease Outbreaks NCID 2000; Vol. 49, No. SS-1

Gonorrhea and Syphilis, Teenagers NCPS 1993; Vol. 42, No. SS-3

Hazardous Substances Emergency Events ATSDR 1994; Vol. 43, No. SS-2

Health Surveillance Systems IHPO 1992; Vol. 41, No. SS-4
Vol. 49 / No. SS-4 MMWR iii

Reports Published in CDC Surveillance Summaries Since January 1, 1990 — Continued

Responsible

Subject CIO/Agency* Most Recent Report

Homicide NCEHIC 1992; Vol. 41, No. SS-3

Hysterectomy NCCDPHP 1997; Vol. 46, No. SS-4

Infant Mortality (see also National Infant Mortality;

Birth Defects; Postneonatal Mortality) NCEHIC 1990; Vol. 39, No. SS-3

Influenza NCID 2000; Vol. 49, No. SS-3

Injury

Head and Neck NCIPC 1993; Vol. 42, No. SS-5

In Developing Countries NCEHIC 1992; Vol. 41, No. SS-1

Lead Poisoning, Childhood NCEHIC 1990; Vol. 39, No. SS-4

Low Birth Weight NCCDPHP 1990; Vol. 39, No. SS-3

Lyme Disease NCID 2000; Vol. 49, No. SS-3

Malaria NCID 1999; Vol. 48, No. SS-1

Measles NCPS 1992; Vol. 41, No. SS-6

Meningococcal Disease NCID 1993; Vol. 42, No. SS-2

Mumps NIP 1995; Vol. 44, No. SS-3

Neisseria gonorrhoeae, Antimicrobial Resistance in NCPS 1993; Vol. 42, No. SS-3

Neural Tube Defects NCEH 1995; Vol. 44, No. SS-4

Occupational Injuries/Disease

Asthma NIOSH 1999; Vol. 48, No. SS-3

Silicosis NIOSH 1997; Vol. 46, No. SS-1

Parasites, Intestinal NCID 1991; Vol. 40, No. SS-4

Pediatric Nutrition NCCDPHP 1992; Vol. 41, No. SS-7

Pertussis NCPS 1992; Vol. 41, No. SS-8

Poliomyelitis NCPS 1992; Vol. 41, No. SS-1

Postneonatal Mortality NCCDPHP 1998; Vol. 47, No. SS-2

Pregnancy

Pregnancy Nutrition NCCDPHP 1992; Vol. 41, No. SS-7

Pregnancy-Related Mortality NCCDPHP 1997; Vol. 46, No. SS-4

Pregnancy Risk Assessment

Monitoring System (PRAMS) NCCDPHP 1999; Vol. 48, No. SS-5

Pregnancy, Teenage NCCDPHP 1993; Vol. 42, No. SS-6

Racial/Ethnic Minority Groups Various 1990; Vol. 39, No. SS-3

Respiratory Disease NCEHIC 1992; Vol. 41, No. SS-4

Rotavirus NCID 1992; Vol. 41, No. SS-3

School Health Education Profiles NCCDPHP 1998; Vol. 47, No. SS-4

Sexually Transmitted Diseases in Italy NCPS 1992; Vol. 41, No. SS-1

Smoking NCCDPHP 1990; Vol. 39, No. SS-3

Smoking-Attributable Mortality NCCDPHP 1994; Vol. 43, No. SS-1

Tobacco-Control Laws, State NCCDPHP 1999; Vol. 48, No. SS-3

Tobacco-Use Behaviors NCCDPHP 1994; Vol. 43, No. SS-3

Spina Bifida NCEH 1996; Vol. 45, No. SS-2

Streptococcal Disease (Group B) NCID 1992; Vol. 41, No. SS-6

Syphilis, Congenital NCPS 1993; Vol. 42, No. SS-6

Syphilis, Primary and Secondary NCPS 1993; Vol. 42, No. SS-3

Tetanus NIP 1998; Vol. 47, No. SS-2

Trichinosis NCID 1991; Vol. 40, No. SS-3

Tuberculosis NCPS 1991; Vol. 40, No. SS-3

Waterborne-Disease Outbreaks NCID 2000; Vol. 49, No. SS-4

Years of Potential Life Lost EPO 1992; Vol. 41, No. SS-6

Youth Risk Behaviors NCCDPHP 1998; Vol. 47, No. SS-3

College Students NCCDPHP 1997; Vol. 46, No. SS-6

National Alternative High Schools NCCDPHP 1999; Vol. 48, No. SS-7
iv MMWR May 26, 2000
Vol. 49 / No. SS-4 MMWR 1

Surveillance for Waterborne-Disease Outbreaks —

United States, 1997–1998

Rachel S. Barwick, M.S., Ph.D.1,2

Deborah A. Levy, Ph.D., M.P.H.2

Gunther F. Craun, M.P.H.3

Michael J. Beach, Ph.D.2

Rebecca L. Calderon, Ph.D., M.P.H.4

1Epidemic Intelligence Service, Epidemiology Program Office, CDC

2Division of Parasitic Diseases, National Center for Infectious Diseases, CDC

3Gunther F. Craun & Associates, Staunton, Virginia

4Human Studies Division, National Health and Environmental Effects

Laboratory, U.S. Environmental Protection Agency

Abstract

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

(EPA) have maintained a collaborative surveillance system for collecting and

periodically reporting data relating to occurrences and causes of waterborne-disease

outbreaks (WBDOs).

Reporting Period Covered: This summary includes data from January 1997 through

December 1998 and a previously unreported outbreak in 1996.

Description of the System: The surveillance system includes data regarding 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.

Results: During 1997–1998, a total of 13 states reported 17 outbreaks associated with

drinking water. These outbreaks caused an estimated 2,038 persons to become ill. No

deaths were reported. The microbe or chemical that caused the outbreak was identified

for 12 (70.6%) of the 17 outbreaks; 15 (88.2%) were linked to groundwater sources.

Thirty-two outbreaks from 18 states were attributed to recreational water exposure

and affected an estimated 2,128 persons. Eighteen (56.3%) of the 32 were outbreaks of

gastroenteritis, and 4 (12.5%) were single cases of primary amebic meningoencephalitis caused by Naegleria fowleri, all of which were fatal. The etiologic agent was

identified for 29 (90.6%) of the 32 outbreaks, with one death associated with an

Escherichia coli O157:H7 outbreak. Ten (55.6%) of the 18 gastroenteritis outbreaks

were associated with treated pools or ornamental fountains. Of the eight outbreaks of

dermatitis, seven (87.5%) were associated with hot tubs, pools, or springs.

Interpretation: Drinking water outbreaks associated with surface water decreased

from 31.8% during 1995–1996 to 11.8% during 1997–1998. This reduction could be

caused by efforts by the drinking water industry (e.g., Partnership for Safe Water),

efforts by public health officials to improve drinking water quality, and improved water

treatment after the implementation of EPA’s Surface Water Treatment Rule. In contrast,

the proportion of outbreaks associated with systems supplied by a groundwater source
2 MMWR May 26, 2000

increased from 59.1% (i.e., 13) during 1995–1996 to 88.2% (i.e., 15) during 1997–1998.

Outbreaks caused by parasites increased for both drinking and recreational water. All

outbreaks of gastroenteritis attributed to parasites in recreational water were caused

by Cryptosporidium, 90% occurred in treated water venues (e.g., swimming pools and

decorative fountains), and fecal accidents were usually suspected. The data in this

surveillance summary probably underestimate the true incidence of WBDOs because

not all WBDOs are recognized, investigated, and reported to CDC or EPA.

Actions Taken: To estimate the national prevalence of waterborne disease associated

with drinking water, CDC and EPA are conducting a series of epidemiologic studies to

better quantify the level of waterborne disease associated with drinking water in

nonoutbreak conditions. The Information Collection Rule implemented by EPA in

collaboration with the drinking water industry helped quantify the level of pathogens in

surface water. Efforts by CDC to address recreational water outbreaks have included

meetings with the recreational water industry, focus groups to educate parents on

prevention of waterborne disease transmission in recreational water settings, and

publications with guidelines for parents and pool operators.

INTRODUCTION

Since 1920, national statistics on outbreaks associated with drinking water have been

available (1 ). Since 1971, CDC, the U.S. Environmental Protection Agency (EPA), and the

Council of State and Territorial Epidemiologists have maintained a collaborative surveillance system of the occurrences and causes of waterborne-disease outbreaks (WBDOs)

(2–5 ). This surveillance system includes data regarding outbreaks associated with drinking water and recreational water. This summary includes data for 1997 and 1998 and for

one previously unreported outbreak in 1996.

The goals of the waterborne-disease surveillance efforts of CDC and EPA are to a)

characterize the epidemiology of WBDOs; b) identify the etiologic agents that caused

WBDOs and determine why the outbreaks occurred; c) train public health personnel to

detect and investigate WBDOs; and d) collaborate with local, state, federal, and international agencies on initiatives to prevent waterborne diseases. The data gathered through

this surveillance system are useful for identifying major deficiencies in providing safe

drinking water and recreational water. Surveillance information also influences research

priorities and can lead to improved water-quality regulations.

BACKGROUND

EPA Regulations

Drinking Water

Public water systems are regulated under the Safe Drinking Water Act (SDWA) of

1974, which was amended in 1986 and 1996 (6–8 ). The 1996 amendments required EPA

to publish every 5 years a list of contaminants known or anticipated to occur in public

water systems and possibly needing regulation. The first list, called the drinking water

Contaminant Candidate List, was published March 2, 1998, and included 10 microbial

contaminants (9 ). Microbial contamination is regulated under the Surface Water Treat-
Vol. 49 / No. SS-4 MMWR 3

ment Rule (SWTR) of 1989 and the Total Coliform Rule (TCR) of 1989 (10–12 ). Additional

regulations are being developed.

Under TCR, all public water systems are required to routinely monitor their tap water

for total coliforms. The presence of total coliforms in drinking water indicates that the

system is either fecally contaminated or vulnerable to fecal contamination. A system

that collects 40 samples per month (generally, systems that serve >33,000 persons)

violates the Maximum Contaminant Level (MCL) if >5.0% of the samples (routine and

repeat samples) collected during each month are total coliform-positive. A system that

collects <40 samples per month violates MCL if two samples (routine and repeat samples)

during the month are total coliform-positive. If a system has a total coliform-positive

sample, then a) that sample must be tested for the presence of fecal coliforms or Escherichia coli, and b) three repeat samples must be collected (four, if the system collects 1

routine sample per month) within 24 hours and analyzed for total coliforms (then, if

positive, analyzed for fecal coliforms or E. coli ). In addition, approximately five 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 1 month, and one of these samples is also fecal coliform-positive or E. coli-positive,

the system has an acute violation of MCL and must report to the public immediately. TCR

also requires a periodic sanitary survey to evaluate and document the capabilities of the

water system’s sources, treatment, storage, distribution network, operation and maintenance, and overall management to ensure safe drinking water.

SWTR covers all water systems that use surface water or groundwater under the

direct influence of surface water. SWTR is intended to protect against exposure to Giardia intestinalis, viruses, and Legionella, as well as many other pathogens. This rule requires that all such systems reduce the level of Giardia by 99.9% (three log reduction)

and viruses by 99.99% (four log reduction). All surface water systems must disinfect

their water. Most water systems also must filter their water unless they meet EPAspecified filter avoidance criteria that define high-quality source water. Specifically, SWTR

requires a) a 0.2 mg/L disinfectant residual entering the distribution system; b) maintenance of a detectable disinfectant residual in all parts of the distribution system; c) 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); no single NTU reading >5.0; and d) watershed protection,

redundant disinfection capability, and other requirements for unfiltered systems.

On December 16, 1998, EPA promulgated the Interim Enhanced Surface Water Treatment Rule (IESWTR) (13 ), which will provide additional protection against

Cryptosporidium parvum and other waterborne pathogens. IESWTR covers all public

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

water and serve 10,000 persons. Key provisions include:

• A two log C. parvum 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; no single NTU

reading >1.0).

• Individual filter turbidity monitoring provisions.
4 MMWR May 26, 2000

• Disinfection benchmark provisions to ensure continued levels of microbial

protection while facilities take the 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 C. parvum.

• Requirements for covers on new, finished water reservoirs.

• Sanitary surveys for all surface water systems regardless of size.

• A MCL goal of zero oocysts for C. parvum.

EPA also plans to propose a companion microbial regulation for surface water systems serving <10,000 persons, called the Long Term 1 Enhanced SWTR. This rule will be

proposed in Spring 2000.

The Ground Water Rule, which is being developed, will likely stress a multibarrier

approach to ensure public health protection for public groundwater systems. EPA has

identified five potential areas of importance — groundwater source protection, well and

distribution system integrity, distribution system protection, disinfection, and monitoring.

The Ground Water Rule is expected to be proposed in Spring 2000. Recent revisions to

the Underground Injection Control Regulations published December 7, 1999, could provide additional protection of groundwater from both chemical and microbial contamination from shallow wells, including cesspools (14 ).

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

(15 ), which required large water systems serving approximately 100,000 persons to

monitor for the presence of Cryptosporidium and Giardia, total culturable viruses, and

total and fecal coliforms or E. coli at least once a month for 18 months. The required

monitoring ended in December 1998, and data are undergoing analysis. The results

could provide information to facilitate development of the Long Term 2 Enhanced SWTR,

which is intended to protect against microbial risks and balance the health risks associated with disinfection byproducts.

Recreational Water

State and local governments have jurisdiction over recreational water. The operation, disinfection, and filtration of public swimming and wading pools are regulated by

state and local health departments and often vary from place to place. For fresh recreational waters (e.g., lakes, ponds), EPA has established a guideline for microbial water

quality that indicates that the monthly geometric mean must be 33/100 ml for enterococci or 126/100 ml for E. coli. However, states can have either more or less stringent

guidelines or regulations and can post warning signs to alert potential bathers until water

quality improves. When lakes become contaminated, several weeks or months can be

required for water quality conditions 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 (16 ).
Vol. 49 / No. SS-4 MMWR 5

METHODS

Sources of Data

State, territorial, and local public health agencies have the primary responsibility for

detecting and investigating WBDOs and voluntarily reporting them to CDC on a standard

form (CDC form 52.12). CDC annually requests reports from state and territorial epidemiologists or from persons designated as WBDO surveillance coordinators. When

needed, additional information regarding water quality and treatment is obtained from

the state’s drinking water agency.

Definition of Terms*

The unit of analysis for the WBDO surveillance system is an outbreak, not an individual case of a particular disease. Two criteria must be met for an event to be defined as

a WBDO. First, at least two persons must have experienced a similar illness after either

ingestion of drinking water or exposure to water used for recreational purposes. The

stipulation that at least two persons be ill 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 must implicate water as the probable source of the illness. For drinking water,

outbreaks caused by contamination of 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 (among persons exposed to contaminated water) and secondary

cases (among persons who became ill after contact with primary case-patients) 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 is used if the study population was sampled randomly or the estimated count was calculated by using the attack rate.

Public water systems — classified as either community or noncommunity water systems — regularly provide piped water for human consumption to 15 service connections or an average of 25 persons for 60 days/year. Public water systems are regulated

under SDWA. A community water system serves year-round residents of a community,

subdivision, or mobile home park that has 15 service connections or an average of 25

residents. There are two categories of noncommunity water systems — nontransient

and transient. Nontransient noncommunity water systems are public water systems that

serve 25 of the same persons for >6 months of the year (e.g., a factory or school).

Transient noncommunity water systems do not regularly serve 25 of the same persons

for >6 months of the year. Typical transient noncommunity water systems are highway

rest stations, restaurants, and parks with their own public water systems. The distinction

between these two types of systems is important when considering the potential health

effects associated with chronic low levels of exposure to certain chemicals (e.g., benzene). However, acute high-level exposure to chemicals or acute exposure to infectious

agents are of concern in both types of systems. Of the approximately 170,000 public

water systems in the United States, 115,000 (67.6%) are noncommunity systems, serving transients (95,000 systems) and nontransients (20,000); 55,000 (32.4%) are community systems (EPA Safe Drinking Water Information System database, unpublished data,

*Additional terms are defined in the glossary.
6 MMWR May 26, 2000

1998). Community water systems serve approximately 243 million persons in the United

States (91.0% of the U.S. population); approximately 24 million persons (9.0%) rely on

private or individual water systems, which are small systems that are not owned or

operated by a water utility and that serve <15 connections or <25 persons. In addition,

millions of persons use noncommunity systems while traveling or working.

Each drinking water system associated with a WBDO is classified as having one of the

deficiencies listed below. If more than one deficiency is noted on the outbreak report

form, the deficiency that most likely caused the outbreak is noted. The deficiency classifications are as follows:

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).

5 = Unknown or miscellaneous deficiency (e.g., contaminated bottled water).

Recreational waters include swimming pools, whirlpools, hot tubs, spas, water parks,

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.

Classification of Outbreaks

This surveillance system classifies WBDOs according to the strength of the evidence

implicating water (Table 1). The classification numbers (i.e., Classes I–IV) are based on the

epidemiologic and water-quality data provided on the outbreak report form. Epidemiologic data are weighted more heavily than water-quality data. Thus, although some

outbreaks without water-quality data were included in this summary, reports without

supporting epidemiologic data were excluded. Outbreaks of Pseudomonas dermatitis

and single cases of primary amebic meningoencephalitis or single cases of illness resulting from chemical poisoning are not classified according to this scheme.

A classification of I means that adequate epidemiologic and water-quality data were

reported but does not necessarily imply that the investigation was optimal. Classifications II–IV do not necessarily imply that the investigations were flawed; the circumstances of each outbreak differ, and not all outbreaks can or should be rigorously

investigated.

RESULTS

Outbreaks Associated with Drinking Water

During 1997–1998, a total of 13 states reported 17 outbreaks associated with drinking

water. Seven were reported for 1997 and 10 for 1998. Florida reported the most outbreaks (i.e., four). These outbreaks caused an estimated 2,038 persons to become ill. The

median outbreak size was 10 persons (range: 2–1,400). No deaths were attributed to
Vol. 49 / No. SS-4 MMWR 7

these outbreaks. Outbreaks were most common during the summer and fall months

(Figure 1). Fifteen (88.2%) of the 17 outbreaks occurred during May–October.

Seven (41.2%) of the 17 outbreaks were assigned to Class I based on epidemiologic

and water-quality data; none were Class II or Class IV, and 10 (58.8%) were Class III.

Outbreaks are listed by state (Tables 2 and 3) and are tabulated by the etiologic agent and

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

(Table 5).

Etiologic Agents

Ten (58.8%) of the 17 outbreaks were of known infectious etiology, 5 (29.4%) were of

unknown etiology, and 2 (11.8%) were attributed to chemical poisoning. Of the 10 outbreaks with known infectious etiology, 6 (60.0%) were caused by parasites and 4 (40.0%)

by bacteria (Figure 2).

Parasites. During 1997, two outbreaks were caused by Giardia, one in New York and

the other in Oregon. The outbreak of giardiasis in New York occurred during June, affected 50 persons, and was associated with a surface water supply that was chlorinated

but unfiltered. A beaver was found in a valve box near the reservoir, but no data were

provided on the presence of Giardia in the beaver. The outbreak at a campground in

Oregon also occurred during June, affected 100 persons, and was associated with drinking water from a noncommunity system that combined groundwater from an untreated

well and a chlorinated spring. Although rodents were suspected to have contaminated a

storage reservoir at a campground, no data were provided regarding Giardia in the

rodents. Two outbreaks of giardiasis occurred in Florida during 1998. In May, seven

persons from two households became ill after drinking water from an untreated groundwater source. In December, two persons became ill in a household with an untreated

groundwater system. Recent rainfall and possible flooding were suspected to have contaminated the well.

Two outbreaks were associated with Cryptosporidium. The first outbreak occurred at

a children’s group home in New Mexico where staff, residents, and visitors became ill

with cryptosporidiosis after drinking from spigots supplied by chlorinated well water. The

home was served by a community water system but also had an irrigation well with

several spigots on the grounds. Although the well water was not intended for drinking,

the spigots were not marked as nonpotable, and the well did not have a sanitary seal to

protect it from surface water drainage. In addition, several persons swam in a pool filled

with this well water, which could have contributed to the outbreak. In the second outbreak

of cryptosporidiosis, approximately 1,400 persons became ill and 23 were hospitalized in

Texas after >160,000 gallons of raw sewage spilled, flowed through underground fissures in a creek bed and into an aquifer located near five municipal utility district wells,

and contaminated four of the five wells. The spill was caused by a lightning storm that

shorted the controls of a sewage treatment plant. Although no deficiencies were observed in the treatment process of the well water, the treatment provided (chlorine

disinfection) would not be expected to kill Cryptosporidium.

Bacteria. Four outbreaks were caused by bacteria; three were attributed to E. coli

O157:H7 and one to Shigella sonnei. The first outbreak of E. coli O157:H7 occurred in

Wyoming, affected 157 persons, and was associated with a community water system

supplied by a spring and two wells. The water in this system was not treated, and the

outbreak could have resulted from fecal contamination by wildlife near the spring. A
8 MMWR May 26, 2000

second outbreak of E. coli O157:H7 in Illinois involved three persons who drank from an

untreated well located near a cattle pasture. E. coli O157:H7 was isolated from the well

water. The third outbreak of E. coli O157:H7 occurred in Washington at a trailer park and

was associated with a chlorinated groundwater supply. Approximately four persons

became ill, and one was hospitalized. The method of contamination could not be determined, but the water system was not in compliance with state and county regulations.

A cross-connection was blamed for an outbreak of S. sonnei that occurred in Minnesota at a local fair supplied by a community water system. The outbreak affected 83

persons, four of whom were hospitalized. Pulse-field gel electrophoresis (PFGE) subtyping

was used to identify the outbreak strain. Two foodborne outbreaks of S. sonnei occurred

earlier in 1998 in Minnesota at two restaurants, and the waterborne outbreak strain from

the fair matched the strain associated with the restaurant outbreaks. One person exposed to S. sonnei at one of the restaurant outbreaks reported attending the fair while ill.

Chemicals. Two outbreaks of copper poisoning were reported in Florida. In the first

outbreak, two persons became ill after consuming fruit drink made with tap water. Improper wiring and plumbing procedures caused leaching of copper from restaurant piping. After the outbreak, the owners of the restaurant replaced the copper tubing with

polyvinyl chloride (PVC) and replaced the check valve. In the second outbreak, elevated

levels of copper in tap water were associated with gastrointestinal illness among 35

persons in one community. A defective check valve and a power outage led to a malfunction at a water treatment facility, releasing high levels of sulfuric acid, which corroded the

pipes and allowed leaching of copper into the system.

Unidentified Etiologic Agent

The etiologic agent was not identified for five (29.4%) of the 17 WBDOs associated

with drinking water. The illnesses associated with at least four of the outbreaks had

incubation periods, durations, and symptom complexes consistent with viral syndromes.

Three outbreaks occurred during 1997 — one in Colorado, one in New Mexico, and one in

South Dakota. In Colorado, nine persons became ill after an extended family leased

recreational cabins for the summer. The cabins’ water system was supplied by a spring,

but the system’s chlorinator was not functioning at the time of the outbreak. No stool

specimens were available for laboratory diagnosis. In New Mexico, 123 persons became

ill with gastroenteritis after visiting a country club. The country club was supplied by a

groundwater source that was not chlorinated routinely. Before the outbreak, the club had

a history of problems, including sewage leaks and high coliform levels in the tap water.

Stool specimens were submitted for diagnostics, and 11 specimens were positive for E.

coli O86:H11. However, because E. coli O86:H11 is not a recognized pathogen and lacks

virulence markers, its role in the illness was not established. Although one specimen was

positive for Giardia, the median incubation period (20 hours) and duration of illness (2

days) were not consistent with giardiasis. In South Dakota, 16 persons at a camp became

ill with gastroenteritis associated with drinking tap water. In 1998, one outbreak of unknown etiology was reported in Montana when five persons became ill after drinking tap

water from an individual household supplied by well water treated with chlorine. One

person was hospitalized. In Ohio, 10 persons became ill after a temporary cross-connection in the water treatment plant and its offices occurred. Stool specimens were submitted for diagnostics, and 1 of 15 was positive for Blastocystis hominis and Endolimax

nana, suggesting exposure to feces.
Vol. 49 / No. SS-4 MMWR 9

Water-Quality Data

Information regarding the presence of coliform bacteria, pathogens, or chemical contaminants was available for 16 (94.1%) of the 17 reported outbreaks. Water samples

were tested for coliform bacteria during the investigation of 12 (70.6%) of the 17 outbreaks and were positive for total or fecal coliforms for 10 (83.3%) of the 12 outbreaks.

No information regarding the presence of coliforms was available for one outbreak of

undetermined etiology and two of four outbreaks caused by Giardia. However, in two

outbreaks of giardiasis, water samples were tested for Giardia cysts. One of the giardiasis outbreaks was associated with chlorinated, unfiltered surface water; 200 cysts/100 L

were found in a tap water sample. The second outbreak was associated with a chlorinated groundwater source, and 1.1 cysts/100 L were found in a sample of water collected

at a campsite. In two other outbreaks of giardiasis in Florida, water was not tested for

Giardia cysts, but coliforms were detected in one of the outbreaks. Both of these outbreaks were associated with untreated well water.

In one outbreak of cryptosporidiosis associated with chlorinated well water, tap water

samples were negative for coliforms, but fecal coliforms, total coliforms, and oocysts

were detected in the well water. In a second outbreak, samples from a chlorinated well

were positive for total and fecal coliforms, but oocysts were not detected.

Total coliforms were detected in tap water samples for all four of the bacterial outbreaks and four (80.0%) of the five outbreaks of unknown etiology. In the outbreak of

unknown etiology in New Mexico, which was caused by contamination within the water

distribution system, EPA used tissue culture techniques to detect the presence of an

enteric virus in a 150-gallon water sample from the well. Fecal coliforms were also

detected in two of the bacterial outbreaks and one of the outbreaks of unknown etiology.

In the outbreak of E. coli O157:H7 in Illinois, the organism was cultured from a water

sample from the untreated well.

Tap water was tested for copper levels in both copper poisoning outbreaks. In the

restaurant outbreak, 3.6 mg/L of copper was found in the tap water after leaching from

copper plumbing. In the second outbreak, copper levels of 33 mg/L and 138 mg/L and a

pH <6 were found in two water samples collected on the day that excess sulfuric acid was

inadvertantly added to the water system.

Water System and Water Source

Eight (47.1%) of the 17 WBDOs were associated with community systems, 5 (29.4%)

with noncommunity systems, and 4 (23.5%) with individual water systems (Tables 4 and

5). Only two (11.8%) of the outbreaks were associated with surface water systems.

Three (37.5%) of the eight outbreaks associated with community water systems were

caused by problems at water treatment plants, three (37.5%) were the result of problems in the water distribution systems and plumbing of individual facilities (e.g., offices,

schools, and restaurants), and two (25.0%) were associated with contaminated, untreated

groundwater.

All five of the outbreaks in noncommunity systems were associated with groundwater systems. Two (40.0%) of the five outbreaks were caused by contamination in the

distribution system. Interruption of chlorination was responsible for two outbreaks of

unknown etiology. Inadequate chlorination of a well water source (i.e., coliforms were

present in tap water) caused an outbreak of E. coli O157:H7.
10 MMWR May 26, 2000

All four outbreaks in individual water systems were associated with groundwater

systems. Outbreaks caused by Giardia, Cryptosporidium, and E. coli O157:H7 were

reported in untreated well water systems; an outbreak of unknown etiology was associated with inadequate chlorination of well water (i.e., coliforms were present in tap water).

Of the six protozoan outbreaks, five (83.3%) occurred in groundwater systems (four

used well water sources and one used both well and spring water sources). All four of the

outbreaks of bacterial etiology occurred in groundwater systems (three used well water

and one used both well and spring water). Four (75.0%) of the five outbreaks of unknown

etiology occurred in groundwater systems (three used well water and one spring water).

Outbreaks Associated with Recreational Water

During 1997–1998, a total of 18 states reported 32 outbreaks associated with recreational water (Tables 6–9). Seven outbreaks were reported for 1997 and 25 for 1998. The

states that reported the most outbreaks were Wisconsin (seven outbreaks) and Minnesota (four outbreaks). These 32 outbreaks caused illness in an estimated 2,128 persons.

The median outbreak size was 11 persons (range: 1–650).

All but 1 of the 18 outbreaks of gastroenteritis occurred during the summer (Figure 3).

The four cases of primary amebic meningoencephalitis also occurred during summer

months. Six (75%) of the eight outbreaks of dermatitis (i.e., rash) occurred during January or February.

Etiologic Agents

Twenty-nine (90.6%) of the 32 recreational water outbreaks were of known infectious

etiology (Tables 6–9). Nine (50.0%) of the 18 outbreaks of gastroenteritis were caused by

parasites, 4 (22.2%) by bacteria, 2 (11.1%) by viruses, and 3 (16.7%) were of unknown

etiology (Tables 6–9). There was one outbreak of Pontiac fever and one of leptospirosis.

Of the 32 recreational water outbreaks, 15 (46.9%) were associated with fresh water and

17 (53.1%) with treated water (Figure 4).

Parasites. All of the outbreaks of gastroenteritis caused by parasites were caused by

Cryptosporidium. One was associated with fresh water and eight with treated recreational water, either in pools or fountains (Figure 4).

One outbreak occurred in Pennsylvania, where eight persons became ill with

cryptosporidiosis after swimming in a lake at a state park; two persons were hospitalized.

The other eight outbreaks of cryptosporidiosis were associated with treated recreational

water. In Minnesota, 369 persons became ill after playing in a sprinkler fountain at a local

zoo (17 ). The fountain was originally designed as a decorative fountain. The water was

not intended for drinking but had become a popular interactive play area for children.

Water was sprayed through the air, drained through grates, collected, passed through a

sand filter, and chlorinated and recirculated. The original source of contamination was

unknown, but the fountain was a popular place for children to soak themselves during the

heat of the summer. Two other outbreaks of cryptosporidiosis occurred in Minnesota

during 1998, one at a swim club and the other at a community pool. The source of the

outbreak at the community pool was unknown, but the suspected source at the swim club

was a child with cryptosporidiosis who swam in the pool 7–10 days before the outbreak.

An outbreak occurred in Florida in a day care pool when seven persons became ill with

cryptosporidiosis. Although the source of the outbreak was unknown, there were reports

of babies in diapers swimming in the pool. In Oregon, 69 persons became ill with
Vol. 49 / No. SS-4 MMWR 11

cryptosporidiosis after swimming in a community pool. The source of the outbreak was

unknown although fecal contamination was suspected. Three outbreaks of

Cryptosporidium occurred in Wisconsin, all associated with public pools, and in all, the

suspected source was fecal accidents. One outbreak in Wisconsin involved three separate swimming pools with a total of 12 persons acquiring cryptosporidiosis. The source of

the outbreak was suspected to be a child, later diagnosed with Cryptosporidium, who had

a fecal accident in three community swimming pools on three successive days. Pool

operators were unaware of the accidents until the mother of the child reported them

2 weeks later.

In 1998, four cases of primary amebic meningoencephalitis were attributed to

Naegleria. All four of the infected children, who ranged in age from 3–14 years, died.

Infection was acquired when the children swam in a lake (two children), river (one child),

or canal (one child). Two of the cases were associated with exposure in Texas, one in

Florida, and one in Oklahoma.

Bacteria. Four (22.2%) of the 18 outbreaks of gastroenteritis were attributed to bacteria. Three of these outbreaks were caused by E. coli O157:H7, two in fresh water and

one in treated water (Figure 4). Eight persons attending a family reunion became ill in

Missouri after swimming at a lake resort. In an outbreak at a water park in Georgia, 26

persons became infected with E. coli O157:H7 (18 ). Seven of these case-patients developed hemolytic uremic syndrome and one died. A fecal accident in a children’s pool in the

water park was suspected to be the source of the outbreak. Low chlorine levels documented during that period could have been inadequate to inactivate the bacteria. In

Minnesota, five persons developed gastroenteritis caused by E. coli O157:H7 after swimming in a lake. One person was hospitalized. Nine persons became ill from S. sonnei in

Massachusetts. This outbreak was associated with a wading pool that included a sprinkler fountain. The system recirculated chlorine-treated water, and many diaper-aged

children were observed sitting in the wading pool.

An outbreak of leptospirosis occurred among competitors in a triathlon in Illinois

during 1998 (19 ). Three hundred seventy-five persons became ill after swimming in a

lake, 28 of whom were hospitalized, making this the largest outbreak of leptospirosis

ever reported in the United States. Wisconsin reported one outbreak of Pontiac fever

among 45 guests at a hotel. The source of exposure was linked to use of the hotel

whirlpool. The whirlpool log indicated adequate amounts of disinfectant in the whirlpool

during the time of exposure.

Other. After swimming at a public lake beach, 30 persons in Ohio and an estimated 18

persons in Wisconsin became ill with Norwalk-like virus (NLV). In both outbreaks, lake

water tested positive for fecal coliforms, but the source of the virus was not identified. In

the Ohio outbreak, latrines were located close to a stream that fed into the lake and were

considered a potential source of contamination. No agent could be identified for three

(16.7%) of the 18 outbreaks of gastroenteritis; all three were associated with lakes.

An estimated 127 persons were affected in eight outbreaks of dermatitis associated

with pools, hot tubs, springs, or lakes. All eight outbreaks had known or suspected infectious etiologies (Table 9). P. aeruginosa was confirmed as the etiologic agent for three

(42.9%) of the seven Pseudomonas outbreaks and was suspected in the other five,

based on the clinical syndromes. A Schistosoma species was the presumptive etiologic

agent of the one outbreak of swimmer’s itch because the clinical signs were consistent

with cercarial dermatitis.
12 MMWR May 26, 2000

Previously Unreported Outbreak

A previously unpublished NLV outbreak during 1996 was reported (Table 10). This

outbreak was associated with drinking tap water at an elementary school in Florida. An

estimated 594 persons, including students and staff, became ill with gastrointestinal

symptoms; no one was hospitalized. Investigation of the water supply system failed to

identify evidence of contamination or any event that could have resulted in contamination.

Outbreaks Not Classified as Waterborne-Disease Outbreaks

Outbreaks attributed to drinking water contaminated at the point of use, rather than

at the source or in the distribution system, are not classified as WBDOs. Although several

point-of-use outbreaks were reported to the WBDO surveillance system during 1997–

1998, these outbreaks are not included in this surveillance summary.

In 1997, a total of 11 residents and employees of a group home in Missouri became ill

with fever and upper respiratory symptoms associated with vaporizer and whirlpool use;

five persons were hospitalized. The following agents were isolated from patients:

P. aeruginosa, Serratia marcesens, Klebsiella pneumoniae, Citrobacter species,

Enterobacter aerogenes, E. cloacae, and P. alcaligenes. Evidence of P. aeruginosa and

E. cloacae also were found in the vaporizers and whirlpools. During 1998, an outbreak in

Missouri possibly was associated with contaminated ice. Four persons who consumed

ice from a restaurant storage bin became ill with gastroenteritis attributed to S. aureus.

In 1997, an outbreak of Campylobacter jejuni was reported among 106 guardsmen

of the Minnesota Army National Guard following a training exercise in Greece. The

source of the outbreak was bottled water consumed during international field exercises.

The water was bottled in Greece. Five additional outbreaks that occurred during 1997–

1998 were not included in this surveillance summary because of insufficient epidemiologic data to classify them as WBDOs (i.e., the outbreaks did not meet the criteria for

Classes I–IV).

DISCUSSION

General Considerations Regarding Surveillance Data

Waterborne-disease surveillance data are useful for evaluating the adequacy of approaches for providing safe drinking and recreational water. However, the data in this

surveillance summary probably underestimate the true incidence of WBDOs or the relative incidence of outbreaks caused by various etiologic agents. Not all WBDOs are recognized, investigated, and reported to CDC or EPA, and the extent to which WBDOs are

unrecognized and underreported is unknown. A national quick-response notification system through which public health officials and health-care providers could share provisional data on WBDOs would be useful.

The likelihood that individual cases of illness will be detected, epidemiologically linked,

and associated with water varies considerably among locales and is dependent on many

factors. These factors include a) public awareness, b) the likelihood that persons who are

ill will consult the same rather than different health-care providers, c) availability and

extent of laboratory testing, d) local requirements for reporting cases of particular dis-
Vol. 49 / No. SS-4 MMWR 13

eases, and e) the surveillance and investigative activities of state and local health and

environmental agencies. Therefore, the states that report the most outbreaks might not

be those where the most outbreaks occur. Recognition of WBDOs also is dependent on

certain outbreak characteristics; outbreaks involving serious illness are most likely to

receive the attention of health authorities. Outbreaks of acute diseases, particularly

those characterized by a short incubation period, are more readily identified than those

associated with disease from chronic, low-level exposure to an agent (e.g., some chemicals). Recreational water outbreaks that result from persons congregating in one venue,

then dispersing into a wide area could be difficult to document. Outbreaks associated

with community water systems are more likely to be recognized than those associated

with noncommunity systems because the latter serve mostly nonresidential areas and

transient populations. Outbreaks associated with individual systems are the most likely

to be underreported because they generally involve few persons.

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 obtained.

The practices of investigators’ laboratories can also influence whether the etiologic agent

is identified. For example, diarrheal stool specimens generally are examined for bacterial pathogens, but not for viruses. In many laboratories, testing for the parasite

Cryptosporidium is conducted only if requested and is not included in routine stool examinations for ova and parasites (20 ). The water-quality data collected vary widely

among outbreak investigations, depending on such factors as available fiscal, investigative, and laboratory resources. Furthermore, a few large outbreaks can substantially

alter the relative proportion of cases of waterborne disease attributed to a particular

agent. Finally, the number of reported cases is generally an approximate figure, and the

method and accuracy of the approximation vary among outbreaks.

Outbreaks Associated with Drinking Water

The number of outbreaks reported during 1997 (i.e., 7) and 1998 (i.e., 10) is comparable with those reported during 1996 (i.e., 6). However, the number of outbreaks reported for these 3 years is lower than those reported for any 2-year period since 1971.

WBDO reports peaked during 1979–1983 (Figures 5–6). The increase and subsequent

decrease in the number of reports might reflect, at least in part, changes in surveillance

activities or be a reporting artifact (21 ). The recent decrease in the number of outbreaks

reported since 1996 could also be caused by improved implementation of water treatment regulations (e.g., SWTR), increased efforts by many water utilities to produce drinking water substantially better than EPA standards require, and efforts by public health

officials to improve drinking water quality.

Drinking water outbreaks associated with surface water decreased from 31.8% (i.e., 7)

during 1995–1996 to 11.8% during 1997–1998, when only two outbreaks were attributed

to surface water supplies. One was an outbreak of giardiasis and the other was of unknown etiology. The outbreak of giardiasis that occurred in New York during 1997 was

associated with a surface water supply that was chlorinated but not filtered. Outbreaks

associated with surface water demonstrate the importance of requiring water systems

to provide an adequate chlorine concentration and contact time (as specified by SWTR)

to inactivate Giardia and other organisms that are relatively chlorine-resistant, especially if the surface water is unfiltered (22 ). Giardia can be inactivated by disinfection

without filtration, but only if stringent conditions are consistently maintained. Providing
14 MMWR May 26, 2000

both filtration and chlorination is an example of using multiple barriers to protect water

supplies.

The number of outbreaks associated with systems supplied by a groundwater source

(i.e., 15) increased from the 1995–1996 reporting period (i.e., 13), representing the largest proportion (88.2%) of such outbreaks since 1978, when outbreak source water was

first recorded (i.e., surface water versus groundwater). Of the 15 outbreaks associated

with groundwater during 1997–1998, a total of 10 (66.7%) were associated with a system

that had a treatment problem or distribution deficiency; 4 (26.7%) were associated with

systems that had untreated water; and 1 (6.67%) had an unknown problem. Groundwater is often not routinely disinfected and almost never filtered at the treatment plant.

Therefore, wells and springs must be protected from sources of contamination (e.g.,

surface runoff, septic tank drainage, and sewage discharges). EPA is developing a groundwater rule. Adequate and continuous disinfection of groundwater used for drinking water should be considered to reduce the occurrence of WBDOs caused by

chlorine-sensitive organisms, particularly for systems in which intermittent contamination of wells and springs is difficult to detect or prevent.

Three of the four outbreaks of Giardia were attributed to groundwater. Two involved

water from groundwater systems that were untreated except for ion exchange softening, whereas the third outbreak involved water disinfected with chlorine. Three of the

four outbreaks of unknown etiology associated with drinking water occurred in systems

using groundwater that experienced treatment deficiencies.

The outbreak in Texas during 1998 that was attributed to Cryptosporidium was associated with chlorinated wells located in limestone. Cryptosporidium is a smaller (4–6 μm)

protozoan parasite than Giardia and is >50-fold more resistant to chlorine. Because

Cryptosporidium is highly resistant to the chemicals typically used to treat drinking

water, the parasite must be physically removed by filtration. However, karst (limestone)

and fractured bedrock do not provide adequate natural filtration (23 ). Groundwater in

these types of geologic formations can be under the direct influence of surface water and

is more likely to be contaminated. Groundwater sources under the direct influence of

surface water are included in SWTR, and the water might need to be filtered as well as

disinfected.

All four drinking water outbreaks attributed to bacteria during this reporting period

were associated with groundwater. This has been the case for all reported bacterial

outbreaks since 1989. Three of the four outbreaks reported during this period were

associated with untreated or inadequately chlorinated well water. In two of the three

outbreaks, groundwater contamination was attributed to migration of fecal bacteria carried by surface water through the soil.

Although major advances have been made in detecting viruses in stool and environmental samples, and many outbreaks of acute gastrointestinal illness of unknown etiology (AGI) have epidemiologic and clinical characteristics consistent with viral etiology,

only two outbreaks caused by a viral agent have been reported to CDC since 1991.

Investigators are encouraged to submit clinical specimens for viral testing, either to CDC

or state laboratories that conduct these tests.

Two outbreaks of chemical poisoning were reported to CDC during 1997–1998, a

decrease from the number of outbreaks during 1995–1996 (i.e., 7). Both outbreaks were

caused by copper poisoning, but the outbreak in 1998 underscores that corrosive water

can cause leaching of metals from the plumbing and water distribution system. EPA
Vol. 49 / No. SS-4 MMWR 15

requires monitoring for copper (and lead) at the tap rather than at the treatment plant,

and EPA’s action level for copper is 1.3 mg/mL (24 ). The results of this monitoring are

used to determine whether treatment to control corrosion is needed or is being applied

properly.

Waterborne chemical poisonings are probably underreported to CDC. Several reasons could explain the low reporting rate, including the following:

• Most poisonings of this nature (e.g., those associated with the leaching of copper

from plumbing systems) probably occur in private residences, affect relatively

few persons, and might not come to the attention of public health officials.

• Exposure to chemicals via drinking water can a) cause illness that is difficult to

attribute to chemical intoxication or b) cause nonspecific symptoms that are

difficult to link to a specific chemical.

• The mechanisms for detecting waterborne chemical poisonings and reporting

them to the WBDO surveillance system are not as well-established as those for

WBDOs caused by infectious agents.

• Physicians might have difficulties recognizing and diagnosing chemical

poisonings.

Future efforts should be tailored to improving the sensitivity of surveillance activities,

the detection of associations between environmental releases or exposure incidents and

individual health events, and the assessment of the public health burden associated with

water-related chemical exposures. Physicians should also be educated to recognize and

diagnose poisonings caused by waterborne chemicals.

The relative proportion of outbreaks associated with various types of water systems

has remained fairly constant (Figure 6). However, the proportion of reported outbreaks

associated with community water systems that were attributed to problems at water

treatment plants, and thus affected entire communities, declined during 1989–1996 and

remained below the proportions for the 1989–1994 reporting periods (i.e., 72.7% for

1989–1990, 62.5% for 1991–1992, 57.1% for 1993–1994, 30.0% for 1995–1996, and 37.5%

for 1997–1998). This decrease could reflect improvements in water-treatment practices

and plant operations. During 1997–1998, three (37.5%) of the eight outbreaks in community water systems were caused by improper plumbing or cross-connections in the distribution system at individual facilities (e.g., a restaurant). This is a decrease from the

previous reporting period (i.e., 70.0%). These types of problems could be remedied by

effective cross-connection control regulations that require inspection and testing. However, monitoring, regulating, and standardizing the practices of the multitudinous individual facilities (e.g., offices, schools, and restaurants) in this country is a daunting task.

Outbreaks Associated with Recreational Water

The most frequently reported WBDOs caused by exposure to recreational water

were outbreaks of gastroenteritis. Although fewer outbreaks of gastroenteritis were

reported during 1997–1998 (i.e., 18) than during 1995–1996 (i.e., 22), this number was

higher than previous years (Figure 7). There has been a gradual increase in the number

of gastroenteritis outbreaks reported since 1989. This increase is not statistically significant (p value 0.18), and there is not enough evidence to determine if the increase
16 MMWR May 26, 2000

represents the beginning of a trend or a reporting artifact. The 15 recreational water

outbreaks reported in 1998 represent the largest number of outbreaks since 1989. Recreational water outbreaks of gastroenteritis reported during 1997–1998 accounted for

illness in >1,570 persons, compared with 2,038 persons affected by drinking water outbreaks reported during this same period.

Because swimming is essentially communal bathing, rinsing of soiled bodies and

overt fecal accidents cause fecal contamination of the water. Unintentional ingestion of

recreational water contaminated with pathogens can then lead to gastrointestinal illness, even in nonoutbreak settings (25,26 ). Fresh and marine waters are also subject to

other modes of contamination from point sources (i.e., sewage releases), watersheds

(runoff from agricultural and residential areas), and floods.

The number of outbreaks of gastroenteritis caused by parasites in recreational water

has been consistently 10 since 1989–1990 (i.e., zero for 1989–1990, 6 for 1991–1992, 10

for 1993–1994, 7 for 1995–1996, and 10 for 1997–1998). No outbreaks of gastroenteritis

caused by parasites were reported during 1989–1990, but that could be because little

routine diagnostic testing for Cryptosporidium occurred at that time. Of the gastrointestinal outbreaks attributed to parasites during 1997–1998, all were caused by

Cryptosporidium; 90% were associated with recreational use of treated water in venues

such as swimming pools and fountains, and human fecal accidents were suspected in

most of these outbreaks (Figure 4).

Because infection with Cryptosporidium can occur after swallowing as few as 10–

100 oocysts (27,28 ), swallowing a single mouthful of contaminated water could cause

illness. Cryptosporidium, and to a lesser extent Giardia, are resistant to disinfection by

chlorine at levels generally used in swimming pools. Although some pools might have

filters and disinfection practices capable of removing or killing parasites, several hours

could be required to completely recirculate and cleanse the pool water. In the meantime,

pool water can become recontaminated. Either way, swimmers remain at risk until all of

the water is recirculated through an effective water treatment process. The risk for

transmission of cryptosporidiosis can increase because of the protracted periods of time

necessary for moving all water through filtration equipment (i.e., turnover rates), problems in the design of pools that result in areas with poor water circulation (dead spots)

(29 ), mixing of water from different pools during filtration, and the depletion of disinfectants by organic matter, which leaves insufficient residual disinfectant (30 ). Because

Cryptosporidium oocysts measure only 4–6 μm in diameter, pool filtration systems that

use sand or other large granular materials (without the special chemical pretreatment

coagulants commonly used by the drinking water industry) might not be effective in

removing oocysts.

The number of reported outbreaks of gastroenteritis in recreational water caused by

bacteria decreased from 10 during 1995–1996 to 4 during 1997–1998. One outbreak was

in a large water park where residual disinfectant would be expected to prevent these

types of outbreaks. Chlorine levels during the period of the outbreak were low when

measured by county public health officials. This underscores the difficulty of maintaining

adequate chlorination levels in large shallow pools used by many young children. Because fecal contaminants and other organic material can rapidly consume the available

chlorine, pool operators need to maintain their disinfectant at regulated levels and test

those levels on a regular and frequent basis.
Vol. 49 / No. SS-4 MMWR 17

In contrast with the outbreaks caused by parasites, most of which were associated

with chlorinated water, 50% (i.e., 2) of the outbreaks attributed to bacteria were associated with unchlorinated water (i.e., lakes) (Figure 4). Freshwater venues, which lack

filtration and disinfection safeguards, present more of a challenge for prevention. Contamination of these venues can require protracted periods of closure or other ways to

limit use, to ensure appropriate water quality. EPA has published criteria for evaluating

the quality of both marine and fresh water used for recreation (16,31 ). Microbial monitoring has been recommended for recreational areas potentially contaminated by sewage or human use. However, epidemiologic studies have not clearly defined what health

risks might be associated with specific levels of total or fecal coliforms detected in bathing waters.

Prevention efforts have focused on providing adequate bathroom facilities (e.g., including diaper-changing areas at recreational areas) and on limiting the number of swimmers per unit area. Other prevention measures can include patron and operator

education, as well as efforts to a) improve filtration methods, disinfection methods, and

pool design and b) change recreational water industry practices (e.g., provide specific

pools with dedicated filtration systems for children so the water is not mixed with adults

pools, limit access of young children to adult pools and operate filtration systems at

higher turnover rates [in keeping with existing state and local regulatory requirements

for suction injuries]). However, such changes can be costly, and the degree to which they

reduce risk is unknown. Development and enforcement of clear and effective policies

regarding fecal accidents in recreational water facilities is needed. However, questions

that still need to be addressed include:

• What is the prevalence of pathogens in formed fecal accidents that are usually

observed by pool operators?

• How long should a pool be vacated after a fecal accident?

• Is it beneficial to drain a pool after a fecal accident?

• Is hyperchlorination a strategy that should be used, especially for

Cryptosporidium?

• What role do swim diapers/pants have in reducing fecal accidents?

Strategies to change behaviors of recreational water guests might also be important.

Public education should stress that swimming is communal bathing and therefore requires good hygiene practices, and that chlorine does not kill all pathogens. Outbreaks of

gastroenteritis associated with recreational water use could be reduced if a) those experiencing diarrhea refrain from swimming and continue to do so for 2 weeks after the

resolution of their diarrhea and b) swimmers avoid swallowing recreational water.

During 1997–1998, most of the reported outbreaks of dermatitis were associated

with hot tubs and pools. The outbreak of Pontiac fever in Wisconsin was also associated

with whirlpool use. Outbreaks of Pseudomonas dermatitis and Pontiac fever associated

with hot tubs are preventable if water is maintained at a pH of 7.2–7.8 with free, residual

chlorine levels in the range of 2.0–5.0 mg/L (32 ). A person’s susceptibility and immersion

time, along with the number of bathers per unit area, also could influence the risk for

infection (33 ). Close operator attention to pool and hot tub bather load, as well as frequent disinfectant level checks and additions could help prevent these outbreaks.
18 MMWR May 26, 2000

During 1997–1998, four deaths were caused by primary amebic meningoencephalitis, which is fewer than the six deaths reported during 1995–1996. Naegleria infections

are generally acquired during the summer months when the temperature of fresh water

is favorable for multiplication of the organism (34,35 ). The ameba could enter a person’s

body through the nasal passages when water is forced up the nose during swimming.

Limiting the amount of fresh water forced into the nasal passages during jumping or

diving (e.g., holding the nose or wearing nose plugs) could reduce the risk for these

infections.

CONCLUSION

Information from the nationwide surveillance for WBDOs is used to characterize the

epidemiology of waterborne diseases in the United States. Data regarding the types of

water systems and deficiencies associated with outbreaks are used to evaluate the

adequacy of current regulations for water treatment and monitoring of water quality.

The identification of the etiologic agents of outbreaks is critical because agents newly

associated with WBDOs could require new methods of control. Trends in the incidence of

WBDOs caused by various etiologic agents can lead to changes in policies or resource

allotment.

For agents that are recognized as important waterborne pathogens, surveillance at

the local and state levels facilitates rapid recognition and control of WBDOs. Close communication among state and local health departments and water utilities is crucial. For

example, if epidemiologic evidence suggests the possibility of waterborne transmission,

water utilities should be contacted promptly and asked about such factors as recent

treatment events and changes in source water quality. Similarly, local policies should be

developed that specify the thresholds for reporting various water-quality data to health

departments. Timely water testing and environmental investigations can help identify an

outbreak’s etiologic agent and the correctable source(s) of water contamination, as well

as establish whether control measures (e.g., boil-water advisories) are indicated.

Ways to improve the WBDO surveillance system should be explored. Reviewing

information gathered through other mechanisms (e.g., issuances of boil-water advisories and computerized data regarding water quality) could help detect WBDOs. Special

epidemiologic studies are needed to supplement the findings of the existing surveillance

system by addressing such issues as the public health importance of newly identified

agents of waterborne disease, the effectiveness of prevention strategies in nonoutbreak

settings, and the timeliness with which state and local health departments act in response to these pathogens.

State health departments can request epidemiologic assistance and laboratory testing from CDC to investigate WBDOs. CDC and EPA can be consulted regarding the engineering and environmental aspects of water treatment and regarding collection of

large-volume water samples to identify pathogenic viruses and parasites, which require

special methods for recovery. Requests for testing for viruses 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 testing for parasites should be made to CDC’s Division of Parasitic Diseases,

NCID, at (770) 488-7760.

Additional information is available from the following sources:
Vol. 49 / No. SS-4 MMWR 19

• EPA’s Safe Drinking Water Hotline, (800) 426-4791 (telephone) or

<sdwa@epamail.epa.gov> (E-mail).

• CDC’s Cryptosporidiosis Information Line of the Parasitic Diseases Information

Line, (888) 232-3228 (voice telephone system) or (888) 232-3299 (fax).

• CDC’s NCID Internet site at <http://www.cdc.gov/ncidod/index.htm>.

Information regarding cryptosporidiosis is available at the Internet site of CDC’s Division of Parasitic Diseases, NCID, which is located at the following address: <http://

www.cdc.gov/ncidod/dpd/parasites/cryptosporidiosis/default.htm>. WBDOs should be

reported to this division by telephone 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; Office of Ground Water and Drinking Water; Hugh McKinnon, and Susan Shaw of the

U.S. Environmental Protection Agency; Robert Tauxe of the Division of Bacterial and Mycotic

Diseases, Roger Glass of the Division of Viral and Rickettsial Diseases, Matthew Arduino of the

Hospital Infections Program, and Dennis Juranek of the Division of Parasitic Diseases, NCID,

CDC; and Mark McClanahan and Lorraine Backer of the Division of Environmental Hazards and

Health Effects, NCEH, CDC.

References

1. Craun GF, ed. Waterborne diseases in the United States. Boca Raton, FL: CRC Press, Inc.,

1986.

2. Levy DA, Bens MS, Craun GF, Calderon RL, Herwaldt BL. Surveillance for waterbornedisease outbreaks—United States, 1995–1996. In: CDC surveillance summaries, December

11, 1998. MMWR 1998;47(No. SS-5):1–33.

3. Kramer MH, Herwaldt BL, Craun GF, Calderon RL, Juranek DD. Surveillance for waterbornedisease outbreaks—United States, 1993–1994. In: CDC surveillance summaries, April 12,

1996. MMWR 1996;45(No. SS-1):1–33.

4. 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.

5. 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.

6. Environmental Protection Agency. 40 CFR Part 141. Water programs: national interim

primary drinking water regulations. Federal Register 1975;40:59566–74.

7. Pontius FW, Roberson JA. The current regulatory agenda: an update. Journal of the

American Water Works Association 1994;86:54–63.

8. Pontius FW. Implementing the 1996 SDWA amendments. Journal of the American Water

Works Association 1997;89:18–36.

9. Environmental Protection Agency. Announcement of the drinking water contaminant

candidate list; notice. Federal Register 1998;63:10274–87.

10. 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.
20 MMWR May 26, 2000

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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. 600/1-84-004.

17. CDC. Outbreak of cryptosporidiosis associated with a water sprinkler fountain—Minnesota,

1997. MMWR 1998;47:856–60.

18. Gilbert L, Blake P. Outbreak of Escherichia coli O157:H7 infections associated with a

water park. Georgia Epidemiology Report 1998;14:1–2.

19. CDC. Outbreak of acute febrile illness among athletes participating in triathlons—Wisconsin

and Illinois, 1998. MMWR 1998;47:585–8.

20. Boyce TG, Pemberton AG, Addiss DG. Cryptosporidium testing practices among clinical

laboratories in the United States. Pediatr Infect Dis J 1996;15:87–8.

21. Craun GF, ed. Methods for the investigation and prevention of waterborne disease

outbreaks. Cincinnati, OH: US Environmental Protection Agency, Health Effects Research

Laboratory, 1990; EPA publication no. 600/1-90/005a.

22. Hoff JC. Inactivation of microbial agents by chemical disinfectants. Cincinnati, OH: US

Environmental Protection Agency, Water Engineering Research Laboratory, Drinking Water

Research Division, 1986; EPA publication no. 600/2-86/067.

23. Robertson JB, Edberg SC. Natural protection of spring and well drinking water against

surface microbial contamination. I. Hydrogeological parameters. Crit Rev Microbiol

1997;23:143–78.

24. Environmental Protection Agency. 40 CFR Parts 141 and 142. Drinking water regulations:

maximum contaminant level goals and national primary drinking water regulations for

lead and copper; final rule. Federal Register 1991;56:26460–4.

25. 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.

26. Seyfried PL, Tobin RS, Brown NE, Ness PF. A prospective study of swimming-related

illness. I. Swimming-associated health risk. Am J Public Health 1985;75:1068–70.

27. DuPont HL, Chappell CL, Sterling CR, Okhuysen PC, Rose JB, Jakubowski W. The infectivity

of Cryptosporidium parvum in healthy volunteers. N Engl J Med 1995;332:855–9.

28. Haas CN, Rose JB. Reconciliation of microbial risk models and outbreak epidemiology:

the case of the Milwaukee outbreak [Abstract]. In: Proceedings of the American Water

Works Association 1994 Annual Conference: Water quality. Denver, CO: American Water

Works Association, 1994:517–23.

29. CDC. Swimming pools: safety and disease control through proper design and operation.

Atlanta, GA: US Department of Health and Human Services, Public Health Service, CDC,

1976; DHHS publication no. (CDC)88-8319.
Vol. 49 / No. SS-4 MMWR 21

30. Carpenter C, Fayer R, Trout J, Beach MJ. Chlorine disinfection of recreational water for

Cryptosporidium parvum. Emerg Infect Dis 1999;5:579–84.

31. Cabelli VJ. Health effects criteria for marine recreational waters. Research Triangle Park,

NC: US Environmental Protection Agency, Office of Research and Development, Health

Effects Research Laboratory, 1983; EPA publication no. 600/1-80-031.

32. CDC. Suggested health and safety guidelines for public spas and hot tubs. Atlanta, GA:

US Department of Health and Human Services, Public Health Service, CDC, 1981; DHHS

publication no. 99-960.

33. Highsmith AK, McNamara AM. Microbiology of recreational and therapeutic whirlpools.

Toxicity Assessment 1988;3:599–611.

34. Visvesvara GS, Stehr-Green JK. Epidemiology of free-living ameba infections. J Protozool

1990;37(suppl):25S–33S.

35. John DT, Howard MJ. Seasonal distribution of pathogenic free-living amebae in Oklahoma

waters. Parasitol Res 1995;81:193–201.
Provided and adequate (Historical information or laborator

chlorinator malfunction or a water detectable free-chlorine residual, ocoliforms in the water]) Not provided or inadequate (e.g., stating that a lake was crowd

Provided and adequate Not provided or inadequate TABLE 1. Classification of investigations of waterborne-disease outbreaks — United States* Class† Epidemiologic data Water-quality data Adequate§ a) Data were provided regarding exposed and unexposed persons; and b) relative risk or odds ratio was 2, or the p-value was <0.05. Adequate Provided, but limited a) Epidemiologic data provided did not meet the criteria for Class I; or b) the claim was made that ill persons had no exposures in common besides water, but no data were provided. Provided, but limited *Outbreaks of Pseudomonas dermatitis and single cases of primary amebic meningoencephalitis or illness resulti

poisoning are not classified according to this scheme. †Based on the epidemiologic and water-quality data provided on CDC form 52.12. §Adequate data were provided to implicate water as the source of the outbreak. IIIIII IV
TABLE 2. Waterborne-disease outbreaks associated with drinking water 

— United States, 1997 (n = 7)*

State Month Class† Etiologic agent No. of Type of Deficiency¶ Source 

cases system§

Colorado Jul III AGI** 9 NCom 3 Spring Florida Mar III Copper poisoning 2 Com 4 Well 

New Mexico Jul I AGI†† 123 NCom 4 Well 

New York Jun I Giardia intestinalis 50 Com 3 Lake 

Oregon Jun III G. intestinalis 100 NCom 4 Well/spring 

South Dakota May I AGI 16 NCom 3 Well 

Washington Sep III Escherichia coli O157:H7 4 NCom 3 Well 

* An outbreak is defined as a) at least two persons experiencing a similar illness after ingestion of drinking water an

evidence that implicates water as the probable source of the illness.

† Based on the epidemiologic and water-quality data provided on CDC form 52.12.§ Com=community; NCom=noncommunity. Community and noncommunity water systems are public water syste

service connections or an average of 

25 residents for 

60 days/year. A community water system serves year-ro

community, subdivision, or mobile home park with 

15 service connections or an average of 

25 residents. A no

system can be nontransient or transient. Nontransient systems serve 

25 of the same persons for >6 months 

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

¶ 1=untreated surface water; 2=untreated groundwater; 3=treatment deficiency (e.g., temporary interruption of disin

inadequate disinfection, and inadequate or no filtration); 4=distribution system deficiency (e.g., cross-connectionwater mains during construction or repair, and contamination of a storage facility); and 5=unknown or miscellaneocontaminated bottled water).

** Acute gastrointestinal illness of unknown etiology.

†† Eleven persons had stool specimens that tested positive for E. coli O86:H11; one stool specimen was also positi
TABLE 3. Waterborne-disease outbreaks associated with drinking water 

— United States, 1998 (n = 10)*

State Month Class† Etiologic agent No. of Type of Deficiency¶ Source 

 cases system§

Florida May III Giardia intestinalis 7 Com 2 Well 

Florida Sep III Copper poisoning 35 Com 3 Well 

Florida Dec III G. intestinalis 2 Ind 2 Well Illinois May III Escherichia coli O157:H7 3 Ind 2 Well 

Minnesota Aug I Shigella sonnei 83 Com 4 Well 

Montana Jul III AGI** 5 Ind 3 Well New Mexico Jul I Cryptosporidium parvum††32 Ind 5 Well Ohio Oct III AGI§§ 10 Com 4 Surface¶¶ 

Texas Jul I C. parvum*** 1400 Com 3 Well 

Wyoming Jun I E. coli O157:H7 157 Com 2 Well/spring 

* An outbreak is defined as a) at least two persons experiencing a similar illness after ingestion of drinking water an

evidence that implicates water as the probable source of the illness.

† Based on the epidemiologic and water-quality data provided on CDC form 52.12.§ Com=community; Ind=Individual. A community water system is a public water system that serves year-round resi

nity, subdivision, or mobile-home park with 

15 service connections or an average of 

25 residents for 

60 days/ye

systems are small systems that are not owned or operated by a water utility and that serve <15 connections or 

¶ 1=untreated surface water; 2=untreated groundwater; 3=treatment deficiency (e.g., temporary interruption of d

cally inadequate disinfection, and inadequate or no filtration); 4=distribution system deficiency (e.g., cross-conntion of water mains during construction or repair, and contamination of a storage facility); and 5=unknown deficiency (e.g., contaminated bottled water).

** Acute gastrointestinal illness of unknown etiology.

†† Nine persons had stool specimens that tested positive only for Cryptosporidium, and one person had a speci

positive for Blastocystis hominis.

§§ One person had a stool specimen that was positive for B. hominis.¶¶ Surface water from an unknown source.

*** Eighty-nine persons had stool specimens that tested positive only for Cryptosporidium, and one person had a sp

positive only for Giardia. None of the specimens were positive for both organisms.
TABLE 4. Waterborne-disease outbreaks associated with drinking water, by etiologic agent and type of water States, 1997

–1998 (n = 17)

Type of water system*

Community Noncommunity Individual 

Etiologic agent Outbreaks Cases Outbreaks Cases Outbreaks Cases Outbreaks AGI† 1 10 3 148 1 5 5 

Copper 2 37 0 0 0 0 2 

Cryptosporidium parvum 1 1,400 0 0 1 32 2 Escherichia coli O157:H7 1 157 1 4 1 3 3 Giardia intestinalis 2 57 1 100 1 2 4 Shigella sonnei 1 83 0 0 0 0 1 

Total (%) 8 1,744 5 252 4 42 17 

(47.1%) (85.6%) (29.4%) (12.4%) (23.5%) (2.1%) (100.0%) 

*Community and noncommunity water systems are public water systems that serve 

15 service connections or 

residents for 

60 days/year. A community water system serves year-round residents of a community, subdivision, or 

with 

15 service connections or an average of 

25 residents. A noncommunity water system can be nontran

Nontransient systems serve 

25 of the same persons for >6 months of the year (e.g., factories or schools), whereas 

do not (e.g., restaurants, highway rest stations, or parks). Individual water systems are small systems not owned or outility that serve <15 connections or <25 persons.

 †Acute gastrointestinal illness of unknown etiology.
TABLE 5. Waterborne-disease outbreaks associated with drinking water, by type of deficiency and type of water States, 1997

–1998 (n = 17)

Type of water system*

Community Noncommunity Individual Tot

Type of deficiency† Outbreaks (%) Outbreaks (%) Outbreaks (%) Outbreaks 

Untreated surface water 0 (0.0) 0 (0.0) 0 (0.0) 0 Untreated groundwater 2 (25.0) 0 (0.0) 2 (50.0) 4 Inadequate treatment 3 (37.5) 3 (60.0) 1 (25.0) 7 Distribution system 3 (37.5) 2 (40.0) 0 (0.0) 5 Miscellaneous or unknown 0 (0.0) 0 (0.0) 1 (25.0) 1 

Total 8 (100.0) 5 (100.0) 4 (100.0) 17 *Community and noncommunity water systems are public water systems that serve 

15 service connections or 

residents for 

60 days/year. A community water system serves year-round residents of a community, subdivision, or 

with 

15 service connections or an average of 

25 residents. A noncommunity water system can be nontran

Nontransient systems serve 

25 of the same persons for >6 months of the year (e.g., factories or schools), whereas 

do not (e.g., restaurants, highway rest stations, or parks). Individual water systems are small systems not owned or o

utility that serve <15 connections or <25 persons.

†1=untreated surface water; 2=untreated groundwater; 3=treatment deficiency (e.g., temporary interruption of disinf

inadequate disinfection, and inadequate or no filtration); 4=distribution system deficiency (e.g., cross-connectionwater mains during construction or repair, and contamination of a storage facility); and 5=unknown or miscellaneocontaminated bottled water).

TABLE 6. Waterborne-disease outbreaks of gastroenteritis associated with recreational water 

— United Stat

State Month Class* Etiologic agent Illness No. of Source 

cases

Massachusetts Jul III Shigella sonnei Gastroenteritis 9 Pool/fountain 

Minnesota Jul II Cryptosporidium parvum Gastroenteritis 369 Fountain 

Missouri Jul I Escherichia coli O157:H7 Gastroenteritis 8 Lake 

*Based on the epidemiologic and water-quality data provided on CDC form 52.12.
TABLE 7. Waterborne-disease outbreaks of gastroenteritis associated with recreational water 

— United Stat

State Month Class* Etiologic agent Illness No. of Source 

cases

Florida Jul IV Cryptosporidium parvum Gastroenteritis 7 Pool 

Georgia Jun I Escherichia coli O157:H7 Gastroenteritis 26 Pool 

Maine Aug I AGI† Gastroenteritis 650 Lake 

Minnesota Apr IV C. parvum Gastroenteritis 45 Pool 

Minnesota Jul IV E. coli O157:H7 Gastroenteritis 5 Lake 

Minnesota Jul IV C. parvum Gastroenteritis 7 Pool 

Ohio Jul III NLV§ Gastroenteritis 30 Lake 

Oregon Aug II C. parvum Gastroenteritis 69 Pool 

Pennsylvania Jul III C. parvum Gastroenteritis 8 Lake 

Washington Jul II AGI Gastroenteritis 41 Lake Washington Jul III AGI Gastroenteritis 248 Lake Wisconsin Jun I NLV Gastroenteritis 18 Lake 

Wisconsin Jun III C. parvum Gastroenteritis 12 Pool Wisconsin Jul III C. parvum Gastroenteritis 9 Pool 

Wisconsin Jul IV C. parvum Gastroenteritis 12 Pool 

*Based on the epidemiologic and water-quality data provided on CDC form 52.12.

†Acute gastrointestinal illness of unknown etiology.§Norwalk-like virus.TABLE 8. Waterborne-disease outbreaks of meningoencephalitis, leptospirosis, and Pontiac fever associated water 

— United States, 1998 (n = 6)

State Month Class* Etiologic agent Illness No. of Source 

cases

Florida Aug NA† Naegleria Meningoencephalitis 1 Stream 

Illinois Jun I Leptospira Leptospirosis 375 Lake Oklahoma Aug NA Naegleria Meningoencephalitis 1 Lake Texas Jul NA Naegleria Meningoencephalitis 1 Lake Texas Aug NA Naegleria Meningoencephalitis 1 River 

Wisconsin Jan I Legionellae Pontiac fever 45 Whirlpool 

*Based on the epidemiologic and water-quality data provided on CDC form 52.12.

† Not applicable.
TABLE 9. Waterborne-disease outbreaks of dermatitis associated with recreational water 

— United States, 1

State Year Month Class* Etiologic agent No. of Source 

cases

Alaska 1998 Jun NA† Pseudomonas aeruginosa§ 50 Spring 

Arkansas 1997 Jan NA P. aeruginosa¶ 12 Pool and hot tIndiana 1997 Feb NA P. aeruginosa§ 42 Pool Maine 1997 Jan NA P. aeruginosa¶ 3 Hot tub 

Maryland 1998 Feb NA P. aeruginosa¶ 7 Hot tub Oregon 1997 Jul IV Schistosoma spindale¶ 2 Lake Wisconsin 1998 Feb NA P. aeruginosa§ 8 Pool 

Wisconsin 1998 Feb NA P. aeruginos¶ 3 Hot tub 

*Based on the epidemiologic and water-quality data provided on CDC form 52.12.

† Not applicable.§ Laboratory-confirmed case.¶ Suspected case based on clinical syndrome.TABLE 10. Waterborne-disease outbreak of gastroenteritis associated with drinking water that was not includesurveillance summary 

— United States, 1996 (n = 1)*

State Month Class† Etiologic agent No. of Type of Deficiency¶ Source 

cases system§

Florida Oct II Norwalk-like virus 594 Com 5 Well *An outbreak is defined as a) at least two persons experiencing a similar illness after ingestion of drinking water an

evidence that implicates water as the probable source of the illness.

 †Based on the epidemiologic and water-quality data provided on CDC form 52.12. §Com=Community. A community water system is a public water system that serves year-round residents of a comm

or mobile-home park with 

15 service connections or an average of 

25 residents for 

60 days/year.

 ¶1=untreated surface water; 2=untreated groundwater; 3=treatment deficiency (e.g., temporary interruption of disinf

inadequate disinfection, and inadequate or no filtration); 4=distribution system deficiency (e.g., cross-connectionwater mains during construction or repair, and contamination of a storage facility); and 5=unknown or miscellaneocontaminated bottled water).
Vol. 49 / No. SS-4 MMWR 29

FIGURE 1. Number of waterborne-disease outbreaks associated with drinking water,

by etiologic agent and month — United States, 1997–1998 (n = 17)

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

agent, water system, water source, and deficiency — United States, 1997–1998 (n = 17)

Etiologic Agent

Unidentified

29.4%

Bacterial

23.5%

Chemical

11.8%

Parasitic

35.3%

Water System

Community

47.1%

Individual

23.5% Noncommunity

29.4%

Water Source

Well

70.6%

Surface

water

11.8% Well and spring

11.8%

Deficiency

Treatment 

deficiency

41.2%

Untreated 

groundwater

23.5%

Distribution 

system

29.4%

Spring

5.9% Miscellaneous

5.9%

0

2

4

6

8

10

12

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

1997 and 1998

Number of outbreaks

Chemical poisoning

Infectious or suspected infectious etiology
30 MMWR May 26, 2000

FIGURE 3. Number of waterborne-disease outbreaks associated with recreational

water, by illness and month — United States, 1997–1998 (n = 32)

FIGURE 4. Waterborne-disease outbreaks of gastroenteritis associated with

recreational water, by etiologic agent and type of exposure — United States, 1997–

1998

*Norwalk-like virus.

†

Acute gastrointestinal illness of unknown etiology.

Etiologic Agent (n = 18)

Cryptosporidium 

parvum

50.0%

Shigella sonnei

5.6% Escherichia coli

O157:H7

16.7%

AGI†

16.7%

Type of Exposure (n = 18)

Fresh water

44.4%

Treated water

55.6%

NLV* 11.1%

Cryptosporidium

parvum

12.5%

Escherichia coli

O157:H7

25.0%

AGI†

37.5%

NLV* 25.0%

Etiologic Agent in Fresh Water (n = 8) Etiologic Agent in Treated Water (n = 10)

Escherichia coli

O157:H7

10.0%

Shigella sonnei

10.0%

Cryptosporidium

parvum

80.0%

0

2

4

6

8

10

12

14

16

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

1997 and 1998

Number of outbreaks

Meningoencephalitis

Dermatitis

Other

Gastroenteritis
Vol. 49 / No. SS-4 MMWR 31

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

by year and etiologic agent — United States, 1971–1998 (n = 691)

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

by year and type of water system — United States, 1971–1998 (n = 691)

*Acute gastrointestinal illness of unknown etiology.

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

0

10

20

30

40

50

60

1971 1974 1977 1980 1983 1986 1989 1992 1995 1998

Year

Individual

Noncommunity

Community

N u m

ber of out

brea

k

s
32 MMWR May 26, 2000

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

water, by year and illness — United States, 1989–1998 (n = 171)

0

5

10

15

20

25

30

35

1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

Year

Other

Dermatitis

Meningoencephalitis

Gastroenteritis

Number of outbreaks
Vol. 49 / No. SS-4 MMWR 33

Glossary

Action level: A specified concentration of a contaminant in water. If this concentration is

reached or exceeded, certain actions (e.g., further treatment and monitoring) must be

taken to comply with a drinking water regulation.

Boil-water advisory: A statement to the public advising persons to boil tap water before

drinking it.

Class: WBDOs are classified according to the strength of the epidemiologic and waterquality data implicating water as the source of the outbreak (Table 1).

Coagulation: 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.

Coliforms: All aerobic and facultative anaerobic, gram-negative, nonsporeforming, rodshaped bacteria that ferment lactose with gas formation within 48 hours at 95 F (35 C).

Community water system: A public water system that serves year-round residents of a

community, subdivision, or mobile home park that has 15 service connections or an

average of 25 residents for 60 days/year.

Contact time: The length of time water is exposed to a disinfectant (e.g., chlorine contact

time).

Cross-connection: Any actual or potential connection between a drinking water supply

and a possible source of contamination or pollution (e.g., a wastewater line).

Cyst: The infectious stage of Giardia intestinalis and some other protozoan parasites that

have protective walls, which facilitate their survival in water and other environments.

Disinfection by-products: Chemicals formed in water through reactions between organic matter and disinfectants.

Distribution system: Water pipes, storage reservoirs, tanks, and other means used to

deliver drinking water to consumers or store it before delivery.

Excystation: The release of the internal (i.e., encysted) contents (e.g., trophozoites or

sporozoites) from cysts or oocysts.

Fecal coliforms: Coliforms that grow and produce gas at 112.1 F (44.5 C) in 24 hours.

Filter backwash: Water containing the material obtained by reversing the flow of water

through a filter to dislodge the particles that have been retained on it.

Filtration: The process of removing suspended particles from water by passing it through

one or more permeable membranes or media of small diameter (e.g., sand, anthracite,

or diatomaceous earth).

Finished water: The water (i.e., drinking water) delivered to the distribution system after

treatment, if any.
34 MMWR May 26, 2000

Flocculation: 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).

Free, residual chlorine level: The concentration of chlorine in water that is not combined

with other constituents, thus serving as an effective disinfectant.

Groundwater system: A system that uses water extracted from the ground (i.e., a well or

spring).

Heterotrophic microflora: Microorganisms that utilize organic material for energy and

growth.

Individual water system: A small water system not owned or operated by a water utility

that serves <15 residences or farms that do not have access to a public water system.

Maximum-contaminant level: The maximum permissible concentration (level) of a contaminant in water supplied to any user of a public water system.

Nephelometric turbidity units: 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.

Noncommunity water system: A public water system that a) serves an institution, industry, camp, park, hotel, or business that is used by the public for 60 days per year, b) has

15 service connections or serves an average of 25 persons, and c) is not a community

water system.

Oocyst: The infectious stage of Cryptosporidium parvum and some other coccidian parasites with a protective wall, which facilitates survival in water and other environments.

Public water system: A system, classified as either a community water system or a

noncommunity water system, that provides piped water to the public for human consumption and is regulated under the Safe Drinking Water Act.

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

Reverse osmosis: A filtration process that removes dissolved salts and metallic ions

from water by forcing it through a semipermeable membrane. This process is also highly

effective in removing microbes from water.

Siphonage: A reversal of the normal flow of water or other liquid caused by a negativepressure gradient (e.g., within a water system).

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

Surface water: The water in lakes, rivers, reservoirs, and oceans.

Total coliforms: Nonfecal and fecal coliforms that are detected with a standard test.

Turbidity: The quality (e.g., of water) of having suspended matter (e.g., clay, silt, or plankton), which results in loss of clarity or transparency.
Vol. 49 / No. SS-4 MMWR 35

Untreated water: Surface water or groundwater that has not been treated in any way

(also called raw water).

Water quality indicator: A microbial, chemical, or physical parameter that indicates the

potential risk for infectious diseases associated with use of 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 given type of hazard or pollution.

Water utility: A water provider that distributes drinking water to a community through a

network of pipes.

Watershed: An area from which water drains to a single point; in a natural basin, the area

contributing flow (i.e., water) to a given place or a given point on a stream.

Watershed-control program: A program to protect a watershed from sources of contamination or pollution.
36 MMWR May 26, 2000
Vol. 49 / No. SS-4 MMWR 1

State and Territorial Epidemiologists and Laboratory Directors

State and Territorial Epidemiologists and Laboratory Directors are acknowledged for their contributions to CDC Surveillance Summaries. The epidemiologists and the laboratory directors listed

below were in the positions shown as of May 2000.

State/Territory Epidemiologist Laboratory Director

Alabama John P. Lofgren, MD William J. Callan, PhD

Alaska John P. Middaugh, MD Bernard Jilly, PhD

Arizona Norman Peterson, MD, MPH Wes Press, MS

Arkansas Thomas C. McChesney, DVM Michael G. Foreman

California Duc J. Vugia, MD, MPH Paul Kimsey, PhD

Colorado Richard E. Hoffman, MD, MPH Ronald L. Cada, DrPH

Connecticut James L. Hadler, MD, MPH Katherine Kelley, DrPH

Delaware A. LeRoy Hathcock, PhD Jane Getchall, DrPH

District of Columbia Martin E. Levy, MD, MPH —

Florida Richard S. Hopkins, MD, MSPH Ming Chan, PhD

Georgia Paul Blake, MD, MPH Elizabeth A. Franko, DrPH

Hawaii Paul V. Effler, MD, MPH Vernon K. Miyamoto, PhD

Idaho Christine G. Hahn, MD Richard H. Hudson, PhD

Illinois Shari L. Bornstein, MD, MPH Bernard T. Johnson, MS

Indiana Robert Teclaw, DVM, PhD, MPH David E. Nauth

Iowa M. Patricia Quinlisk, MD, MPH Mary J. R. Gilchrist, PhD

Kansas Gianfranco Pezzino, MD, MPH Roger H. Carlson, PhD

Kentucky Glyn G. Caldwell, MD Samuel Gregorio, DrPH

Louisiana Louise McFarland, DrPH Henry B. Bradford, Jr, PhD

Maine Kathleen F. Gensheimer, MD, MPH John A. Krueger

Maryland Jeffrey C. Roche, MD, MPH (Acting) J. Mehsen Joseph, PhD

Massachusetts Alfred DeMaria, Jr, MD Ralph J. Timperi, MPH

Michigan Matthew L. Boulton, MD, MPH Frances Pouch Downes, DrPH

Minnesota Richard Danila, PhD, MPH Norman Crouch, PhD

Mississippi Mary Currier, MD, MPH Joe O. Graves, PhD

Missouri H. Denny Donnell, Jr, MD, MPH Eric C. Blank, DrPH

Montana Todd A. Damrow, PhD, MPH Mike Spence, MD

Nebraska Thomas J. Safranek, MD Steve Hinrichs, MD

Nevada Randall L. Todd, DrPH L. Dee Brown, MD, MPH

New Hampshire Jesse Greenblatt, MD, MPH Veronica C. Malmberg, MSN

New Jersey Eddy A. Bresnitz, MD, MS S. I. Shahied, PhD

New Mexico C. Mack Sewell, DrPH, MS David E. Mills, PhD

New York City Benjamin A. Mojica, MD, MPH Alex Ramon, MD, MPH

New York State Perry F. Smith, MD Lawrence S. Sturman, MD, PhD

North Carolina Newton J. MacCormack, MD, MPH Lou F. Turner, DrPH

North Dakota Larry A. Shireley, MPH, MS Bonna Cunningham

Ohio Forrest W. Smith, MD William Becker, DO

Oklahoma J. Michael Crutcher, MD, MPH John Hitz, DrPH

Oregon David W. Fleming, MD Michael R. Skeels, PhD, MPH

Pennsylvania James T. Rankin, Jr, DVM, PhD, MPH Bruce Kleger, DrPH

Rhode Island Utpala Bandyopadhyay, MD, MPH Gregory Hayes, DrPH

South Carolina James J. Gibson, MD, MPH Harold Dowda, PhD

South Dakota Sarah L. Patrick, PhD, MPH Michael Smith

Tennessee William L. Moore, Jr, MD Michael W. Kimberly, DrPH

Texas Dennis M. Perrotta, PhD David L. Maserang, PhD

Utah Craig R. Nichols, MPA Charles D. Brokopp, DrPH

Vermont Peter D. Galbraith, DMD, MPH Burton W. Wilcke, Jr, PhD

Virginia Robert B. Stroube, MD, MPH James L. Pearson, DrPH

Washington Juliet VanEenwyk, PhD (Acting) Jon M. Counts, DrPH

West Virginia Loretta E. Haddy, MS, MA Andrea Labik, PhD

Wisconsin Jeffrey P. Davis, MD Ronald H. Laessig, PhD

Wyoming Karl Musgrave, DVM, MPH Richard Harris, PhD

American Samoa Joseph Tufa, DSM, MPH Joseph Tufa, DSM, MPH

Federated States

of Micronesia Jean-Paul Chaine —

Guam Robert L. Haddock, DVM, MPH Aurelto S. Espinola, MD

Marshall Islands Tom D. Kijiner —

Northern Mariana Islands Jose L. Chong, MD Joseph K.P. Villagomez

Palau Jill McCready, MS, MPH —

Puerto Rico Carmen C. Deseda, MD, MPH José Luis Miranda Arroyo, MD

Virgin Islands Jose Poblete, MD (Acting) Norbert Mantor, PhD
2 MMWR May 26, 2000

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