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Surveillance for Waterborne Disease Outbreaks Associated with Drinking Water --- United States, 2007--2008
Corresponding author: Joan M. Brunkard, PhD, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC, 1600 Clifton Road, N.E., MS C-9, Atlanta, GA 30333. Telephone: 404-639-1700; E-mail: healthywater@cdc.gov.
Abstract
Problem/Condition: Since 1971, CDC, the Environmental Protection Agency (EPA), and the Council of State and Territorial Epidemiologists have collaborated on the Waterborne Disease and Outbreak Surveillance System (WBDOSS) for collecting and reporting data related to occurrences and causes of waterborne disease outbreaks associated with drinking water. This surveillance system is the primary source of data concerning the scope and health effects of waterborne disease outbreaks in the United States.
Reporting Period: Data presented summarize 48 outbreaks that occurred during January 2007--December 2008 and 70 previously unreported outbreaks.
Description of System: WBDOSS includes data on outbreaks associated with drinking water, recreational water, water not intended for drinking (WNID) (excluding recreational water), and water use of unknown intent (WUI). Public health agencies in the states, U.S. territories, localities, and Freely Associated States are primarily responsible for detecting and investigating outbreaks and reporting them voluntarily to CDC by a standard form. Only data on outbreaks associated with drinking water, WNID (excluding recreational water), and WUI are summarized in this report. Outbreaks associated with recreational water are reported separately.
Results: A total of 24 states and Puerto Rico reported 48 outbreaks that occurred during 2007--2008. Of these 48 outbreaks, 36 were associated with drinking water, eight with WNID, and four with WUI. The 36 drinking water--associated outbreaks caused illness among at least 4,128 persons and were linked to three deaths. Etiologic agents were identified in 32 (88.9%) of the 36 drinking water--associated outbreaks; 21 (58.3%) outbreaks were associated with bacteria, five (13.9%) with viruses, three (8.3%) with parasites, one (2.8%) with a chemical, one (2.8%) with both bacteria and viruses, and one (2.8%) with both bacteria and parasites. Four outbreaks (11.1%) had unidentified etiologies. Of the 36 drinking water--associated outbreaks, 22 (61.1%) were outbreaks of acute gastrointestinal illness (AGI), 12 (33.3%) were outbreaks of acute respiratory illness (ARI), one (2.8%) was an outbreak associated with skin irritation, and one (2.8%) was an outbreak of hepatitis. All outbreaks of ARI were caused by Legionella spp.
A total of 37 deficiencies were identified in the 36 outbreaks associated with drinking water. Of the 37 deficiencies, 22 (59.5%) involved contamination at or in the source water, treatment facility, or distribution system; 13 (35.1%) occurred at points not under the jurisdiction of a water utility; and two (5.4%) had unknown/insufficient deficiency information. Among the 21 outbreaks associated with source water, treatment, or distribution system deficiencies, 13 (61.9%) were associated with untreated ground water, six (28.6%) with treatment deficiencies, one (4.8%) with a distribution system deficiency, and one (4.8%) with both a treatment and a distribution system deficiency. No outbreaks were associated with untreated surface water. Of the 21 outbreaks, 16 (76.2%) occurred in public water systems (drinking water systems under the jurisdiction of EPA regulations and water utility management), and five (23.8%) outbreaks occurred in individual systems (all of which were associated with untreated ground water). Among the 13 outbreaks with deficiencies not under the jurisdiction of a water system, 12 (92.3%) were associated with the growth of Legionella spp. in the drinking water system, and one (7.7%) was associated with a plumbing deficiency. In the two outbreaks with unknown deficiencies, one was associated with a public water supply, and the other was associated with commercially bottled water. The 70 previously unreported outbreaks included 69 Legionella outbreaks during 1973--2000 that were not reportable previously to WBDOSS and one previously unreported outbreak from 2002.
Interpretation: More than half of the drinking water--associated outbreaks reported during the 2007--2008 surveillance period were associated with untreated or inadequately treated ground water, indicating that contamination of ground water remains a public health problem. The majority of these outbreaks occurred in public water systems that are subject to EPA's new Ground Water Rule (GWR), which requires the majority of community water systems to complete initial sanitary surveys by 2012. The GWR focuses on identification of deficiencies, protection of wells and springs from contamination, and providing disinfection when necessary to protect against bacterial and viral agents. In addition, several drinking water--associated outbreaks that were related to contaminated ground water appeared to occur in systems that were potentially under the influence of surface water. Future efforts to collect data systematically on contributing factors associated with drinking water outbreaks and deficiencies, including identification of ground water under the direct influence of surface water and the criteria used for their classification, would be useful to better assess risks associated with ground water.
During 2007--2008, Legionella was the most frequently reported etiology among drinking water--associated outbreaks, following the pattern observed since it was first included in WBDOSS in 2001. However, six (50%) of the 12 drinking water--associated Legionella outbreaks were reported from one state, highlighting the substantial variance in outbreak detection and reporting across states and territories. The addition of published and CDC-investigated legionellosis outbreaks to the WBDOSS database clarifies that Legionella is not a new public health issue. During 2009, Legionella was added to EPA's Contaminant Candidate List for the first time.
Public Health Actions: CDC and EPA use WBDOSS surveillance data to identify the types of etiologic agents, deficiencies, water systems, and sources associated with waterborne disease outbreaks and to evaluate the adequacy of current technologies and practices for providing safe drinking water. Surveillance data also are used to establish research priorities, which can lead to improved water quality regulation development. Approximately two thirds of the outbreaks associated with untreated ground water reported during the 2007--2008 surveillance period occurred in public water systems. When fully implemented, the GWR that was promulgated in 2006 is expected to result in decreases in ground water outbreaks, similar to the decreases observed in surface water outbreaks after enactment of the Surface Water Treatment Rule in 1974 and its subsequent amendments. One third of drinking water--associated outbreaks occurred in building premise plumbing systems outside the jurisdiction of water utility management and EPA regulations; Legionella spp. accounted for >90% of these outbreaks, indicating that greater attention is needed to reduce the risk for legionellosis in building plumbing systems. Finally, a large communitywide drinking water outbreak occurred in 2008 in a public water system associated with a distribution system deficiency, underscoring the importance of maintaining and upgrading drinking water distribution system infrastructure to provide safe water and protect public health.
Introduction
Data on waterborne disease outbreaks in the United States have been collected since 1920. Researchers reported these statistics during 1920--36 (1), 1938--1945 (2), 1946--1960 (3), and 1961--1970 (4). Since 1971, CDC, the U.S. Environmental Protection Agency (EPA), and the Council of State and Territorial Epidemiologists (CSTE) have collaborated on the Waterborne Disease and Outbreak Surveillance System (WBDOSS), which tracks the occurrences and causes of outbreaks associated with drinking water and other water exposures. The history of surveillance for waterborne disease outbreaks in the United States has been summarized previously (5). Previously reported data from drinking water--associated outbreaks have been reclassified systematically and analyzed for trends (6). This report presents data on 48 outbreaks that occurred during 2007--2008 and were reported to CDC by public health departments in U.S. states, territories, and localities as well as a previously unreported outbreak that occurred in 2002 and 69 legionellosis outbreaks associated with drinking water, water not intended for drinking (WNID), and water of unknown intent (WUI) that occurred before 2001. Since 2001, legionellosis outbreaks associated with drinking water have been reported to WBDOSS. Legionellosis outbreaks that occurred before 2001 have been added retrospectively to WBDOSS to provide a more complete representation of legionellosis outbreaks associated with drinking water, WNID, and WUI. The data provided in this report represent only a portion of the burden of illness associated with exposure to drinking water. They do not include either endemic waterborne disease cases (sporadic cases not known to be associated with an outbreak) or the estimated number of unrecognized and unreported outbreaks.
Background
Environmental Protection Agency Drinking Water Regulations
The majority of outbreaks described in this report occurred in public drinking water systems (Figure 1). The Safe Drinking Water Act (SDWA) of 1974 and its subsequent 1986 and 1996 amendments authorized EPA to set national standards to protect public drinking water and its sources against naturally occurring or man-made contaminants (7--9). These standards include health-based maximum levels for microbiologic, chemical, and other contaminants in drinking water and water treatment performance criteria for the removal or inactivation of contaminants (Table 1). If needed, EPA can issue guidance or a health advisory instead of a regulation. EPA regulations do not apply to private, individual water supplies. However, certain states and localities might set standards for individual water supplies (e.g., driller licensing and registration, well permitting, and water testing processes). Standards and requirements for private wells vary among states and localities. Commercially bottled water is regulated by the Food and Drug Administration (FDA) (Figure 1).
Additional rules that protect against exposure to waterborne pathogens include the Surface Water Treatment Rule (SWTR) and its amendments (10--15), the Total Coliform Rule (TCR) (16,17), and the 2006 Ground Water Rule (GWR) (18,19). The SWTR and amendments specify water-treatment techniques (e.g., filtration and disinfection), monitoring, and performance criteria for systems that use surface water sources to protect against Giardia and Cryptosporidium contamination. EPA has established criteria to assess whether ground water sources are under the direct influence of surface water, and, if so, these systems are required to meet provisions of the SWTR and amendments. The TCR requires public water systems to monitor for indicators of fecal contamination and take corrective action when they are found. In 2007, EPA established an advisory committee to provide recommendations on revisions to the TCR and on information needed to understand better the public health risks associated with the degradation of water quality in pipes, storage tanks, and other appurtenances used to distribute drinking water to consumers (20). The GWR specifies when corrective action, including disinfection, is required for wells and springs to protect against bacteria and viruses (Table 1). In addition to the rules described above, a program established in the 1986 SDWA amendments, the Wellhead Protection Program, requires states to develop plans to delineate and manage wellhead protection areas and to actively reduce the potential for contamination of all public ground water systems (18).
The SDWA amendments of 1996 require EPA to publish periodically a list of contaminants that must be evaluated for potential regulatory action (21,22) and to establish criteria for a program to monitor unregulated contaminants (23--26). Contaminant Candidate Lists (CCL1, 2 and 3) were published in 1998, 2005, and 2009 (21,22,27). Microbial contaminants are selected for inclusion on the CCL on the basis of three criteria: 1) that the contaminant might have an adverse effect on human health, 2) that the contaminant is known to occur or there is a substantial likelihood that it will occur in public water systems with a frequency and at levels of public health concern, and 3) that regulation of the contaminant presents a meaningful opportunity to reduce health risk (28). In 2009, Legionella pneumophila was added to CCL3 for the first time (22).
Methods
Data Sources
Public health agencies in the states, U.S. territories, localities, and Freely Associated States* (FAS) have primary responsibility for detecting and investigating outbreaks, which they report voluntarily to CDC using a standard form (CDC 52.12, available at http://www.cdc.gov/healthywater/statistics/wbdoss/nors/forms_archive.html). The form solicits data on characteristics of outbreaks (e.g., number of cases, time, and location), results from epidemiologic and environmental investigations, and results from clinical-specimen and water-sample testing. CDC annually requests reports of outbreaks from persons designated as waterborne disease surveillance coordinators and obtains additional information regarding epidemiologic investigations, water quality, and water treatment to supplement submitted outbreak reports as needed. Numeric and text data are abstracted from outbreak report forms and supporting documents and entered into a database for analysis. All of the outbreaks that occurred during 2007--2008 were reported through the paper-based reporting system and analyzed by using SAS 9.2 (SAS Institute, Inc. Cary, North Carolina). To ensure completeness of legionellosis outbreak data for 2007--2008, CDC compared data from WBDOSS with data from the Travel-Associated Legionellosis in the United States System. In addition, data on outbreaks of legionellosis that occurred before 2001 were added to the WBDOSS database.
Definitions
Waterborne Disease Outbreak
Two criteria must be met for an event to be defined as an outbreak associated with drinking water, WNID (excluding recreational water), or WUI: 1) two or more persons must be linked epidemiologically by time, location of exposure to water, and illness characteristics; and 2) the epidemiologic evidence must implicate water as the probable source of illness. Outbreak reports with limited or no environmental data might be included in WBDOSS, but outbreak reports that lack epidemiologic data linking the outbreak to water are excluded.
Reported outbreaks associated with contaminated drinking water, commercially bottled water, ice, beverages made with contaminated water, and water contaminated by malfunctions in equipment or devices in which water is used or distributed (e.g., beverages contaminated by plumbing failures in drink mix/soda machines) are classified as drinking water--associated outbreaks. Outbreaks involving the consumption of beverages containing contaminated ingredients (i.e., other than water) or ice contaminated through human handling are reported to CDC as foodborne disease outbreaks, not waterborne disease outbreaks. WBDOSS report data are categorized on the basis of the location of the water exposure, not the ill person's state of residence. Outbreaks occurring on cruise ships are not reported to WBDOSS; CDC's Vessel Sanitation Program tracks outbreaks of acute gastrointestinal illness (AGI) related to cruise ships (29).
Single Cases
Single cases of illness or injury associated with water exposure are not classified or analyzed as outbreaks but might be reported directly to WBDOSS or through other national surveillance systems. Cases that might be reported directly to WBDOSS include laboratory-confirmed primary amebic meningoencephalitis (PAM) as a result of Naegleria fowleri infection and single cases of chemical or toxin poisoning.
Water Systems
WBDOSS includes data on outbreaks occurring in public and individual water systems. EPA defines a public water system as a system for the provision of water for human consumption through a distribution system that has at least 15 service connections or that regularly serves at least 25 persons (30). An individual system is one that does not meet EPA's definition of a public water system. It typically serves a single family or farm; individual systems are not subject to EPA regulations but might be regulated at the state or local level. Public water systems include community water systems (serving the same persons year round) and noncommunity water systems (which serve the public but generally do not serve the same persons year round). Noncommunity water systems include transient noncommunity systems (serving different persons for >6 months of the year, such as those in parks and restaurants) and nontransient, noncommunity systems (serving the same persons for >6 months out of the year, such as those in schools and factories) (Figure 1). Of the approximately 153,530 public water systems in the United States, 51,651 (33.6%) are community systems, and 101,879 (66.4%) are noncommunity systems, including 83,484 (81.9%) transient systems and 18,395 (18.1%) nontransient systems (Figure 1) (31). Community systems serve 294.3 million persons; of the 51,651 community water systems, 4,156 (8%) are classified by EPA as "large" (serving 10,001--100,000 persons) or "very large" (serving >100,000 persons) and provide water to 77% of the U.S. population. Nontransient, noncommunity systems provide water to 6.2 million persons, and transient noncommunity systems provide water to 13.3 million persons (by definition, these populations also use another type of water system at their residences, except for the limited number of permanent residents of nontransient systems) (31). Although 78% of community water systems are supplied by ground water, more persons (70%) are supplied year-round by community water systems that use surface water (31). Approximately 15% of the U.S. population (15.8 million households) relies on individual water systems that are owned privately (32,33). Private wells that serve <25 persons are not regulated by EPA under SDWA (34).
Water Sources
Drinking water--associated outbreaks are categorized in WBDOSS as having ground water, surface water, or mixed water sources. Ground water sources include springs, aquifers, and wells. Surface water refers to all water found on the surface (e.g., river, lake, or pond) as distinguished from subsurface or ground water. A drinking water system that uses both a ground water and a surface water source is defined by WBDOSS as having a mixed source. Ground water sources that have the potential for surface water contamination and are used to supply drinking water systems may be categorized as ground water under the direct influence of surface water (GWUDI). EPA has specified criteria to identify potential GWUDI, and state and local environmental health agencies conduct site-specific evaluations of water quality, construction characteristics, and geology to determine treatment requirements.
Deficiencies
To understand the circumstances and water system breakdowns that lead to outbreaks, each outbreak is classified as having one or more deficiencies (e.g., in water treatment and operation, water storage and delivery, or premise plumbing) (Table 2). Analyses of outbreak deficiencies provide important information about how the water became contaminated, water system characteristics, and factors leading to waterborne disease outbreaks.
Strength-of-Evidence Classification for Waterborne Disease Outbreaks
All outbreaks reported to WBDOSS for 2007--2008 have been classified according to the strength of 1) epidemiologic and clinical laboratory evidence and 2) environmental evidence implicating water as the vehicle of transmission (Table 3). The classification (i.e., Classes I--IV), which was first used in the 1989--1990 surveillance report (35), is based on the epidemiologic and environmental data reported to WBDOSS.
Outbreaks and subsequent investigations occur under different circumstances, and not all outbreaks can be investigated rigorously. Classifications that do not meet the highest level (I) do not necessarily imply that the investigation was inadequate or incomplete because multiple factors (e.g., timeliness of outbreak detection) contribute to the ability to collect optimal epidemiologic, clinical laboratory, and environmental data.
Additional terms used in this report have been defined elsewhere (Appendix A).
Changes in the 2007--2008 Surveillance Summary
Strength-of-Evidence Classification
Molecular epidemiology is used increasingly to understand pathogen transmission patterns, detect outbreaks, and identify important risk factors and outbreak sources. The criteria used to determine the strength-of-evidence classifications have been revised to reflect the increasing use of molecular characterization of pathogens identified in clinical specimens and environmental samples collected during outbreak investigations. Molecular data that link multiple persons who had an identical water exposure now are considered adequate epidemiologic data to support a Class I or Class II assignment; molecular data that link at least one person to the implicated water exposure now are considered adequate water quality data to support a Class I or Class III assignment. Previously, epidemiologic study data were required to receive a strength-of-evidence classification of I or II. The "epidemiologic data" and "water quality data" categories have been renamed "epidemiologic and clinical laboratory data" and "environmental data," respectively (Table 3).
Number of Cases
Case counts provided in this report were based on the estimated number of total cases if sufficient supporting evidence was provided. For example, this might include applying the attack rate found during a cohort study to the entire population exposed to contaminated water to estimate the total number of ill persons associated with an outbreak. If no "estimated ill" number was provided, the actual number of reported cases (e.g., laboratory-confirmed and probable cases as reported by the state) was used. CDC requests that states report only cases in which primary exposure to water occurs, so secondary cases (e.g., person-to-person transmission among household members) are not included in case counts of waterborne disease in WBDOSS.
Analysis of Deficiencies
Previous WBDOSS surveillance reports limited the descriptive analyses to focus on drinking water--associated outbreaks with source water, treatment, or distribution system deficiencies (i.e., deficiencies 1--4 and 13) (Table 2). However, tables and figures in this report present data for all of the drinking water--associated outbreaks and deficiencies, including those associated with Legionella spp. and building premise plumbing deficiencies (i.e., deficiencies 1--13 and 99).
Legionnaires' Disease Outbreaks Before 2001
Data concerning previously unreported legionellosis outbreaks that occurred before 2001 have been added to the WBDOSS database. These data were abstracted from Epidemic Intelligence Service outbreak investigation reports and peer-reviewed publications. Previously, only Legionnaires' disease (LD) outbreaks that occurred after 2001 were included in WBDOSS.
Results
During 2007--2008, a total of 24 states and Puerto Rico reported 48 outbreaks, including 29 for 2007 and 19 for 2008. Of these, 36 outbreaks were associated with drinking water, eight with WNID, and four with WUI. Outbreaks are tabulated by year and state (Tables 4--6). One outbreak that occurred in 2002 and 69 Legionella outbreaks from 1973--2000 also were included as previously unreported outbreaks (Table 7).
Waterborne Disease Outbreaks Associated with Drinking Water
Since the surveillance system first started in 1971, drinking water--associated outbreaks have been reported every year (Figure 2). The 36 outbreaks described in this report (including 20 in 2007 and 16 in 2008) occurred in 23 states and Puerto Rico (Figure 3). Outbreaks occurred predominantly in the spring through fall, with only three outbreaks reported during November--February. Multiple etiologic agents were implicated in the 36 outbreaks (Table 8). Descriptions of selected outbreaks have been summarized (Appendix B).
The 36 outbreaks reported during 2007--2008 caused illness among at least 4,128 persons and resulted in three deaths. The median number of persons affected in an outbreak was 14 (range: 2--1,663). Four predominant illnesses were reported: 22 (61.1%) outbreak reports of AGI, 12 (33.3%) outbreak reports of acute respiratory illness (ARI), one (2.8%) outbreak report of hepatitis and one (2.8%) outbreak report of skin irritation associated with a chemical exposure. Although the 22 AGI outbreaks were caused by a variety of pathogens, all 12 ARI outbreaks were caused by Legionella (i.e., LD or Pontiac fever [PF]) (Figure 4).
Of the 36 drinking water--associated outbreaks, 17 (47.2%) were assigned a strength-of-evidence rank of Class I, two (5.6%) were ranked as Class II, 14 (38.9%) were ranked as Class III, and three (8.3%) were ranked as Class IV. Drinking water--associated outbreaks were tabulated by etiology, type of water system, and water source (Table 8); deficiency and type of water system (Table 9); and deficiency and water source (Table 10).
Etiology
Of the 36 drinking water--associated outbreaks, 21 (58.3%) were caused by bacteria, five (13.9%) were caused by viruses, three (8.3%) were caused by parasites, and one (2.8%) was caused by a chemical. Two (5.6%) outbreaks had multiple etiologies: one (2.8%) was caused by bacteria and viruses, and one (2.8%) was caused by bacteria and parasites. Four (11.1%) had unidentified etiologies: one was suspected to be caused by norovirus (Table 8; Figure 5).
Bacteria. A total of 21 outbreaks were associated with bacterial agents and resulted in 1,520 cases of illness: 12 outbreaks, 75 cases of illness, and two deaths were caused by Legionella; four outbreaks and 77 cases of illness were caused by Campylobacter; three outbreaks, 1,307 cases of illness, and one death were caused by Salmonella; one outbreak and six cases of illness were caused by E. coli O157:H7; and one outbreak with 55 cases of illness was caused by Providencia spp. (Table 8). An estimated 1,300 cases of illness were related to Salmonella contamination during a single outbreak in Colorado (Table 5; Appendix B).
Viruses. Five outbreaks were associated with viral agents and resulted in 274 cases of illness: four outbreaks with 265 cases of illness were caused by norovirus, and one outbreak with nine cases of illness was caused by hepatitis A.
Parasites. Three outbreaks were associated with parasitic agents and resulted in 163 cases of illness and no reported deaths. Two of these outbreaks with 81 cases of illness were caused by Giardia intestinalis, and one outbreak with 82 cases of illness was caused by Cyclospora cayetanensis.
Chemicals. One outbreak involved a chemical exposure and resulted in an estimated 145 cases of illness following exposure to water containing high levels of sodium hydroxide. No deaths were reported.
Multiple etiologies. Two outbreaks were associated with multiple etiologies and resulted in 270 cases of illness; one outbreak with viral and bacterial agents caused by norovirus genogroup I, Campylobacter, and Salmonella resulted in 229 cases of illness; one outbreak with parasitic and bacterial agents caused by Shigella sonnei, Giardia intestinalis, and Cryptosporidium resulted in 41 cases of illness. No deaths were reported.
Unidentified etiologies. In four outbreaks an etiologic agent was not identified; however, one outbreak had a suspected etiology of norovirus. These four outbreaks resulted in 1,756 cases of AGI; no deaths were reported (Table 8).
Deficiencies
A total of 37 deficiencies were cited in 36 drinking water--associated outbreaks. Of these, 22 (59.5%) involved the source water, treatment facility, or distribution system (eight in community, nine in noncommunity, and five in individual systems), including 13 associated with untreated ground water (deficiency 2), seven associated with treatment deficiencies (deficiency 3), and two associated with distribution system deficiencies (deficiency 4) (Table 9). No outbreaks associated with untreated surface water (deficiency 1) or current treatment processes that are not expected to remove a chemical contaminant (deficiency 13) were reported during this surveillance period (Table 11). Of the 37 deficiencies, 13 (35.1%) occurred in public water systems at points not under the jurisdiction of a water utility, including 12 deficiencies associated with Legionella (deficiency 5A) and one associated with a plumbing system deficiency (deficiency 6); two outbreaks had an unknown deficiency (deficiency 99A, B) (Table 9; Figure 6). No outbreaks reported during 2007--2008 were associated with deficiencies in treatment after the property line or meter; contamination of equipment using or distributing water; contamination during commercial bottling, shipping, hauling, or storage; or contamination at point of use (deficiencies 7--11) (Table 11).
Contamination of Water at/in the Water Source, Treatment Facility, or Distribution System
A total of 21 outbreaks were assigned a deficiency classification of 2--4 (untreated ground water, treatment, and distribution system deficiencies, respectively), including one outbreak that was assigned two deficiency classifications (treatment and distribution system deficiencies). No outbreaks with a deficiency classification of 1 (untreated surface water) or 13 (current treatment processes not expected to remove a chemical contaminant) were reported (Table 11).
Etiology
Nine (42.9%) of these 21 outbreaks were associated with bacteria, five (23.8%) with viruses, three (14.3%) with unidentified etiologies, two (9.5%) with parasites, one with a chemical (4.8%), and one (4.8%) with multiple etiologies (both bacterial and viral agents). Cases in one outbreak with an unidentified etiology had an incubation period, symptoms, and duration of illness that were consistent with norovirus infection.
Water Quality Data
All but one of the 21 outbreaks with a deficiency classification of 2--4 (Tables 2--4) had current water quality data (e.g., laboratory data regarding the presence of coliform bacteria, pathogens, or chemical contaminants) or historic data (e.g., levels of disinfectants) available.
Water Systems
Nine (42.9%) of the 21 outbreaks with deficiencies 2--4 involved noncommunity water systems, five (23.8%) involved individual water systems, and seven (33.3%) involved community water systems (Table 9). Among the nine outbreaks involving noncommunity water systems, six (66.7%) were associated with untreated ground water, and three (33.3%) were associated with a treatment deficiency. All five outbreaks involving individual water systems were associated with untreated ground water. Among the seven outbreaks involving a community water system, eight deficiencies were assigned. Two (28.6%) outbreaks were associated with untreated ground water, three (42.9%) were associated with a treatment deficiency, one (14.3%) was associated with a distribution system deficiency, and one (14.3%) was associated with both a treatment deficiency and a distribution system deficiency (Table 9).
Water Sources
A total of 20 (95.2%) of the 21 outbreaks with deficiencies 2--4 were associated with ground water sources (i.e., wells or springs); one (4.8%) outbreak was associated with surface water derived from a reservoir (Table 10). Among the 20 outbreaks and 21 deficiencies related to ground water sources, 13 (65.0%) outbreaks were associated with consumption of untreated ground water. Well water sources were used by systems in nine of these outbreaks, and springs were water sources in four outbreaks. In one of the outbreaks associated with the use of untreated spring water, the spring was classified by the State as GWUDI and thus subject to EPA regulations for surface water (SWTR and amendments) (10--15). In several other outbreaks, evidence of contamination suggested that the well or spring was under the direct influence of surface water; however, information was not provided on the surveillance form about GWUDI testing and classification.
Six (30.0%) ground water outbreaks were associated with treatment deficiencies, including inadequate disinfection or filtration, interruption of disinfection, and deficiencies in other treatment processes. Two outbreaks in systems using well water were associated with distribution system deficiencies. One large communitywide outbreak was associated with contamination of a distribution system storage tank, and a second outbreak had both distribution system and treatment deficiencies, including cross-connections and inadequate disinfection (Table 10; Appendix B).
Contamination of Water at Points Not Under the Jurisdiction of a Water Utility or at the Point of Use
A total of 13 outbreaks were given a deficiency classification of 5A (Legionella spp. in drinking water systems) or 6 (plumbing system deficiency). Of these 13 outbreaks, 12 (92.3%) were associated with Legionella spp., and one (7.7%) outbreak with multiple etiologies was associated with a plumbing system deficiency (Table 11). No outbreaks reported for 2007--2008 were associated with a deficiency classification of 7--11 (deficiencies in treatment after the property line or meter; contamination of equipment using or distributing water [e.g., drink-mix machines]; and contamination during commercial bottling; shipping, hauling, or storage; and at point of use) (Table 11).
Water Quality Data
Water quality data were available for all 13 outbreaks with a deficiency of 5A or 6. Legionella spp. were isolated from the implicated water source in all of the 12 legionellosis outbreaks.
Legionella in Drinking Water
A total of 12 outbreaks were related to multiplication of Legionella spp. in building plumbing systems. Five (41.7%) of the 12 drinking water--associated legionellosis outbreaks occurred in hospitals, three in nursing homes (25.0%), two in residential buildings (16.7%), one in a hotel (8.3%), and one in an assisted living facility (8.3%). The majority of cases of legionellosis were diagnosed by urinary antigen testing, which is specific for L. pneumophila serogroup 1 (36).
Deficiencies 6--11. One outbreak that had multiple etiologies (both bacterial and parasitic agents were identified) was associated with a plumbing system deficiency (deficiency 6).
Deficiency 99A--B. The deficiency involved in two (5.6%) of the 36 outbreaks could not be identified because the cause of water contamination was unknown. One of the outbreaks occurred in a rural community in Puerto Rico in which persons became ill with Cyclospora cayetanensis. Although an epidemiologic investigation implicated drinking water as the source of exposure in the outbreak, the point at which water was contaminated was not determined, and a deficiency could not be assigned. The second outbreak was associated with commercially bottled water and was assigned a deficiency of 99B. A private residence used a five-gallon water dispenser to supply drinking water. Three persons who replaced an empty container and consumed water from the new container developed gastrointestinal symptoms. Water from the container was not tested, and no etiologic agent was identified. An FDA inspection of the water facility did not find any problems with the bottling process.
Waterborne Disease Outbreaks Associated with Water Not Intended for Drinking (WNID) and Water of Unknown Intent (WUI)
A total of 12 outbreaks were associated with either WNID (n = eight) or WUI (n = four) (Table 6). The 12 WNID/WUI outbreaks caused illness among ≥79 persons, resulting in four deaths, all of which were associated with legionellosis. Of the 12 outbreaks, nine (75.0%) were categorized as ARI and three (25.0%) as AGI. Two (16.7%) of the 12 outbreaks were assigned a strength-of-evidence Class I ranking. No outbreaks were ranked as Class II, four (33.3%) were ranked as Class III, and six (50.0%) were ranked as Class IV.
Etiology
Nine (75.0%) of the 12 WNID/WUI outbreaks were attributed to L. pneumophila serogroup 1, with one of these outbreaks also being attributed to L. pneumophila serogroup 7; the nine legionellosis outbreaks affected 46 persons and resulted in four deaths. One (8.3%) of the WNID/WUI outbreaks was attributed to G. intestinalis. Of the two outbreaks that did not have an identified etiology, one outbreak was suspected to be caused by norovirus (Table 6).
Deficiencies
Each of the 12 WNID/WUI outbreaks was assigned one deficiency: six (50.0%) WNID outbreaks involved Legionella spp. in the water system (deficiency 5B), three (25.0%) WUI outbreaks involved Legionella spp. (deficiency 5C), two (16.7%) WNID outbreaks of AGI involved unidentified etiologies (deficiency 12), and one (8.3%) WUI outbreak involved contamination of an unknown water source (deficiency 99D) (Tables 2 and 6).
Previously Unreported Outbreaks
A total of 70 previously unreported outbreaks that occurred from 1973--2002 were added to WBDOSS during 2010. One previously unreported WNID (deficiency 12) outbreak of Mycobacterium mageritense occurred in 2002 (Table 7). Two patients were diagnosed with M. mageritense infections on their feet following separate visits to a nail salon. Environmental samples from the nail salon isolated M. mageritense in foot bath, drain, and hand sink samples. M. goodii and M. smegma also were isolated in foot bath samples (37).
A total of 69 legionellosis outbreaks that occurred during 1973--2000 were added to the surveillance system in 2010 (Table 7). These data were abstracted from Epidemic Intelligence Service outbreak investigation reports and peer-reviewed publications (38--75). Seventeen outbreaks were associated with drinking water, 26 with WNID, and 26 with WUI (Figure 7). Among these 69 outbreaks, 1,520 cases and 237 deaths were reported from 27 states.
Surveillance Reports Not Classified as Waterborne Disease Outbreaks
Two outbreak reports about occupational exposures did not meet the criteria for inclusion in the surveillance system because either water did not appear to be the source of exposure or evidence was insufficient. In one event, five persons were injured at a water treatment plant; chlorine gas was released following an accidental mixing of sodium hypochlorite and hydrofluorosilicic acid. The second event involved two housecleaners who poured ammonia into a toilet suspected to have contained water with high concentrations of chlorine. One person later called a local poison control center (PCC) to report eye pain and respiratory irritation; however, insufficient epidemiologic and water quality data were available to warrant inclusion of this report as a waterborne disease outbreak. Six additional single case reports that were associated with known or suspected chemical exposures occurring primarily at the point of water use also were excluded because single cases do not meet the case definition for an outbreak. These single cases were identified by one state that conducted an independent review of supplemental data sources for occupational diseases and chemical poisonings, including PCC inquiries and reports submitted to the Hazardous Substances Emergency Events Surveillance (HSEES) system. Although single cases are not classified as outbreaks, the case reports highlight the potential to detect waterborne illness and injury at a state level through collaboration with other existing surveillance systems.
Discussion
The outbreaks reported during this surveillance period highlight several important public health challenges associated with drinking water in the United States. The large proportion of outbreaks associated with untreated or inadequately treated ground water in particular indicate that additional efforts are needed to monitor and protect ground water sources from contamination and to ensure that adequate, continuous treatment is provided when it is needed. Legionella continues to be the most frequently reported etiology among drinking water--associated outbreaks and was also the predominant etiology among WNID and WUI outbreaks. However, more than half of the legionellosis outbreaks reported during 2007--2008 were from one state, demonstrating the substantial variance in outbreak detection, investigation and reporting across states. All deaths except one reported during this surveillance period were associated with Legionella, underscoring the need for improved methods of elimination and control of Legionella, particularly in settings with vulnerable populations. In addition, a large communitywide outbreak associated with contamination of a storage tank underscores the importance of protecting and maintaining drinking water distribution system infrastructure. This report also includes the addition of data concerning 69 legionellosis outbreaks, providing a more complete representation of legionellosis outbreaks in the United States before 2001.
Outbreaks Associated with Drinking Water
Illness and Etiology
During 2007--2008, AGI was the dominant illness type (associated with 61% of drinking water--associated outbreaks) in contrast with the prior surveillance period (2005--2006) in which half of drinking water--associated outbreaks were associated with ARI (78). Of the 36 outbreaks, 24 (67%) were caused by bacteria, five (14%) by viruses, three (8%) by parasites, one (3%) by a chemical, and two (6%) by multiple etiologies. Four (11%) outbreaks had unidentified etiologies.
Bacteria
Since its addition to WBDOSS in 2001, Legionella has been the single most commonly reported pathogen identified in drinking water--associated outbreaks. During 2007--2008, a total of 12 (33.3%) of the 36 reported drinking water--associated outbreaks involved Legionella spp.; half of these outbreaks were reported by one state (New York). Unlike other waterborne bacterial outbreaks that also might be foodborne, zoonotic, or spread person-to-person, legionellosis outbreaks are almost exclusively associated with exposure to colonized water; therefore, Legionella spp. might be more likely than other waterborne pathogens to be associated successfully with a water source during outbreak investigations. All legionellosis outbreaks reported herein occurred as a result of colonization of premise plumbing and pipes (i.e., infrastructure that neither is under the jurisdiction of a water utility nor is regulated by EPA). EPA has no contaminant level specific to Legionella spp. but believes that if parasites and viruses are removed or inactivated according to the treatment techniques in the SWTR and amendments, Legionella will be controlled at the water source (10). However, this does not ensure control within the water distribution system. Because Legionella is the predominant drinking water--related pathogen in WBDOSS, increased attention is needed to understand its ecology, the characteristics contributing to its pathogenicity, the need for improved diagnostics (e.g., molecular tests) and national laboratory testing capacity, and the interventions that are most effective to prevent ongoing disease transmission (6,76--78). EPA's recent inclusion of Legionella in CCL3 might lead to additional research that improves risk-reduction interventions.
During the 2007--2008 surveillance period, nine drinking water--associated outbreaks involved only bacteria (excluding Legionella spp.) compared with two during 2005--2006, five during 2003--2004, and three during 2001--2002. The nine bacterial outbreaks involved chlorine-sensitive pathogens (e.g., Campylobacter, Salmonella, Providencia, and E. coli), including five outbreaks associated with ground water sources in public water systems, highlighting the importance of protecting ground water sources and providing adequate treatment and filtration where needed. The ongoing occurrence of bacterial outbreaks, despite available and efficacious treatment practices, underscores the need for source water protection and adequate disinfection when needed for ground water systems (79) in community, noncommunity, and individual water systems. A large outbreak of Salmonella Typhimurium occurred in a community water system using untreated ground water. The outbreak was associated with contamination in a storage reservoir and emphasizes the importance of protecting water quality in the distribution system, particularly in systems that use untreated ground water sources or have other system vulnerabilities.
The outbreak of Providencia is the first documented drinking water outbreak of this bacterium known to be reported in the United States. An epidemiologic investigation indicated that 55 persons developed gastroenteritis associated with drinking water from a community water system served by a well. Six of nine stool samples from ill persons tested positive for Providencia and negative for other bacteria (Campylobacter, Shigella, and E. coli), norovirus, and parasites. Previously thought to be nonpathogenic (80), Providencia was identified as the cause of a large foodborne outbreak in Japan in 1996 (81) and is thought to be a potential source of travelers' diarrhea (82). Whether Providencia is a true human pathogen or an indicator of exposure to fecally contaminated water or food remains unclear (83).
Viruses
Five outbreaks involving only viruses were reported during 2007--2008, four involving norovirus and one involving hepatitis A virus. All five outbreaks involved contaminated ground water that was either untreated or treated improperly (inadequate or interrupted chlorination as the only treatment provided). These types of events are anticipated to decrease as the GWR is fully implemented. However, one of these viral outbreaks occurred in an individual water system, and the GWR does not apply to private systems.
Parasites
Parasites were identified in three outbreaks reported during 2007--2008. An outbreak linked epidemiologically to a drinking water system in Puerto Rico was caused by C. cayetanensis (84), a rarely reported source of drinking water outbreaks in developed countries. This is the first known reported outbreak of cyclosporiasis associated with drinking water in the United States or associated territories since 1990. A previous outbreak of cyclosporiasis that occurred in Chicago in 1990 was suspected to be associated with water exposure (85). In the 2008 outbreak, residents reported recent interruptions in the community water supply and changes in water quality. A pumping station was determined to be damaged, and a water tanker had been used to haul treated water from a neighboring system to fill a water tank during the same time period. In addition to the C. cayetanensis outbreak, two outbreaks of giardiasis occurred in public water systems using ground water; one outbreak was associated with the improper installation of a filter (86) and the other with a well that was possibly GWUDI (87).
Chemicals
Only one outbreak during 2007--2008 involved a chemical exposure. The outbreak occurred within a public water system after a sodium hydroxide overfeed occurred at the water-treatment facility, raising the pH level of the drinking water supply and injuring an estimated 145 persons. Although a mechanism was in place to monitor pH levels at the treatment plant, the system was not designed to provide automatic notification of offsite staff regarding the problem. The response effort required collaboration among local and state agencies to flush the contaminated water from the distribution system, provide guidance to the community, and make safe drinking water available to local residents. This event highlights the need for appropriate remote monitoring systems in water treatment facilities when staff members are not onsite and the value for public water systems of developing comprehensive incident response plans with involvement from state and local agencies.
Multiple Etiologies and Unidentified Etiologies
Two outbreaks involving multiple etiologies occurred during 2007--2008; one outbreak was caused by norovirus genogroup I, Campylobacter spp. and Salmonella spp., and the other was caused by S. sonnei, G. intestinalis, and Cryptosporidium. The occurrence of multiple etiologic agent outbreaks emphasizes the importance of considering more than one etiology in outbreak investigations, collecting appropriate clinical and environmental specimens, and requesting appropriate diagnostic testing for each agent type. One outbreak was associated with sewage contamination of a well, underscoring the importance of proper waste management and water system protection, and the other outbreak was associated with a plumbing system and cross-connection deficiency. A dinner cruise boat connected to a municipal water supply from a dock had a cross-connection that might have allowed backsiphonage of lake water contaminated with sewage into the boat's potable water supply (88). The outbreak occurred after a period of heavy rainfall and flooding that resulted in the release of a large volume of storm water containing highly diluted sewage into the lake in which the boats were located.
The etiologies of four outbreaks could not be identified, although norovirus was suspected in one outbreak on the basis of symptoms, incubation period, and duration of illness. These four outbreaks represent 11.1% of the 36 drinking water--associated outbreaks reported during 2007--2008, which is among the lowest proportion of outbreaks caused by an unidentified etiology since the beginning of the surveillance system in 1971. This continues a decreasing trend in the proportion of outbreaks caused by an unidentified etiology (6).
The identification of etiologic agents depends on the ability of investigators to recognize the outbreak in a timely manner and for appropriate clinical and environmental samples to be collected and analyzed for the organism, chemical, or toxin of interest. WBDOSS data suggest that these capabilities are improving. During 1971--1996, the etiologic agent was unidentified in 48% (312/645) of drinking water--associated outbreaks whereas during 1997--2008, the etiologic agent was unidentified in 23% (40/174) of outbreaks. This decrease likely reflects improved diagnostic capabilities of laboratories and improvements in outbreak investigations, resulting in more rapid and appropriate specimen collection. Reasons for improved etiologic attribution might also include increased testing and testing capabilities for viral agents in clinical specimens and water samples and improved water sampling and testing methods.
Deficiencies
Outbreaks associated with untreated or inadequately treated source water and distribution system contamination are assigned deficiencies 1--4 and 13. EPA regulations associated with the Safe Drinking Water Act are applicable to public water systems from the water source up to the water meter, the property line, or entry into the building or house, and these deficiencies are important in assessing regulatory strategies. Although individual water systems are not regulated by EPA, the same problems might affect these systems including contamination of pipes or storage infrastructure.
During 2007--2008, 58.3% of all drinking water--related outbreaks (n = 21) and 59.5% of deficiencies (n = 22) involved deficiencies 2--4. One outbreak was associated with more than one deficiency (deficiencies 3 and 4). Deficiencies 1 and 13 were not implicated in any outbreak during the 2007--2008 surveillance period. No outbreaks in public water systems have been associated with the use of untreated surface water since 1990.
Untreated Ground Water
Of the 36 drinking water--associated outbreaks reported during 2007--2008, a total of 13 (36.1%) were associated with contaminated ground water, indicating that contamination of ground water remains a public health problem. Eight (61.5%) of these 13 outbreaks occurred in public water systems, including six in noncommunity water systems and two in community water systems. Factors potentially contributing to these outbreaks included improperly constructed or sited wells, improperly maintained or placed septic systems, contamination by wild or domestic animals, periods of heavy rainfall, and contamination of wells through limestone or fissured rock. Included in the outbreaks associated with improper well construction was a large outbreak of giardiasis in which 35 persons in New Hampshire reported becoming ill after their community drinking water system's well became contaminated with G. intestinalis. The well was approximately 40 feet from a brook that had evidence of beaver habitation and was likely under the influence of surface water (87). New Hampshire Department of Environmental Services regulations require that wells be placed ≥50 feet from sources of surface water (89), but the well owner had not sought a permit before construction. Following an investigation, the well was disconnected from the water system.
In another outbreak, five persons who drank from a noncommunity water system using untreated, contaminated spring water became ill with salmonellosis (Salmonella serotype I 4,5,12:i:-) (90). Although this serotype has been identified in foodborne disease outbreaks reported to CDC, this is the first report to WBDOSS of an outbreak with this serotype. Several factors potentially contributed to the outbreak, including the poor protection of the spring from contamination (including by runoff and wildlife) and lack of disinfection. Pulsed-field gel electrophoresis patterns for a patient's stool and tap water collected from the patient's residence and another distribution system sample were identical. In addition, investigators noted that the geology of the area (porous limestone [karst]) might have increased the likelihood that the spring was under the influence of surface water (90). The spring water tested positive for E. coli (it was not tested for Salmonella), which suggested that the spring was the source of the contamination.
Outbreaks can occur even when wells and septic systems are built according to existing codes. An extensive investigation of a multiple pathogen (norovirus, Campylobacter, and Salmonella) outbreak that sickened 229 persons in Wisconsin revealed that these pathogens were likely introduced into a noncommunity water system through fissures in the underlying dolomite rock that made the system particularly vulnerable to interconnections between the septic system and the well. The investigators noted that the septic system and well were built in accordance with state codes, so it is unlikely that the source of the outbreak would have been identified had the investigators not conducted a rigorous multifaceted investigation (including epidemiologic, laboratory, and hydrologic examinations). As a result of the outbreak, the well water now is being treated with a combination of UV and chlorination (91).
Eight of thirteen outbreaks associated with contaminated ground water during 2007--2008 occurred in noncommunity or community water systems that are subject to EPA's GWR. In 2006, the GWR was promulgated for all public systems that use ground water as a source of drinking water. The GWR establishes a risk-based approach to target ground water systems that are vulnerable to fecal contamination and comprises four major components: 1) sanitary surveys, 2) source water monitoring to test for the presence of indicators of fecal contamination in the ground water source, 3) corrective action, and 4) compliance monitoring to ensure that the treatment technology installed to treat drinking water reliably achieves ≥99.99% (4 log) inactivation and/or removal of viruses (92). States are required to perform initial sanitary surveys on the majority of community water systems by 2012; the remainder of the community water systems (the best performing systems) and all noncommunity drinking water systems must be surveyed by the end of 2014 (92). Operators of ground water systems that are identified as being at risk for fecal contamination must take corrective action to reduce the potential for illness from exposure to microbial pathogens.
The remaining five outbreaks associated with untreated ground water deficiencies occurred in individual water systems. Potential contributing factors in these outbreaks included septic system problems, contamination of wells by domestic or wild animals, flooding and heavy rain, and cracks in the well casing. These systems are not subject to the GWR. Approximately 15 million households in the United States have private wells (33). To safeguard the quality of well water, homeowners should seek information on protective measures and implement recommended operation and maintenance guidelines for private well usage. Recommendations for protecting private wells have been published previously (93--95).
Ground Water Under the Direct Influence of Surface Water
In several outbreaks associated with the use of untreated ground water or treatment deficiencies, the water source appeared to be GWUDI (e.g., microscopic particulate analysis testing identified algae and diatoms, the well was located <50 feet from a surface water source, or the spring was not protected from surface runoff). If a drinking water source is determined to be GWUDI, it is subject to SWTR requirements and amendments and may be classified as a surface water source by the state. Systems using GWUDI must disinfect their water and either provide filtration or meet criteria for avoiding filtration. EPA has developed a consensus method for assessing whether ground water is under the direct influence of surface water (98). However, WBDOSS currently does not collect information on whether ground water systems are under the influence of surface water, nor do states have standard case definitions and criteria for categorizing a system as GWUDI. Establishing a more standardized system for capturing data on GWUDI will be particularly important in better understanding the potential contributing factors and risks between ground water systems and those that have unique challenges associated with surface water influence.
Treatment Deficiencies
Seven outbreaks (19.4%) were associated with treatment deficiencies (deficiency 3) during 2007--2008. Six (85.7%) of these treatment deficiencies were associated with failures to treat contaminated ground water adequately. Multiple treatment-related factors potentially contributed to these outbreaks, including temporary interruption of disinfection, chronically inadequate disinfection, lack of disinfection, and inadequate filtration. When these deficiencies are considered with deficiency 2, contaminated ground water was determined to be the single largest contributing factor in outbreaks associated with drinking water in 2007--2008, underscoring the need for source water protection and adequate disinfection of ground water sources.
Two outbreaks were reported in public systems that provided filtration and disinfection, but both systems experienced treatment failures preceding the outbreak. One outbreak was reported in a noncommunity system using contaminated spring water and was responsible for 46 cases of giardiasis (86). This spring was classified as GWUDI and therefore subject to EPA's SWTR and amendments. Although the system had installed a slow sand filter and chlorinator, inadequate time was allowed for formation of a schmutzdecke† biologic layer on the surface of the filter, which is important for effective treatment performance of slow sand filters. When a slow sand filter is first constructed, the bed of clean sand cannot, strictly speaking, be called a filter because the vital living organisms on which effective filtration depends are not yet present. Building up the biologic content of a new filter is a slow but necessary process. Until the filter is sufficiently "ripened," the filter should not be put into service. Water samples collected 1 week after the filter was put into operation indicated considerably higher levels of total coliforms and turbidity in filtered water samples than in the spring water samples. On the basis of these samples, this system did not meet the treatment requirements of the TCR and SWTR and amendments (97). However, 6 weeks after operation of the filter, a schmutzdecke layer formed, and water samples met requirements.
The second outbreak was reported in a community water system that used surface water from a reservoir. The water was treated conventionally with coagulation, settling, filtration, and disinfection; however, operator error and the interruption of chlorination for 1--2 hours allowed partially disinfected water to enter the distribution system directly through a bypass pipe. During this time, the system did not meet the treatment requirements for disinfection as defined by the SWTR and amendments. The system was recycling filter backwash water as required by EPA (98); however, before the outbreak, the backwash water erroneously bypassed the recovery basin and ozonation before filtration, thereby adversely affecting filter performance. This investigation combined monitoring data with modeling of the distribution system to identify potential system vulnerabilities and sources of contamination. In conjunction with a boil water order notice, the health department asked that residents in the affected area report symptoms of gastrointestinal illness. A cross-sectional, randomly selected household survey was conducted in the affected area to assess potential associations between tap water consumption and gastrointestinal illness. The study identified increased risk for gastrointestinal illness among households that consumed tap water during the period before the boil water notice and also identified substantial dose-response effects and statistically significant trends, with higher rates of illness associated with increased tap water consumption. An extensive list of short- and long-term recommendations was provided through an independent investigation to address system deficiencies and operational issues at the treatment plant.
Distribution System Deficiencies
During 2007--2008, two drinking water--related outbreaks involving distribution system deficiencies occurred, including a large communitywide outbreak of salmonellosis that required local, regional, state, and federal emergency response. An estimated 1,300 persons became ill; 122 infections were laboratory-confirmed, and one person died. The likely source of the outbreak was animal contamination of a storage tank that had numerous cracks and entry points (99). The post outbreak inspection of the water system also identified >100 possible cross-connections in the distribution system, although these were not thought to contribute directly to the outbreak (99). This was one of the largest outbreaks in a community water system in recent years and highlights the critical importance of robust inspection of storage facilities, identification of potential cross-connections during required sanitary surveys, and the staffing and resources for adequate follow-up to ensure that deficiencies have been addressed. The other outbreak associated with a distribution system deficiency was related to a cross-connection between a well serving a residential community and a noncommunity water system. Additional deficiencies and contributing factors included inadequate disinfection and filtration along with a sewage lift that was out of service; this was the only outbreak reported during this surveillance period with two deficiencies noted.
Cross-connections and backsiphonage represented the largest underlying contributing factors among distribution system deficiencies identified in drinking water outbreaks reported during 1971--2006 (6), indicating that greater attention should be focused on cross-connection and backflow prevention and on maintaining the integrity of the distribution system. Drinking water quality within the distribution systems of public water supplies is assessed by monitoring requirements under EPA's Total Coliform Rule. The 2010 revisions to the TCR include a focus on research and information collection needs in the distribution system to protect public health (100). Seven high-priority areas needing additional focus (cross-connections, storage, water main breaks and pressure transients, intrusion, nitrification, contaminant accumulation, and biofilms) were identified by a steering committee selected by EPA and the Water Research Foundation as part of the Research and Information Collection Partnership (101).
Legionella
Legionellosis includes two clinically distinct syndromes: LD, characterized by severe pneumonia, and PF, a febrile illness that includes cough and does not progress to pneumonia. Legionellosis outbreaks accounted for 33.3% of all drinking water--associated outbreaks reported during 2007--2008 and 91.7% of all deficiencies occurring outside the jurisdiction of regulations or water utility management, indicating that legionellosis is a serious public health issue. Approximately 8,000--18,000 cases of LD occur each year in the United States (102), and incidence appears to be increasing (103). Cases typically manifest as LD rather than PF, but regardless of the syndrome, the source of legionellosis outbreaks typically share common features (e.g., warm stagnant water, inadequate biocide concentrations, and aerosolization, which provides the mechanism for inhalation).
The outbreaks of legionellosis reported during this surveillance period highlight the challenges related to its detection and prevention. Surveillance for legionellosis is passive, and the approach to surveillance, outbreak response, and reporting varies substantively by state. For example, six of 12 LD outbreaks associated with drinking water during this surveillance period were reported from one state, emphasizing the variance in outbreak detection, investigation, and reporting across states. However, there appear to be true differences in disease incidence across the United States, with the highest rates of disease reported in the northeast (103). LD is underdiagnosed because the majority of patients with community-acquired pneumonia are treated empirically with broad-spectrum antibiotics (104). However, because Legionella spp. are not transmitted from person-to-person and are always acquired from an environmental source, even a single case of LD implies the presence of a contaminated water source to which others can be exposed. Certain host factors (e.g., underlying lung disease and immunodeficiencies) influence the development and severity of legionellosis. As a result of underdiagnosis and underreporting, identification of two or more cases of LD in association with a potential source is adequate justification for conducting an investigation.
During 2007--2008, nine (75.0%) of 12 legionellosis outbreaks associated with drinking water occurred in health-care or long-term--care settings, demonstrating the propensity for Legionella spp. to colonize potable water systems and underscoring the importance of maintaining a high index of suspicion for legionellosis in health-care settings and in other settings with vulnerable populations. Although Legionella spp. can live in a free state, they often colonize biofilms and free-living protozoa frequently found inside large, complex hospital plumbing systems (79,105). This protects Legionella from biocides and temperature extremes and allows the bacteria to amplify to levels sufficient to be transmitted and cause disease. Persons in hospitals or elderly living facilities are at increased risk as a result of advanced age and a high prevalence of underlying chronic medical conditions.
An outbreak of legionellosis in a health-care setting should prompt both epidemiologic and environmental investigations. Additional cases might point to water exposures that contributed to the outbreak. Environmental sampling of the potable water system and devices that aerosolize water (e.g., cooling towers) can confirm the source of the outbreak and lead to targeted interventions that prevent additional cases. Each health-care facility should develop a plan for legionellosis prevention to address conditions that support Legionella growth in the potable water supply. Guidelines for reducing the risk for legionellosis associated with building water systems are available (106).
Waterborne Disease Outbreaks Associated with Water Not Intended for Drinking and Water of Unknown Intent
During 2007--2008, a total of 12 outbreaks occurred that were associated with WNID or WUI. Nine (75.0%) of these outbreaks were associated with Legionella spp., three (33.3%) with cooling towers, one (11.1%) with an ornamental fountain, and one (11.1%) with recycled water from a vehicle washing station. Four (44.4%) legionellosis outbreaks had an unidentified source of exposure. Of the nine legionellosis outbreaks associated with WNID/WUI, two occurred in long-term--care or assisted living facilities, two occurred at hospitals, and one occurred at an apartment complex for seniors. As noted previously, it is important to address Legionella colonization in and near buildings that house high-risk populations. Although potable water systems within buildings are implicated frequently in health-care--associated outbreaks, other sources of aerosolized water on site and in the surrounding community (e.g., cooling towers and decorative fountains) also should be considered. Aerosols containing Legionella can travel great distances; an investigation of an outbreak among residents of a long-term--care facility implicated a cooling tower that was 0.4 km from the facility (107).
Previously Unreported Outbreaks
This report incorporates 69 outbreaks of legionellosis from 27 states during 1973--2000 that were added to the surveillance system in 2010 and one previously unreported outbreak of M. mageritense from 2002. Legionellosis outbreaks associated with drinking water, WNID, and WUI were not included in WBDOSS before 2001. During 2009--2010, CDC conducted a comprehensive search of the peer-reviewed scientific literature and CDC outbreak investigation reports to capture the historic record of legionellosis outbreaks since the disease was first recognized in 1976; additional legionellosis outbreaks occurring before 1976 were identified later. Legionellosis outbreaks that occurred after 1971 were included in the analysis to correspond with the period when the surveillance system was started (Table 7). The legionellosis outbreaks identified (covering 1971--2000) are likely an underestimate of legionellosis outbreaks that occurred during this period, and caution should be used when interpreting the reported data (Figures 2 and 7). For example, because reporting mechanisms have changed over time (e.g., only published outbreaks and Epi-Aids are included before 2001, whereas all outbreaks reported by state health departments are included as of 2001), comparisons over time cannot be made, and these data might not be representative of the number of outbreaks over time. However, the addition of the pre-2001 outbreaks to WBDOSS underscores the point that legionellosis outbreaks have occurred consistently over the past 3 decades.
Limitations
WBDOSS and waterborne disease outbreak reporting is subject to at least four main limitations. First, the level of surveillance and reporting activity varies across states and localities. Therefore, determining whether an increase or decrease in reporting reflects an actual change in the incidence of outbreaks or reflects a change in the sensitivity of surveillance practices is unknown. Outbreak reporting might increase as waterborne disease becomes better recognized, water system deficiencies are identified, and state surveillance activities and laboratory capabilities increase (108--110). Environmental testing and laboratory capacity also vary substantially across states and localities.
Second, detection, investigation, and reporting of outbreaks are incomplete. Multiple factors contribute to the ability of state and local public health agencies to recognize, investigate, and report outbreaks. Public health agencies must have the financial and personnel resources to investigate outbreaks; they must recognize and link cases of illness to a common water source, which requires appropriate epidemiologic, environmental, and laboratory capacity to conduct investigations. For example, analyses for specific pathogens and indicators of water contamination depend upon the availability of certified or approved laboratories. Although many laboratories are certified to conduct standard analyses for fecal indicators and chemicals, few laboratories have capabilities for identifying waterborne pathogens, and these tests can be expensive. Collecting water samples for pathogen identification often requires sampling large quantities of water or filtering large volumes of water through special membranes. Methods for concentrating large volumes of water for testing are being developed and implemented for use in outbreak investigations (89,111--113).
Third, outbreaks associated with drinking water are inherently difficult to detect because most persons have daily exposure to tap water. For this reason, case-control and other epidemiologic studies are less likely to find statistically significant associations unless the outbreaks are communitywide or environmental investigations provide supporting data to identify deficiencies in water treatment or distribution systems that can help identify drinking water as the potential exposure.
Finally, gaps exist in the types of data that are systematically collected and reported during outbreak investigations. In particular, data from environmental investigations on contributing factors associated with outbreaks (e.g., distribution system vulnerabilities, classification of GWUDI systems including testing criteria, or details on septic system placement and maintenance) are often not collected or reported to CDC. Water samples also often are not collected or are collected late in an investigation, limiting the ability to link clinical and environmental data to establish a water-related exposure through molecular epidemiologic or other laboratory testing. Success in the detection of a pathogen in water samples is highly dependent on a timely investigation and sample collection before contamination is flushed from the water system or inactivated by a disinfectant.
Conclusion
Data collected as part of the national WBDOSS are used to describe the epidemiology of waterborne disease outbreaks in the United States. Trends regarding water systems and deficiencies implicated in these outbreaks are used to assess whether regulations for water treatment and water quality monitoring are adequate to protect public health. Trends regarding the etiologic agents responsible for these outbreaks are used to assess the need for different interventions and changes in policies and resource allocations.
The data provided in this report highlight two primary findings. The first is the high proportion of outbreaks associated with contaminated ground water, whether consumed untreated or with inadequate treatment. This is consistent with data from 1971--2006 indicating that ground water outbreaks comprised the majority of drinking water outbreaks and showed no decrease over time (6). The second finding is that Legionella was again the most frequently reported etiology among drinking water--associated outbreaks, following the pattern observed since it was first included in WBDOSS in 2001 (6). The addition of published and CDC-investigated legionellosis outbreaks to the database demonstrates that legionellosis is not a new public health issue.
Federal drinking water regulations have focused on protecting consumers from contaminated surface water, in part because of previous outbreaks and analyses that suggested needed improvements for surface water systems and the large percentage of the population served by surface water (70% of those using community water systems) (31). These regulations have likely contributed to the decrease in the number and proportion of reported outbreaks associated with contaminated surface water during the previous twenty years. Similar protections for ground water were absent until promulgation of the GWR in 2006. The GWR focuses on identification of deficiencies, protection of wells and springs from contamination, and providing disinfection where necessary to protect against bacterial and viral agents. Outbreaks in disinfected ground water systems emphasize the importance of maintaining adequate, continuous disinfection. Outbreaks in untreated ground water systems underscore the importance of assessing contamination sources to determine if the ground water source is at risk of contamination from fecal sources or is under the direct influence of surface water where additional treatment is needed to protect against parasites. When fully implemented, the GWR is expected to reduce ground water-associated outbreaks, as seen in surface water outbreaks after promulgation of the SWTR and its amendments.
Surveillance, prevention, and control activities for outbreaks occur primarily at the local and state levels (including territories and FAS). CDC and other federal agencies provide technical assistance with laboratory testing and epidemiologic and environmental investigations when requested by states and territories (Box 1). Efforts to improve the detection, investigation, and reporting of outbreaks at the local, state, and national levels include the 2006 CSTE position statement that made waterborne disease outbreaks, as a unit of reporting, nationally notifiable and reportable to CDC starting in 2007. To improve timeliness and completeness of outbreak reporting, in 2009, CDC transitioned to electronic outbreak reporting through the National Outbreak Reporting System (NORS) for outbreaks occurring on or after January 1, 2009 (114,115). NORS is a collaborative project that is currently used for national surveillance of waterborne disease outbreaks, foodborne disease outbreaks, and enteric disease outbreaks associated with zoonotic, person-to-person, environmental, and undetermined exposures. Efforts to develop and enhance NORS functionality focus on the need to support public health agencies and researchers working to identify the causes of outbreaks and to understand the environmental factors contributing to these outbreaks.
Adequate programmatic funding and human resources to investigate outbreaks are essential for an effective surveillance system. Improved communication among local and state public health departments, regulatory agencies, and water utilities, along with routine reporting or sharing of water quality data within the health and environmental departments will aid in the detection and control of outbreaks. Additional data are needed to better understand some of the contributing factors associated with many drinking water outbreaks (e.g., a GWUDI classification with details on criteria used to determine the influence of surface water). Further research and exploration of other contributing factors and antecedent events associated with untreated ground water outbreaks are needed, including systematic documentation and reporting of the role of septic system contamination, extreme precipitation events, improper well construction, main breaks, cross-connections, and treatment failures.
Measures to reduce the occurence of drinking water outbreaks in the United States have been outlined (Box 2).
Additional efforts are needed to improve outbreak detection and investigations. Such efforts include enhancing surveillance activities, increasing laboratory support for clinical specimen and water sample testing, conducting environmental investigations to assess outbreak deficiencies and contributing factors, and providing adequate resources and staff to state and local health departments to monitor, detect, and prevent outbreaks.
Acknowledgments
This report is based in part by contributions from state, local, and territorial waterborne disease surveillance coordinators; state, local and territorial epidemiologists; and environmental health personnel.
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* Includes the Republic of the Marshall Islands, the Federated States of Micronesia, and the Republic of Palau; formerly part of the U.S.-administered Trust Territory of the Pacific Islands.
† Gelatinous biologic layer on the surface of a slow sand filter, consisting of a complex microbial community (including bacteria, fungi, protozoa, and rotifera and other aquatic organisms) and organic particulate matter.
Abbreviations: EPA = Environmental Protection Agency; FDA = Food and Drug Administration.
* In certain instances, bottled water is used in lieu of a community supply or by noncommunity systems.
Alternative Text: The figure shows the types of drinking water systems in the United States, including public water systems (community and noncommunity) and individual (privately owned) water systems.
|
TABLE 7. (Continued) Previously unreported outbreaks (n = 70) associated with drinking water, water not intended for drinking, and water of unknown intent, by state --- Waterborne Disease and Outbreak Surveillance System, United States, 1973--2002* |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
|
State |
Month |
Year |
Class† |
Etiology |
Predominant illness§ |
No. of cases[deaths] (n = 1,522 [237¶]) |
Deficiency** |
Setting |
|
|
California |
Nov |
1997 |
II |
L. pneumophila serogroup 1 |
ARI |
8 |
[1] |
5C |
Community/Municipality |
|
Missouri |
Jul |
1997 |
III |
L. pneumophila serogroup 1, L. bozemanii |
ARI |
4 |
--- |
5B |
Hospital/Health-care facility |
|
Pennsylvania |
May |
1998 |
IV |
L. pneumophila serogroup 1 |
ARI |
7 |
--- |
5B |
Community/Municipality |
|
Georgia |
Sep |
2002 |
III |
Mycobacterium mageritense |
Skin |
2 |
--- |
12 |
Nail salon |
|
Abbreviations: ARI = acute respiratory illness; Skin = illnesses, conditions, or symptoms related to skin. * Previously unreported legionellosis outbreaks included in this table were identified through a review of the published literature on Legionella as well as reports from past CDC-led investigations occurring during 1971--2000. Data are presented on the basis of a review and interpretation of available outbreak investigation reports and published articles. † On the basis of epidemiologic, clinical laboratory, and environmental data (e.g., water quality data) provided to CDC. § The category of illness reported by ≥50% of ill respondents. ¶ Deaths are included in the overall case count. ** Deficiency classification for drinking water, water not intended for drinking (excluding recreational water), and water of unknown intent (see Table 2). †† No deaths were reported. §§ Some or all cases might have been Pontiac fever. |
|||||||||
FIGURE 2. Number of waterborne disease outbreaks associated with drinking water (n = 818),* by year and etiology --- Waterborne Disease and Outbreak Surveillance System, United States, 1971--2008
* Some outbreaks from prior reporting periods were added, reclassified, or excluded during an extensive review (Craun GF, Brunkard JM, Yoder JS, et al. Causes of outbreaks associated with drinking water in the United States from 1971 to 2006. Clin Microbiol Rev 2010;23:507--28); therefore, data are not comparable to figures in previous reports.
† Legionnaires' disease (LD) was reported to the Waterborne Disease and Outbreak Surveillance System (WBDOSS) beginning in 2001. A review of publications and CDC-led investigations during 1971--2000 resulted in the addition of 17 historic LD drinking water outbreaks to WBDOSS.
§ Includes all bacteria except Legionella.
Alternative Text: The figure shows the number of waterborne disease outbreaks associated with drinking water that were reported in the United States during 1971-2008, by year and etiology. A total of 818 outbreaks were reported during 1971-2008.
FIGURE 3. Number of waterborne disease outbreaks associated with drinking water (n = 36), by state/jurisdiction --- Waterborne Disease and Outbreak Surveillance System, United States, 2007--2008*
* These numbers are largely dependent on reporting and surveillance activities in individual states/jurisdictions, and do not necessarily indicate the true incidence of waterborne disease outbreaks.
Alternative Text: The figure shows a map of the United States indicating for each state and Puerto Rico the number of waterborne disease outbreaks associated with drinking water that were reported during 2007-2008. A total of 36 outbreaks were reported. These numbers are largely dependent on reporting and surveillance activities in individual states, and do not necessarily indicate the true incidence of waterborne disease outbreaks in a given state.
FIGURE 4. Percentage of waterborne disease outbreaks asscociated with drinking water, by predominant illness and etiology --- Waterborne Disease and Outbreak Surveillance System, United States, 2007--2008
Abbreviations: AGI = acute gastrointestinal illness; ARI = acute respiratory illness; Hep = viral hepatitis; Skin = illnesses, conditions, or symptoms related to skin.
* All hepatitis infections were attributed to hepatitis A virus.
† One outbreak was associated with exposure to water that contained elevated levels of sodium hydroxide.
§ One outbreak involved bacterial and viral agents. A second outbreak involved bacterial and parasitic agents.
¶ All acute respiratory illness was attributed to Legionella spp.
** Three outbreaks. Norovirus was suspected in one outbreak on the basis of incubation period, symptoms, and duration of illness.
Alternative Text: The figure shows the percentage of drinking water-associated outbreaks that were reported in the United States during 2007-2008, by predominant illness and etiology. Acute gastrointestinal illness was associated with 61.1% of the 36 outbreaks; acute respiratory illness with 33.3%; viral hepatitis with 2.8%; and illnesses, conditions, or symptoms affecting the skin with 2.8%.
FIGURE 5. Percentage of waterborne disease outbreaks associated with drinking water, by etiology, water system, and water source --- Waterborne Disease and Outbreak Surveillance System, United States, 2007--2008*
* Not limited to deficiencies 1--4, and therefore figure is not comparable to those in previous summaries.
† Percentages do not add up to 100% due to rounding.
§ One outbreak involved bacterial and viral agents. A second involved bacterial and parasitic agents.
¶ Other than Legionella spp.
Alternative Text: The figure shows the percentage of waterborne disease outbreaks associated with drinking water that were reported in the United States during 2007-2008, by etiologic agent, water system, and water source. Of 36 outbreaks, 55.6% occurred in community water systems, 27.8% in noncommunity systems, 13.9% in individual water systems, and 2.8% in bottled water. Water sources were ground water for 61.1% of outbreaks, surface water for 36.1%, and mixed water for 2.8%.
FIGURE 6. Percentage of waterborne disease outbreaks associated with drinking water, by deficiency* and water system† --- Waterborne Disease and Outbreak Surveillance System, United States, 2007--2008
* There were 36 waterborne disease outbreaks but 37 deficiencies. See Table 2 for a list of all deficiencies.
† For deficiencies 2, 3, and 5A only. See Table 9 for a summary of all 37 outbreak deficiencies by water system.
§ Percentages do not add up to 100.0% due to rounding.
¶ Deficiencies 99A and 99B.
Alternative Text: The figure shows the percentages of deficiencies linked to drinking water-associated outbreaks. Of the 37 reported deficiencies, untreated ground water was associated with 35.1%, Legionella in drinking water system with 32.4%, treatment deficiency with 18.9%, distribution system with 5.4% plumbing system with 2.7%, and unknown with 5.4%.
FIGURE 7. Number of waterborne disease outbreaks associated with drinking water, water not intended for drinking (WNID) (excluding recreational water), and water use of unknown intent (WUI), by year and etiology --- Waterborne Disease and Outbreak Surveillance System, United States, 1971--2008
* Since 2001, legionellosis outbreaks associated with drinking water, WNID, and WUI have been reported to WBDOSS by public health jurisdictions, and Legionella is presented as its own bacterial etiologic category. Outbreaks that occurred before 2001 were identified through a literature review of journal publications and CDC-led investigation reports.
† Includes all bacteria except Legionella.
Alternative Text: The figure shows the number of waterborne-disease outbreaks associated with drinking water, water not intended for drinking (excluding recreational water), and water use of unknown intent, that occurred in the United States during 1971-2008, by year and etiology. A total of 867 outbreaks were reported before the addition of pre-2001 legionellosis outbreaks compared with 936 after the addition of these outbreaks.
|
BOX 1. Federal organizations that provide assistance with investigations of waterborne disease outbreaks |
|---|
|
State and territorial health departments can request epidemiologic assistance, water quality assessment, and laboratory testing from CDC during waterborne disease outbreaks. Collection of large-volume water samples might be required to identify pathogens that require special protocols for their recovery. The EPA Safe Drinking Water Hotline can be consulted for information about drinking water rules, guidance, and regulations or to identify state and local laboratories certified for drinking water quality testing. The U.S. Geological Survey can be consulted for assistance with hydrogeologic investigations of outbreaks when untreated ground water is suspected. Requests for assistance with outbreak investigations (e.g., epidemiologic assistance, water testing, diagnosis of free-living amebas, or molecular characterization of Cryptosporidium and Giardia) Waterborne Disease Prevention Branch Division of Foodborne, Waterborne, and Environmental Diseases National Center for Emerging and Zoonotic Infectious Diseases, CDC Telephone: 404-639-1700 Email: healthywater@cdc.gov Internet: http://www.cdc.gov/healthywater Requests for diagnostic testing for viral organisms Division of Viral Diseases National Center for Immunization and Respiratory Diseases, CDC Telephone: 800-232-4636 Requests for diagnostic testing for enteric bacterial organisms Enteric Diseases Laboratory Branch Division of Foodborne, Waterborne, and Environmental Diseases National Center for Emerging and Zoonotic Infectious Diseases, CDC Telephone: 404-639-3334 Requests for information for diagnostic testing for parasites (except for Cryptosporidium, Giardia, or free-living amebas) Division of Parasitic Diseases and Malaria Center for Global Health, CDC Telephone: 404-718-4745 Internet: http://www.cdc.gov/parasites Requests for information or testing for Legionella Division of Bacterial Diseases National Center for Immunization and Respiratory Diseases, CDC Telephone: 404-639-2215 Internet: http://www.cdc.gov/legionella Information regarding drinking water and public health CDC Internet: http://www.cdc.gov/healthywater/drinking --- Drinking water health communication and education resources for the general public --- Information on maintaining individual wells and effectively disinfecting water when camping, hiking, or traveling --- Outbreak investigation toolkit and technical information concerning laboratory diagnostics Safe Drinking Water Hotline Environmental Protection Agency Telephone: 800-426-4791 E-mail: hotline-sdwa@epa.gov Internet: http://www.epa.gov/safewater Microbiological and chemical exposure assessment Environmental Protection Agency Microbiological and Chemical Exposure Assessment Research Division National Exposure Research Laboratory Telephone: 513-569-7303 Information about groundwater resources U.S. Geological Survey Internet: http://water.usgs.gov/ogw |
Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of
Health and Human Services.
References to non-CDC sites on the Internet are
provided as a service to MMWR readers and do not constitute or imply
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