A summary of key findings:
CDC MMWR
https://www.cdc.gov/mmwr/volumes/66/wr/mm6644a3.htm?s_cid=mm6644a3_e
Surveillance for Waterborne Disease Outbreaks Associated with Drinking Water — United States, 2013–2014
Weekly / November 10, 2017 / 66(44);1216–1221
Summary
What is already known about this topic?
Waterborne disease and outbreaks associated with drinking water continue to occur in the United States. CDC collects data on waterborne disease outbreaks submitted from all states and territories through the National Outbreak Reporting System.
What is added by this report?
During 2013–2014, a total of 42 drinking water–associated outbreaks were reported to CDC, resulting in at least 1,006 cases of illness, 124 hospitalizations, and 13 deaths. Legionella was responsible for 57% of outbreaks and 13% of illnesses, and chemicals/toxins and parasites together accounted for 29% of outbreaks and 79% of illnesses. Eight outbreaks caused by parasites resulted in 289 (29%) cases, among which 279 (97%) were caused by Cryptosporidium and 10 (3%) were caused by Giardia duodenalis. Chemicals or toxins were implicated in four outbreaks involving 499 cases, with 13 hospitalizations, including the first outbreaks associated with algal toxins.
What are the implications for public health practice?
Continued public health surveillance is necessary to detect waterborne disease and monitor health trends associated with drinking water exposure. When drinking water is contaminated by infectious pathogens, chemicals, or toxins, public health agencies need to provide rapid detection, identification of the cause, and response to prevent and control waterborne illness and outbreaks. Effective water management programs in buildings at increased risk for Legionella growth and transmission can reduce the risk for disease from drinking water pathogens.
Provision of safe water in the United States is vital to protecting public health (1). Public health agencies in the U.S. states and territories* report information on waterborne disease outbreaks to CDC through the National Outbreak Reporting System (NORS) (https://www.cdc.gov/healthywater/surveillance/index.html). During 2013–2014, 42 drinking water–associated† outbreaks were reported, accounting for at least 1,006 cases of illness, 124 hospitalizations, and 13 deaths. Legionella was associated with 57% of these outbreaks and all of the deaths. Sixty-nine percent of the reported illnesses occurred in four outbreaks in which the etiology was determined to be either a chemical or toxin or the parasite Cryptosporidium. Drinking water contamination events can cause disruptions in water service, large impacts on public health, and persistent community concern about drinking water quality. Effective water treatment and regulations can protect public drinking water supplies in the United States, and rapid detection, identification of the cause, and response to illness reports can reduce the transmission of infectious pathogens and harmful chemicals and toxins.
To provide information about drinking water–associated waterborne disease outbreaks in the United States in which the first illness occurred in 2013 or 2014 (https://www.cdc.gov/healthywater/surveillance/drinking-surveillance-reports.html), CDC analyzed outbreaks reported to the CDC Waterborne Disease and Outbreak Surveillance System through NORS (https://www.cdc.gov/nors/about.html) as of December 31, 2015. For an event to be defined as a waterborne disease outbreak, two or more cases must be linked epidemiologically by time, location of water exposure, and illness characteristics; and the epidemiologic evidence must implicate water exposure as the probable source of illness. Data requested for each outbreak include 1) the number of cases, hospitalizations, and deaths; 2) the etiologic agent (confirmed or suspected); 3) the implicated water system; 4) the setting of exposure; and 5) relevant epidemiologic and environmental data needed to understand the outbreak occurrences and for determining the deficiency classification.§ One previously unreported outbreak with onset date of first illness in 2012 is presented but is not included in the analysis of outbreaks that occurred during 2013–2014.
Public health officials from 19 states reported 42 outbreaks associated with drinking water during the surveillance period (Table 1) (https://www.cdc.gov/healthywater/surveillance/drinking-water-tables-figures.html). These outbreaks resulted in at least 1,006 cases of illness, 124 hospitalizations (12% of cases), and 13 deaths. At least one etiologic agent was identified in 41 (98%) outbreaks. Counts of etiologic agents in this report include both confirmed and suspected etiologies, which differs from previous surveillance reports. Legionella was implicated in 24 (57%) outbreaks, 130 (13%) cases, 109 (88%) hospitalizations, and all 13 deaths (Table 1). Eight outbreaks caused by two parasites resulted in 289 (29%) cases, among which 279 (97%) were caused by Cryptosporidium, and 10 (3%) were caused by Giardia duodenalis. Chemicals or toxins were implicated in four outbreaks involving 499 cases, with 13 hospitalizations, including the first reported outbreaks (two outbreaks) associated with algal toxins in drinking water.
The most commonly reported outbreak etiology was Legionella (57%), making acute respiratory illness the most common predominant illness type reported in outbreaks (Table 2). Thirty-five (83%) outbreaks were associated with public (i.e., regulated), community or noncommunity water systems,¶ and three (7%) were associated with unregulated, individual systems. Fourteen outbreaks occurred in drinking water systems with groundwater sources and an additional 14 occurred in drinking water systems with surface water sources. The most commonly cited deficiency, which led to 24** (57%) of the 42 drinking water–associated outbreaks, was the presence of Legionella in drinking water systems. In addition, 143 (14%) cases were associated with seven (17%) outbreak reports that had a deficiency classification indicating “unknown or insufficient information.”
Among 1,006 cases attributed to drinking water–associated outbreaks, 50% of the reported cases were associated with chemical or toxin exposure, 29% were caused by parasitic infection (either Cryptosporidium or Giardia), and 13% were caused by Legionella infection (Table 2). Seventy-five percent of cases were linked to community water systems. Outbreaks in water systems supplied solely by surface water accounted for most cases (79%). Of the 1,006 cases, 86% originated from outbreaks in which the predominant illness was acute gastrointestinal illness. Three (7%) outbreaks in which treatment was not expected to remove the contaminant were associated with a chemical or toxin and resulted in 48% of all outbreak-associated cases.
Discussion
Water treatment processes, regulations, and rapid response to illness outbreaks continue to reduce the transmission of pathogens, reduce exposure to chemicals and toxins, and protect the public drinking water supplies in the United States. Outbreaks reported during this surveillance period include the first reports of drinking water–associated outbreaks caused by harmful algal blooms as well as the continued challenges of preventing and controlling illnesses and outbreaks caused by Legionella and Cryptosporidium. Outbreaks in community water systems caused by chemical spills (West Virginia) (2), harmful algal blooms (Ohio), Cryptosporidium (Oregon) (3), and Legionella (Michigan) demonstrated that diverse contaminants can cause interruptions in water service, illnesses, and persistent community concern about drinking water quality. Outbreaks in community water systems can trigger large and complex public health responses because of their potential for causing communitywide illness and decreasing the availability of safe water for community members, businesses, and critical services (e.g., hospitals). These outbreaks highlight the importance of public health and water utility preparedness for emergencies related to contamination from pathogens, chemicals, and toxins.
Legionella continues to be the most frequently reported etiology among drinking water–associated outbreaks (4). All of the outbreak-associated deaths reported during this surveillance period as well as all of the outbreaks reported in hospital/health care settings or long-term care facilities, were caused by Legionella. A review of 27 Legionnaires’ disease outbreak investigations in which CDC participated during 2000–2014 identified at least one water system maintenance deficiency in all 23 investigations for which this information was available, indicating that effective water management programs in buildings at increased risk for Legionella growth and transmission (e.g., those with more than 10 stories or that house susceptible populations) can reduce the risk for Legionnaires’ disease (5,6). Although Legionella was detected in drinking water, multiple routes of transmission beyond ingestion of contaminated water more likely contributed to these outbreaks, such as aerosolization from domestic or environmental sources. Cryptosporidium was the second most common cause of both outbreaks and illnesses, demonstrating the continued threat from this chlorine-tolerant pathogen when drinking water supplies are contaminated. Existing drinking water regulations and filtration systems targeted to control Cryptosporidium help protect public health in community water systems that are primarily served by surface water sources or groundwater sources under the influence of surface water (7). Through the Epidemiology and Laboratory Capacity for Infectious Diseases (ELC) Cooperative Agreement, CDC has recently begun a laboratory-based cryptosporidiosis surveillance system in the United States, CryptoNet, to better track Cryptosporidium transmission and rapidly identify outbreak sources through molecular typing (8). The cyanobacterial toxin microcystin caused the largest reported toxin contamination of community drinking water in August 2013 and September 2014 and was responsible for extensive community and water disruptions. In June 2015, the Environmental Protection Agency released specific health advisory guidance for microcystin concentrations in drinking water (9). The contamination of a community drinking water supply with 4-metholcyclohexanementanol (MCHM) also illustrates the importance of source water protection from chemicals and toxins (2).
The findings in this report are subject to at least three limitations. First, 17% of drinking water–associated outbreak reports could not be assigned a specific deficiency classification other than “unknown or insufficient information,” because of a lack of information. Furthermore, the deficiency classification most frequently reported (“presence of Legionella in drinking water systems”) does not provide insight into the specific factors contributing to Legionella amplification and transmission. Second, the detection and investigation of outbreaks might be incomplete. Because of universal exposure to water, linking illness to drinking water is inherently difficult through traditional outbreak investigation methods (e.g., case-control and cohort studies) (10). Finally, reporting capabilities and requirements vary among states and localities. Therefore, outbreak surveillance data likely underestimate actual occurrence of outbreaks and should not be used to estimate the actual number of outbreaks or cases of waterborne disease.
Public health surveillance is necessary to detect waterborne disease and outbreaks, and to continue to monitor health trends associated with drinking water exposure. Despite resource constraints, 19 states reported drinking water–associated outbreaks for 2013–2014 compared with 14 for the previous reporting period (4). In this reporting cycle, more reported outbreaks and cases were caused by parasites and chemicals than by non-Legionella bacteria, and more cases were reported from community systems than from individual systems. Most of the outbreaks and illnesses reported in this period were in community systems, which serve larger numbers of persons; outbreaks in these systems can sicken entire communities. Although individual, private water systems likely serve fewer persons than community systems, they can still result in relatively large numbers of illnesses. One outbreak reported during 2013–2014 in an individual system led to 100 estimated illnesses associated with a wedding. The public health challenges highlighted here underscore the need for rapid detection, identification of the cause, and response when drinking water is contaminated by infectious pathogens, chemicals, or toxins to prevent and control waterborne illness and outbreaks.
Acknowledgments
State, territory, and local waterborne disease coordinators, epidemiologists, and environmental health personnel; Bryanna Cikesh, Allison Miller, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC; Jessica Smith, Sooji Lee, Albert Barskey, Chris Edens, Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, CDC
MMWR
https://www.cdc.gov/mmwr/volumes/65/wr/mm6522e1.htm
Vital Signs: Deficiencies in Environmental Control Identified in Outbreaks of Legionnaires’ Disease — North America, 2000–2014
Weekly / June 10, 2016 / 65(22);576 - 584
Laurel E. Garrison, MPH1; Jasen M. Kunz, MPH2; Laura A. Cooley, MD1; Matthew R. Moore, MD1; Claressa Lucas, PhD1; Stephanie Schrag, DPhil1; John Sarisky, MPH2; Cynthia G. Whitney, MD1 (View author affiliations)
View suggested citation
Key Points
• Legionnaires’ disease is a lung infection that is fatal for about one in 10 persons who become infected. Legionella, the bacterium that causes Legionnaires’ disease, grows well in warm water, but can be killed by disinfectants, such as chlorine. Persons can get Legionnaires’ disease when they breathe in small droplets of water contaminated with Legionella.
• Persons most likely to get Legionnaires’ disease are those aged ≥50 years, smokers, and persons with underlying medical conditions, such as chronic lung disease or weakened immune systems.
• Legionella grows best in building water systems that are not well maintained, especially where levels of chlorine or other disinfectants are low and water temperatures are optimal for its growth. Legionnaires’ disease outbreaks most often occur in hotels, long-term care facilities, and hospitals. The most common sources are potable water (e.g., drinkable water used for showering), cooling towers, hot tubs, and decorative fountains.
• The key to preventing outbreaks is good management of building water systems, according to new industry standards. Outbreaks have occurred because of process failures (65%), human errors (52%), equipment failures (35%), external conditions (35%), or a combination of these (48%). Building owners and managers should determine if their building water systems are at increased risk for Legionella growth and spread. If so, they should develop and use a Legionella water management program according to the new industry standards (http://www.cdc.gov/legionella/WMPtoolkit).
• Additional information is available at http://www.cdc.gov/vitalsigns.
Abstract
Background: The number of reported cases of Legionnaires’ disease, a severe pneumonia caused by the bacterium Legionella, is increasing in the United States. During 2000–2014, the rate of reported legionellosis cases increased from 0.42 to 1.62 per 100,000 persons; 4% of reported cases were outbreak-associated. Legionella is transmitted through aerosolization of contaminated water. A new industry standard for prevention of Legionella growth and transmission in water systems in buildings was published in 2015. CDC investigated outbreaks of Legionnaires’ disease to identify gaps in building water system maintenance and guide prevention efforts.
Methods: Information from summaries of CDC Legionnaires’ disease outbreak investigations during 2000–2014 was systematically abstracted, and water system maintenance deficiencies from land-based investigations were categorized as process failures, human errors, equipment failures, or unmanaged external changes.
Results: During 2000–2014, CDC participated in 38 field investigations of Legionnaires’ disease. Among 27 land-based outbreaks, the median number of cases was 10 (range = 3–82) and median outbreak case fatality rate was 7% (range = 0%–80%). Sufficient information to evaluate maintenance deficiencies was available for 23 (85%) investigations. Of these, all had at least one deficiency; 11 (48%) had deficiencies in ≥2 categories. Fifteen cases (65%) were linked to process failures, 12 (52%) to human errors, eight (35%) to equipment failures, and eight (35%) to unmanaged external changes.
Conclusions and Implications for Public Health Practice: Multiple common preventable maintenance deficiencies were identified in association with disease outbreaks, highlighting the importance of comprehensive water management programs for water systems in buildings. Properly implemented programs, as described in the new industry standard, could reduce Legionella growth and transmission, preventing Legionnaires’ disease outbreaks and reducing disease.
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Introduction
Legionnaires’ disease, a severe, sometimes fatal pneumonia, can occur in persons who inhale aerosolized droplets of water contaminated with the bacterium Legionella. Exposure to Legionella in freshwater environments such as lakes and streams does not lead to disease; however, in manmade water systems, Legionella can grow and spread to susceptible hosts, including persons aged ≥50 years, smokers, and persons with underlying medical conditions such as chronic lung disease or immunosuppression.
CDC investigated the first outbreak of Legionnaires’ disease in 1976. Currently, approximately 5,000 cases of Legionnaires’ disease are reported to CDC each year; however, Legionnaires’ disease might be underdiagnosed. During 2000–2014, the rate of reported cases of legionellosis, which comprises both Legionnaires’ disease and Pontiac fever, a milder, self-limited, influenza-like illness, increased 286%, from 0.42 to 1.62 cases per 100,000 persons in the United States (1,2) (Figure 1). The reason for this increase is unknown but is likely multifactorial. The higher rates could represent a true increase in the frequency of disease related to several factors, such as a greater number of persons at risk for legionellosis because of underlying illness or immunocompromising medications, an aging U.S. population, aging plumbing infrastructure, or changes in the climate. Increased use of diagnostic testing because of greater awareness among clinicians and availability of diagnostic tests, as well as more reliable reporting to local and state health departments and CDC could also be playing a role. Approximately 9% of cases are fatal (3). Among 32 potable water–associated outbreaks reported in the United States during 2011–2012, legionellosis was implicated in 21 (66%) outbreaks and all 14 deaths (4). During 2000–2012, CDC’s Waterborne Disease and Outbreak Surveillance System received reports of approximately 160 legionellosis outbreaks (5).
Legionnaires’ disease outbreak investigations require an environmental assessment to identify potential sources of exposure. Environmental assessments are rarely conducted for Legionnaires’ disease cases that are not recognized as part of an outbreak; therefore, most of what is known about Legionella transmission has been learned from outbreak investigations. During 2005–2009, only 4% of confirmed legionellosis cases reported among U.S. residents were associated with a known outbreak or cluster (6), although some sporadic cases were likely associated with unrecognized outbreaks or clusters. Identified outbreaks generally are linked to environmental reservoirs in large or complex water systems,* such as those found in hotels or resorts, hospitals, long-term care facilities, and cruise ships. Transmission from these water systems to humans requires aerosol generation, as can occur from showerheads, cooling towers, hot tubs, and decorative fountains (7). Only one case of possible person-to-person transmission has been reported (8). Legionnaires’ disease is typically diagnosed by a Legionella urinary antigen test or culture of lower respiratory secretions using selective media; epidemiologic links to environmental sources can be confirmed when isolates from clinical and environmental specimens match by molecular typing (9). One species, Legionella pneumophila, accounts for approximately 90% of reported legionellosis cases in the United States (7).
Because Legionella transmission occurs from manmade environmental settings, the most effective strategy for prevention of Legionnaires’ disease is through control of Legionella in water systems in buildings. In 2015, ASHRAE (formerly known as the American Society of Heating, Refrigerating, and Air-Conditioning Engineers) published a consensus standard for the primary prevention of Legionnaires’ disease (10), which calls for the development and implementation of water management programs in large or complex water systems in buildings. The standard, which is based on best practices, focuses on identifying hazardous conditions and applying control measures to interrupt Legionella growth and transmission.
Outbreak investigations often find manmade water systems with maintenance gaps that permit the growth of Legionella. To identify opportunities for prevention, summaries of all CDC field investigations of outbreaks of Legionnaires’ disease during 2000–2014 were reviewed to characterize water system maintenance deficiencies leading to those outbreaks.
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Methods
CDC offers assistance to health departments with field investigations of outbreaks of Legionnaires’ disease. After each investigation, CDC reviews and summarizes the field notes to understand conditions that led to the outbreak. These summaries highlight the main findings from each investigation, including the numbers of cases and deaths, clinical or environmental strains of Legionella identified, potential or confirmed environmental sources, and possible environmental factors that contributed to the outbreak, as well as recommended solutions for the management of current outbreaks and prevention of future outbreaks.
CDC reviewed all investigation summaries and associated publications describing Legionnaires’ disease outbreak investigations conducted during 2000–2014. Investigations involving cruise ships were excluded, because their water systems are managed differently from land-based water systems. Two investigators used a standard abstraction form to review the relevant materials. Confirmed and suspected Legionnaires’ disease cases were defined using each outbreak’s case definitions; thus, slight variations in case definition among outbreaks were possible. Investigation summaries were reviewed to identify possible root causes that could facilitate Legionella growth and transmission. Each reviewer independently assigned findings to one or more of four categories: 1) process failures, in which a process, such as a water management program, was missing or inadequate; 2) human errors, in which a person did not perform as expected, such as not replacing hot tub filters according to manufacturer’s recommendations; 3) equipment failures, in which a piece of equipment did not operate as expected, such as a malfunctioning disinfectant delivery system; and 4) unmanaged external changes, in which adjustments were not made to account for events outside a building water system, such as nearby construction leading to changes in potable water quality. Discrepant categorizations were resolved through consultation with a third reviewer.
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Results
During 2000–2014, CDC participated in 38 field investigations of Legionnaires’ disease. Three investigations, determined not to be outbreaks because of lack of sufficient clinical or epidemiologic evidence, were excluded. Eight investigations involving cruise ships, associated with 19 confirmed and 17 suspected cases of Legionnaires’ disease, including two deaths, were also excluded. Among the remaining 27 investigations, 24 occurred in U.S. states and territories, two in Mexico, and one in Canada. The most frequent outbreak settings were hotels and resorts (n = 12, 44%), long-term care facilities (5, 19%), and hospitals (4, 15%) (Table 1). The remaining six outbreaks were evenly distributed among senior living facilities (n = 2, 7%), workplaces (2, 7%), and the community (2, 7%). Potable water was the most frequent source of exposure (n = 15, 56%), followed by cooling towers (6, 22%), hot tubs (2, 7%), industrial equipment (1, 4%), and a decorative fountain (1, 4%); for two outbreaks (7%), sources were not identified (Figure 2). Potable water sources accounted for 58% of travel-associated outbreaks (in hotels and resorts) and 67% of health care–associated outbreaks (in hospitals and long-term care facilities).
All 27 outbreaks were caused by Legionella pneumophila serogroup 1. Among 13 (48%) investigations (Table 1), links between human cases and water sources were established through DNA-sequence–based typing that identified indistinguishable clinical and environmental isolates. No clinical isolate was available for nine (33%) outbreaks, no environmental isolate was available for one (4%), and neither a clinical nor environmental isolate was available for two (7%); the clinical and environmental isolates did not match for the remaining two (7%) outbreaks. All available outbreak strains reacted with monoclonal antibody 2 of the international L. pneumophila serogroup 1 panel, a potential marker of increased virulence (11).
The 27 outbreaks included 415 cases, 323 (78%) of which were confirmed† and 92 (22%) suspected (Table 1). A median of 10 confirmed and suspected cases occurred in each outbreak (range = 3–82). The median number of cases in cooling tower outbreaks was 22, and in potable water outbreaks was 10. Health care–associated outbreaks accounted for 57% of all 415 cases, with a median of 19 cases per health care–associated outbreak; travel-associated outbreaks accounted for 25% of cases, with a median of seven cases per travel-associated outbreak.
Among confirmed and suspected Legionnaires’ disease cases, 65 deaths occurred; the median outbreak case fatality rate was 7% (range = 0%–80%). Health care–associated outbreaks accounted for 85% of deaths (median health care–associated outbreak case fatality rate = 24%, range = 6%–80%); travel-associated outbreaks accounted for 6% of deaths (median travel-associated outbreak case fatality rate = 0%, range = 0%–17%). Patients in seven of the nine health care–associated outbreaks included persons who were employees, visitors, or outpatients who did not stay overnight at the facility. No transplant patients were among the health care–associated cases. In 23 investigations for which the outbreak duration could be determined, the median interval from onset of the first to last cases was 49 days. Median outbreak duration was longer for potable water outbreaks (98 days) than for outbreaks linked to other sources (28 days).
Twenty-three (85%) investigation summaries had sufficient information to evaluate the contribution of deficiencies in water system maintenance to the outbreak (Table 2). The most frequent deficiencies noted were categorized as process failures (n = 15, 65%), followed by human errors (12, 52%), equipment failures (8, 35%), and unmanaged external changes (8, 35%). For 11 (48%) outbreaks, deficiencies in more than one category were reported. Sixteen (70%) investigations reported inadequate water disinfectant levels and 12 (52%) reported water temperatures in the optimal range for Legionella growth (12).§ Indications of inadequate maintenance of hot tubs and decorative fountains were almost always noted. Among the seven investigations where outbreaks were believed to be associated with unmanaged external changes, nearby construction (n = 3, 43%) and problems with water mains (3, 43%) were most frequently noted. Three buildings had water management programs (all developed before the publication of ASHRAE’s standard in 2015); however, the occurrence of outbreaks suggests that the existing water management programs were inadequate (13,14).
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Conclusions and Comments
The number of cases of Legionnaires’ disease in the United States is increasing, and associated mortality is substantial. Identifying ways to reduce environmental transmission of Legionella is crucial to reducing morbidity and mortality associated with Legionnaires’ disease. The new ASHRAE standard establishes minimum requirements for management of the risk for Legionella growth and transmission in building water systems. Gaps in maintenance that could be addressed with a water management program to prevent Legionnaires’ disease outbreaks were described in 23 (85%) of 27 investigated outbreaks. Outbreaks resulted from a combination of deficiencies, most frequently classified as process failures and human errors. In the majority of outbreaks, inadequate water disinfectant levels and temperatures in the optimal range for Legionella growth were observed; implementing a functional water management program could address these deficiencies through routine monitoring of disinfectant levels and water temperature (10). Deficiencies related to equipment failures and unmanaged external changes were less common but are also remediable through preventive measures, such as flushing of potable water systems after water main breaks. Although approximately half the outbreaks included in this analysis resulted from multiple deficiencies, approximately half resulted from a single deficiency, suggesting that even a single deficiency can be sufficient to cause an outbreak; thus, all deficiencies should be addressed.
The most frequent outbreak settings in this analysis were hotels and resorts, long-term care facilities, and hospitals. Although 44% of the outbreaks were travel-associated and 33% were health care–associated, health care–associated outbreaks were larger and resulted in more deaths than travel-associated outbreaks. Potable water was the most frequent source of exposure; however, outbreaks related to cooling tower outbreaks were associated with larger numbers of cases. This finding is consistent with the outdoor location of cooling towers and their ability to create plumes of potentially contaminated water that can expose larger numbers of persons than potable water outbreaks. Potable water outbreaks are usually associated with cases among building occupants, such as hospital patients and hotel guests. Hot tubs have been reported to be an important cause of outbreaks in hotels and cruise ships (15). Regardless of setting or source, a comprehensive approach to prevention requires an understanding of the mechanisms by which Legionella growth and transmission can occur in any building water system. Understanding the nature of deficiencies in water system maintenance using a categorization scheme such as the one described in this report can help inform plans for remediation and prevention following outbreaks of Legionnaires’ disease.
Until published by ASHRAE in 2015, consensus recommendations regarding the development of water management programs to reduce transmission of Legionella were unavailable; thus, ASHRAE’s approach to developing and implementing Legionella water management programs for water systems in buildings might be unfamiliar to building owners and managers (10). CDC and its partners have developed a toolkit (http://www.cdc.gov/legionella/WMPtoolkit) to facilitate implementation of this new standard. The multistep process begins by determining if a building is at increased risk for growth and transmission of Legionella, in which case the formation of a specialized management team is required. The toolkit guides the team through the process of identifying and controlling conditions that can permit Legionella growth and transmission in their building water systems. The process requires careful planning, frequent communication, consistent implementation, and regular review. Taking these steps should reduce the risk for Legionella growth and transmission.
The findings in this report are subject to at least three limitations. First, the scope of legionellosis encompasses Legionnaires’ disease and Pontiac fever. Because fatality is only associated with Legionnaires’ disease, prevention messages are generally targeted toward preventing Legionnaires’ disease and not Pontiac fever; therefore, the Pontiac fever cases in the five outbreaks reporting Pontiac fever (range = 1–101 cases) were excluded. Second, although understanding the clinical aspects of Legionnaires’ disease is an essential step in addressing the increasing number of reported cases, these aspects have been reported elsewhere (6,16) and are not discussed here. Finally, this analysis might not capture all possible gaps in maintenance for several reasons. CDC typically completes investigation summaries within a few weeks of an investigation and investigators might not have had access to environmental information that might have become available later. In addition, CDC does not participate in all investigations of outbreaks of Legionnaires’ disease; thus, these findings might not represent all root causes associated with outbreaks. Moreover, the outbreak-associated deficiencies described in this report might not represent root causes associated with sporadic Legionnaires’ disease cases.
Missed prevention opportunities can lead to outbreaks of Legionnaires’ disease. Making water management programs a routine part of building ownership and management will require education and reinforcement. Environmental and public health professionals can help by incorporating the ASHRAE standard into licensing and accreditation requirements, modifying building and public health codes to include water management programs, and providing tools and information to help local building owners and managers implement water management programs. Future studies should evaluate the implementation and effectiveness of water management programs in buildings with large or complex water systems. Widespread use of such programs might reduce the growth and transmission of Legionella, which, in addition to early diagnosis with appropriate clinical testing, might reduce the number and size of Legionnaires’ disease outbreaks and help reduce the occurrence of Legionnaires’ disease in the United States.
- "Legionella was implicated in 24 (57%) outbreaks, 130 (13%) cases, 109 (88%) hospitalizations, and all 13 deaths (Table 1). Eight outbreaks caused by two parasites resulted in 289 (29%) cases, among which 279 (97%) were caused by Cryptosporidium, and 10 (3%) were caused by Giardia duodenalis. Chemicals or toxins were implicated in four outbreaks involving 499 cases, with 13 hospitalizations, including the first reported outbreaks (two outbreaks) associated with algal toxins in drinking water."
- "Thirty-five (83%) outbreaks were associated with public (i.e., regulated), community or noncommunity water systems,¶ and three (7%) were associated with unregulated, individual systems. Fourteen outbreaks occurred in drinking water systems with groundwater sources and an additional 14 occurred in drinking water systems with surface water sources. The most commonly cited deficiency, which led to 24** (57%) of the 42 drinking water–associated outbreaks, was the presence of Legionella in drinking water systems"
- "All of the outbreak-associated deaths reported during this surveillance period as well as all of the outbreaks reported in hospital/health care settings or long-term care facilities, were caused by Legionella. A review of 27 Legionnaires’ disease outbreak investigations in which CDC participated during 2000–2014 identified at least one water system maintenance deficiency in all 23 investigations for which this information was available, indicating that effective water management programs in buildings at increased risk for Legionella growth and transmission (e.g., those with more than 10 stories or that house "
- "Cryptosporidium was the second most common cause of both outbreaks and illnesses, demonstrating the continued threat from this chlorine-tolerant pathogen when drinking water supplies are contaminated."
- "Legionnaires’ disease is a lung infection that is fatal for about one in 10 persons who become infected. Legionella, the bacterium that causes Legionnaires’ disease, grows well in warm water, but can be killed by disinfectants, such as chlorine. Persons can get Legionnaires’ disease when they breathe in small droplets of water contaminated with Legionella."
- "Legionella grows best in building water systems that are not well maintained, especially where levels of chlorine or other disinfectants are low and water temperatures are optimal for its growth. Legionnaires’ disease outbreaks most often occur in hotels, long-term care facilities, and hospitals. The most common sources are potable water (e.g., drinkable water used for showering), cooling towers, hot tubs, and decorative fountains."
CDC MMWR
https://www.cdc.gov/mmwr/volumes/66/wr/mm6644a3.htm?s_cid=mm6644a3_e
Surveillance for Waterborne Disease Outbreaks Associated with Drinking Water — United States, 2013–2014
Weekly / November 10, 2017 / 66(44);1216–1221
Summary
What is already known about this topic?
Waterborne disease and outbreaks associated with drinking water continue to occur in the United States. CDC collects data on waterborne disease outbreaks submitted from all states and territories through the National Outbreak Reporting System.
What is added by this report?
During 2013–2014, a total of 42 drinking water–associated outbreaks were reported to CDC, resulting in at least 1,006 cases of illness, 124 hospitalizations, and 13 deaths. Legionella was responsible for 57% of outbreaks and 13% of illnesses, and chemicals/toxins and parasites together accounted for 29% of outbreaks and 79% of illnesses. Eight outbreaks caused by parasites resulted in 289 (29%) cases, among which 279 (97%) were caused by Cryptosporidium and 10 (3%) were caused by Giardia duodenalis. Chemicals or toxins were implicated in four outbreaks involving 499 cases, with 13 hospitalizations, including the first outbreaks associated with algal toxins.
What are the implications for public health practice?
Continued public health surveillance is necessary to detect waterborne disease and monitor health trends associated with drinking water exposure. When drinking water is contaminated by infectious pathogens, chemicals, or toxins, public health agencies need to provide rapid detection, identification of the cause, and response to prevent and control waterborne illness and outbreaks. Effective water management programs in buildings at increased risk for Legionella growth and transmission can reduce the risk for disease from drinking water pathogens.
Provision of safe water in the United States is vital to protecting public health (1). Public health agencies in the U.S. states and territories* report information on waterborne disease outbreaks to CDC through the National Outbreak Reporting System (NORS) (https://www.cdc.gov/healthywater/surveillance/index.html). During 2013–2014, 42 drinking water–associated† outbreaks were reported, accounting for at least 1,006 cases of illness, 124 hospitalizations, and 13 deaths. Legionella was associated with 57% of these outbreaks and all of the deaths. Sixty-nine percent of the reported illnesses occurred in four outbreaks in which the etiology was determined to be either a chemical or toxin or the parasite Cryptosporidium. Drinking water contamination events can cause disruptions in water service, large impacts on public health, and persistent community concern about drinking water quality. Effective water treatment and regulations can protect public drinking water supplies in the United States, and rapid detection, identification of the cause, and response to illness reports can reduce the transmission of infectious pathogens and harmful chemicals and toxins.
To provide information about drinking water–associated waterborne disease outbreaks in the United States in which the first illness occurred in 2013 or 2014 (https://www.cdc.gov/healthywater/surveillance/drinking-surveillance-reports.html), CDC analyzed outbreaks reported to the CDC Waterborne Disease and Outbreak Surveillance System through NORS (https://www.cdc.gov/nors/about.html) as of December 31, 2015. For an event to be defined as a waterborne disease outbreak, two or more cases must be linked epidemiologically by time, location of water exposure, and illness characteristics; and the epidemiologic evidence must implicate water exposure as the probable source of illness. Data requested for each outbreak include 1) the number of cases, hospitalizations, and deaths; 2) the etiologic agent (confirmed or suspected); 3) the implicated water system; 4) the setting of exposure; and 5) relevant epidemiologic and environmental data needed to understand the outbreak occurrences and for determining the deficiency classification.§ One previously unreported outbreak with onset date of first illness in 2012 is presented but is not included in the analysis of outbreaks that occurred during 2013–2014.
Public health officials from 19 states reported 42 outbreaks associated with drinking water during the surveillance period (Table 1) (https://www.cdc.gov/healthywater/surveillance/drinking-water-tables-figures.html). These outbreaks resulted in at least 1,006 cases of illness, 124 hospitalizations (12% of cases), and 13 deaths. At least one etiologic agent was identified in 41 (98%) outbreaks. Counts of etiologic agents in this report include both confirmed and suspected etiologies, which differs from previous surveillance reports. Legionella was implicated in 24 (57%) outbreaks, 130 (13%) cases, 109 (88%) hospitalizations, and all 13 deaths (Table 1). Eight outbreaks caused by two parasites resulted in 289 (29%) cases, among which 279 (97%) were caused by Cryptosporidium, and 10 (3%) were caused by Giardia duodenalis. Chemicals or toxins were implicated in four outbreaks involving 499 cases, with 13 hospitalizations, including the first reported outbreaks (two outbreaks) associated with algal toxins in drinking water.
The most commonly reported outbreak etiology was Legionella (57%), making acute respiratory illness the most common predominant illness type reported in outbreaks (Table 2). Thirty-five (83%) outbreaks were associated with public (i.e., regulated), community or noncommunity water systems,¶ and three (7%) were associated with unregulated, individual systems. Fourteen outbreaks occurred in drinking water systems with groundwater sources and an additional 14 occurred in drinking water systems with surface water sources. The most commonly cited deficiency, which led to 24** (57%) of the 42 drinking water–associated outbreaks, was the presence of Legionella in drinking water systems. In addition, 143 (14%) cases were associated with seven (17%) outbreak reports that had a deficiency classification indicating “unknown or insufficient information.”
Among 1,006 cases attributed to drinking water–associated outbreaks, 50% of the reported cases were associated with chemical or toxin exposure, 29% were caused by parasitic infection (either Cryptosporidium or Giardia), and 13% were caused by Legionella infection (Table 2). Seventy-five percent of cases were linked to community water systems. Outbreaks in water systems supplied solely by surface water accounted for most cases (79%). Of the 1,006 cases, 86% originated from outbreaks in which the predominant illness was acute gastrointestinal illness. Three (7%) outbreaks in which treatment was not expected to remove the contaminant were associated with a chemical or toxin and resulted in 48% of all outbreak-associated cases.
Discussion
Water treatment processes, regulations, and rapid response to illness outbreaks continue to reduce the transmission of pathogens, reduce exposure to chemicals and toxins, and protect the public drinking water supplies in the United States. Outbreaks reported during this surveillance period include the first reports of drinking water–associated outbreaks caused by harmful algal blooms as well as the continued challenges of preventing and controlling illnesses and outbreaks caused by Legionella and Cryptosporidium. Outbreaks in community water systems caused by chemical spills (West Virginia) (2), harmful algal blooms (Ohio), Cryptosporidium (Oregon) (3), and Legionella (Michigan) demonstrated that diverse contaminants can cause interruptions in water service, illnesses, and persistent community concern about drinking water quality. Outbreaks in community water systems can trigger large and complex public health responses because of their potential for causing communitywide illness and decreasing the availability of safe water for community members, businesses, and critical services (e.g., hospitals). These outbreaks highlight the importance of public health and water utility preparedness for emergencies related to contamination from pathogens, chemicals, and toxins.
Legionella continues to be the most frequently reported etiology among drinking water–associated outbreaks (4). All of the outbreak-associated deaths reported during this surveillance period as well as all of the outbreaks reported in hospital/health care settings or long-term care facilities, were caused by Legionella. A review of 27 Legionnaires’ disease outbreak investigations in which CDC participated during 2000–2014 identified at least one water system maintenance deficiency in all 23 investigations for which this information was available, indicating that effective water management programs in buildings at increased risk for Legionella growth and transmission (e.g., those with more than 10 stories or that house susceptible populations) can reduce the risk for Legionnaires’ disease (5,6). Although Legionella was detected in drinking water, multiple routes of transmission beyond ingestion of contaminated water more likely contributed to these outbreaks, such as aerosolization from domestic or environmental sources. Cryptosporidium was the second most common cause of both outbreaks and illnesses, demonstrating the continued threat from this chlorine-tolerant pathogen when drinking water supplies are contaminated. Existing drinking water regulations and filtration systems targeted to control Cryptosporidium help protect public health in community water systems that are primarily served by surface water sources or groundwater sources under the influence of surface water (7). Through the Epidemiology and Laboratory Capacity for Infectious Diseases (ELC) Cooperative Agreement, CDC has recently begun a laboratory-based cryptosporidiosis surveillance system in the United States, CryptoNet, to better track Cryptosporidium transmission and rapidly identify outbreak sources through molecular typing (8). The cyanobacterial toxin microcystin caused the largest reported toxin contamination of community drinking water in August 2013 and September 2014 and was responsible for extensive community and water disruptions. In June 2015, the Environmental Protection Agency released specific health advisory guidance for microcystin concentrations in drinking water (9). The contamination of a community drinking water supply with 4-metholcyclohexanementanol (MCHM) also illustrates the importance of source water protection from chemicals and toxins (2).
The findings in this report are subject to at least three limitations. First, 17% of drinking water–associated outbreak reports could not be assigned a specific deficiency classification other than “unknown or insufficient information,” because of a lack of information. Furthermore, the deficiency classification most frequently reported (“presence of Legionella in drinking water systems”) does not provide insight into the specific factors contributing to Legionella amplification and transmission. Second, the detection and investigation of outbreaks might be incomplete. Because of universal exposure to water, linking illness to drinking water is inherently difficult through traditional outbreak investigation methods (e.g., case-control and cohort studies) (10). Finally, reporting capabilities and requirements vary among states and localities. Therefore, outbreak surveillance data likely underestimate actual occurrence of outbreaks and should not be used to estimate the actual number of outbreaks or cases of waterborne disease.
Public health surveillance is necessary to detect waterborne disease and outbreaks, and to continue to monitor health trends associated with drinking water exposure. Despite resource constraints, 19 states reported drinking water–associated outbreaks for 2013–2014 compared with 14 for the previous reporting period (4). In this reporting cycle, more reported outbreaks and cases were caused by parasites and chemicals than by non-Legionella bacteria, and more cases were reported from community systems than from individual systems. Most of the outbreaks and illnesses reported in this period were in community systems, which serve larger numbers of persons; outbreaks in these systems can sicken entire communities. Although individual, private water systems likely serve fewer persons than community systems, they can still result in relatively large numbers of illnesses. One outbreak reported during 2013–2014 in an individual system led to 100 estimated illnesses associated with a wedding. The public health challenges highlighted here underscore the need for rapid detection, identification of the cause, and response when drinking water is contaminated by infectious pathogens, chemicals, or toxins to prevent and control waterborne illness and outbreaks.
Acknowledgments
State, territory, and local waterborne disease coordinators, epidemiologists, and environmental health personnel; Bryanna Cikesh, Allison Miller, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC; Jessica Smith, Sooji Lee, Albert Barskey, Chris Edens, Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, CDC
MMWR
https://www.cdc.gov/mmwr/volumes/65/wr/mm6522e1.htm
Vital Signs: Deficiencies in Environmental Control Identified in Outbreaks of Legionnaires’ Disease — North America, 2000–2014
Weekly / June 10, 2016 / 65(22);576 - 584
Laurel E. Garrison, MPH1; Jasen M. Kunz, MPH2; Laura A. Cooley, MD1; Matthew R. Moore, MD1; Claressa Lucas, PhD1; Stephanie Schrag, DPhil1; John Sarisky, MPH2; Cynthia G. Whitney, MD1 (View author affiliations)
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Key Points
• Legionnaires’ disease is a lung infection that is fatal for about one in 10 persons who become infected. Legionella, the bacterium that causes Legionnaires’ disease, grows well in warm water, but can be killed by disinfectants, such as chlorine. Persons can get Legionnaires’ disease when they breathe in small droplets of water contaminated with Legionella.
• Persons most likely to get Legionnaires’ disease are those aged ≥50 years, smokers, and persons with underlying medical conditions, such as chronic lung disease or weakened immune systems.
• Legionella grows best in building water systems that are not well maintained, especially where levels of chlorine or other disinfectants are low and water temperatures are optimal for its growth. Legionnaires’ disease outbreaks most often occur in hotels, long-term care facilities, and hospitals. The most common sources are potable water (e.g., drinkable water used for showering), cooling towers, hot tubs, and decorative fountains.
• The key to preventing outbreaks is good management of building water systems, according to new industry standards. Outbreaks have occurred because of process failures (65%), human errors (52%), equipment failures (35%), external conditions (35%), or a combination of these (48%). Building owners and managers should determine if their building water systems are at increased risk for Legionella growth and spread. If so, they should develop and use a Legionella water management program according to the new industry standards (http://www.cdc.gov/legionella/WMPtoolkit).
• Additional information is available at http://www.cdc.gov/vitalsigns.
Abstract
Background: The number of reported cases of Legionnaires’ disease, a severe pneumonia caused by the bacterium Legionella, is increasing in the United States. During 2000–2014, the rate of reported legionellosis cases increased from 0.42 to 1.62 per 100,000 persons; 4% of reported cases were outbreak-associated. Legionella is transmitted through aerosolization of contaminated water. A new industry standard for prevention of Legionella growth and transmission in water systems in buildings was published in 2015. CDC investigated outbreaks of Legionnaires’ disease to identify gaps in building water system maintenance and guide prevention efforts.
Methods: Information from summaries of CDC Legionnaires’ disease outbreak investigations during 2000–2014 was systematically abstracted, and water system maintenance deficiencies from land-based investigations were categorized as process failures, human errors, equipment failures, or unmanaged external changes.
Results: During 2000–2014, CDC participated in 38 field investigations of Legionnaires’ disease. Among 27 land-based outbreaks, the median number of cases was 10 (range = 3–82) and median outbreak case fatality rate was 7% (range = 0%–80%). Sufficient information to evaluate maintenance deficiencies was available for 23 (85%) investigations. Of these, all had at least one deficiency; 11 (48%) had deficiencies in ≥2 categories. Fifteen cases (65%) were linked to process failures, 12 (52%) to human errors, eight (35%) to equipment failures, and eight (35%) to unmanaged external changes.
Conclusions and Implications for Public Health Practice: Multiple common preventable maintenance deficiencies were identified in association with disease outbreaks, highlighting the importance of comprehensive water management programs for water systems in buildings. Properly implemented programs, as described in the new industry standard, could reduce Legionella growth and transmission, preventing Legionnaires’ disease outbreaks and reducing disease.
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Introduction
Legionnaires’ disease, a severe, sometimes fatal pneumonia, can occur in persons who inhale aerosolized droplets of water contaminated with the bacterium Legionella. Exposure to Legionella in freshwater environments such as lakes and streams does not lead to disease; however, in manmade water systems, Legionella can grow and spread to susceptible hosts, including persons aged ≥50 years, smokers, and persons with underlying medical conditions such as chronic lung disease or immunosuppression.
CDC investigated the first outbreak of Legionnaires’ disease in 1976. Currently, approximately 5,000 cases of Legionnaires’ disease are reported to CDC each year; however, Legionnaires’ disease might be underdiagnosed. During 2000–2014, the rate of reported cases of legionellosis, which comprises both Legionnaires’ disease and Pontiac fever, a milder, self-limited, influenza-like illness, increased 286%, from 0.42 to 1.62 cases per 100,000 persons in the United States (1,2) (Figure 1). The reason for this increase is unknown but is likely multifactorial. The higher rates could represent a true increase in the frequency of disease related to several factors, such as a greater number of persons at risk for legionellosis because of underlying illness or immunocompromising medications, an aging U.S. population, aging plumbing infrastructure, or changes in the climate. Increased use of diagnostic testing because of greater awareness among clinicians and availability of diagnostic tests, as well as more reliable reporting to local and state health departments and CDC could also be playing a role. Approximately 9% of cases are fatal (3). Among 32 potable water–associated outbreaks reported in the United States during 2011–2012, legionellosis was implicated in 21 (66%) outbreaks and all 14 deaths (4). During 2000–2012, CDC’s Waterborne Disease and Outbreak Surveillance System received reports of approximately 160 legionellosis outbreaks (5).
Legionnaires’ disease outbreak investigations require an environmental assessment to identify potential sources of exposure. Environmental assessments are rarely conducted for Legionnaires’ disease cases that are not recognized as part of an outbreak; therefore, most of what is known about Legionella transmission has been learned from outbreak investigations. During 2005–2009, only 4% of confirmed legionellosis cases reported among U.S. residents were associated with a known outbreak or cluster (6), although some sporadic cases were likely associated with unrecognized outbreaks or clusters. Identified outbreaks generally are linked to environmental reservoirs in large or complex water systems,* such as those found in hotels or resorts, hospitals, long-term care facilities, and cruise ships. Transmission from these water systems to humans requires aerosol generation, as can occur from showerheads, cooling towers, hot tubs, and decorative fountains (7). Only one case of possible person-to-person transmission has been reported (8). Legionnaires’ disease is typically diagnosed by a Legionella urinary antigen test or culture of lower respiratory secretions using selective media; epidemiologic links to environmental sources can be confirmed when isolates from clinical and environmental specimens match by molecular typing (9). One species, Legionella pneumophila, accounts for approximately 90% of reported legionellosis cases in the United States (7).
Because Legionella transmission occurs from manmade environmental settings, the most effective strategy for prevention of Legionnaires’ disease is through control of Legionella in water systems in buildings. In 2015, ASHRAE (formerly known as the American Society of Heating, Refrigerating, and Air-Conditioning Engineers) published a consensus standard for the primary prevention of Legionnaires’ disease (10), which calls for the development and implementation of water management programs in large or complex water systems in buildings. The standard, which is based on best practices, focuses on identifying hazardous conditions and applying control measures to interrupt Legionella growth and transmission.
Outbreak investigations often find manmade water systems with maintenance gaps that permit the growth of Legionella. To identify opportunities for prevention, summaries of all CDC field investigations of outbreaks of Legionnaires’ disease during 2000–2014 were reviewed to characterize water system maintenance deficiencies leading to those outbreaks.
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Methods
CDC offers assistance to health departments with field investigations of outbreaks of Legionnaires’ disease. After each investigation, CDC reviews and summarizes the field notes to understand conditions that led to the outbreak. These summaries highlight the main findings from each investigation, including the numbers of cases and deaths, clinical or environmental strains of Legionella identified, potential or confirmed environmental sources, and possible environmental factors that contributed to the outbreak, as well as recommended solutions for the management of current outbreaks and prevention of future outbreaks.
CDC reviewed all investigation summaries and associated publications describing Legionnaires’ disease outbreak investigations conducted during 2000–2014. Investigations involving cruise ships were excluded, because their water systems are managed differently from land-based water systems. Two investigators used a standard abstraction form to review the relevant materials. Confirmed and suspected Legionnaires’ disease cases were defined using each outbreak’s case definitions; thus, slight variations in case definition among outbreaks were possible. Investigation summaries were reviewed to identify possible root causes that could facilitate Legionella growth and transmission. Each reviewer independently assigned findings to one or more of four categories: 1) process failures, in which a process, such as a water management program, was missing or inadequate; 2) human errors, in which a person did not perform as expected, such as not replacing hot tub filters according to manufacturer’s recommendations; 3) equipment failures, in which a piece of equipment did not operate as expected, such as a malfunctioning disinfectant delivery system; and 4) unmanaged external changes, in which adjustments were not made to account for events outside a building water system, such as nearby construction leading to changes in potable water quality. Discrepant categorizations were resolved through consultation with a third reviewer.
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Results
During 2000–2014, CDC participated in 38 field investigations of Legionnaires’ disease. Three investigations, determined not to be outbreaks because of lack of sufficient clinical or epidemiologic evidence, were excluded. Eight investigations involving cruise ships, associated with 19 confirmed and 17 suspected cases of Legionnaires’ disease, including two deaths, were also excluded. Among the remaining 27 investigations, 24 occurred in U.S. states and territories, two in Mexico, and one in Canada. The most frequent outbreak settings were hotels and resorts (n = 12, 44%), long-term care facilities (5, 19%), and hospitals (4, 15%) (Table 1). The remaining six outbreaks were evenly distributed among senior living facilities (n = 2, 7%), workplaces (2, 7%), and the community (2, 7%). Potable water was the most frequent source of exposure (n = 15, 56%), followed by cooling towers (6, 22%), hot tubs (2, 7%), industrial equipment (1, 4%), and a decorative fountain (1, 4%); for two outbreaks (7%), sources were not identified (Figure 2). Potable water sources accounted for 58% of travel-associated outbreaks (in hotels and resorts) and 67% of health care–associated outbreaks (in hospitals and long-term care facilities).
All 27 outbreaks were caused by Legionella pneumophila serogroup 1. Among 13 (48%) investigations (Table 1), links between human cases and water sources were established through DNA-sequence–based typing that identified indistinguishable clinical and environmental isolates. No clinical isolate was available for nine (33%) outbreaks, no environmental isolate was available for one (4%), and neither a clinical nor environmental isolate was available for two (7%); the clinical and environmental isolates did not match for the remaining two (7%) outbreaks. All available outbreak strains reacted with monoclonal antibody 2 of the international L. pneumophila serogroup 1 panel, a potential marker of increased virulence (11).
The 27 outbreaks included 415 cases, 323 (78%) of which were confirmed† and 92 (22%) suspected (Table 1). A median of 10 confirmed and suspected cases occurred in each outbreak (range = 3–82). The median number of cases in cooling tower outbreaks was 22, and in potable water outbreaks was 10. Health care–associated outbreaks accounted for 57% of all 415 cases, with a median of 19 cases per health care–associated outbreak; travel-associated outbreaks accounted for 25% of cases, with a median of seven cases per travel-associated outbreak.
Among confirmed and suspected Legionnaires’ disease cases, 65 deaths occurred; the median outbreak case fatality rate was 7% (range = 0%–80%). Health care–associated outbreaks accounted for 85% of deaths (median health care–associated outbreak case fatality rate = 24%, range = 6%–80%); travel-associated outbreaks accounted for 6% of deaths (median travel-associated outbreak case fatality rate = 0%, range = 0%–17%). Patients in seven of the nine health care–associated outbreaks included persons who were employees, visitors, or outpatients who did not stay overnight at the facility. No transplant patients were among the health care–associated cases. In 23 investigations for which the outbreak duration could be determined, the median interval from onset of the first to last cases was 49 days. Median outbreak duration was longer for potable water outbreaks (98 days) than for outbreaks linked to other sources (28 days).
Twenty-three (85%) investigation summaries had sufficient information to evaluate the contribution of deficiencies in water system maintenance to the outbreak (Table 2). The most frequent deficiencies noted were categorized as process failures (n = 15, 65%), followed by human errors (12, 52%), equipment failures (8, 35%), and unmanaged external changes (8, 35%). For 11 (48%) outbreaks, deficiencies in more than one category were reported. Sixteen (70%) investigations reported inadequate water disinfectant levels and 12 (52%) reported water temperatures in the optimal range for Legionella growth (12).§ Indications of inadequate maintenance of hot tubs and decorative fountains were almost always noted. Among the seven investigations where outbreaks were believed to be associated with unmanaged external changes, nearby construction (n = 3, 43%) and problems with water mains (3, 43%) were most frequently noted. Three buildings had water management programs (all developed before the publication of ASHRAE’s standard in 2015); however, the occurrence of outbreaks suggests that the existing water management programs were inadequate (13,14).
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Conclusions and Comments
The number of cases of Legionnaires’ disease in the United States is increasing, and associated mortality is substantial. Identifying ways to reduce environmental transmission of Legionella is crucial to reducing morbidity and mortality associated with Legionnaires’ disease. The new ASHRAE standard establishes minimum requirements for management of the risk for Legionella growth and transmission in building water systems. Gaps in maintenance that could be addressed with a water management program to prevent Legionnaires’ disease outbreaks were described in 23 (85%) of 27 investigated outbreaks. Outbreaks resulted from a combination of deficiencies, most frequently classified as process failures and human errors. In the majority of outbreaks, inadequate water disinfectant levels and temperatures in the optimal range for Legionella growth were observed; implementing a functional water management program could address these deficiencies through routine monitoring of disinfectant levels and water temperature (10). Deficiencies related to equipment failures and unmanaged external changes were less common but are also remediable through preventive measures, such as flushing of potable water systems after water main breaks. Although approximately half the outbreaks included in this analysis resulted from multiple deficiencies, approximately half resulted from a single deficiency, suggesting that even a single deficiency can be sufficient to cause an outbreak; thus, all deficiencies should be addressed.
The most frequent outbreak settings in this analysis were hotels and resorts, long-term care facilities, and hospitals. Although 44% of the outbreaks were travel-associated and 33% were health care–associated, health care–associated outbreaks were larger and resulted in more deaths than travel-associated outbreaks. Potable water was the most frequent source of exposure; however, outbreaks related to cooling tower outbreaks were associated with larger numbers of cases. This finding is consistent with the outdoor location of cooling towers and their ability to create plumes of potentially contaminated water that can expose larger numbers of persons than potable water outbreaks. Potable water outbreaks are usually associated with cases among building occupants, such as hospital patients and hotel guests. Hot tubs have been reported to be an important cause of outbreaks in hotels and cruise ships (15). Regardless of setting or source, a comprehensive approach to prevention requires an understanding of the mechanisms by which Legionella growth and transmission can occur in any building water system. Understanding the nature of deficiencies in water system maintenance using a categorization scheme such as the one described in this report can help inform plans for remediation and prevention following outbreaks of Legionnaires’ disease.
Until published by ASHRAE in 2015, consensus recommendations regarding the development of water management programs to reduce transmission of Legionella were unavailable; thus, ASHRAE’s approach to developing and implementing Legionella water management programs for water systems in buildings might be unfamiliar to building owners and managers (10). CDC and its partners have developed a toolkit (http://www.cdc.gov/legionella/WMPtoolkit) to facilitate implementation of this new standard. The multistep process begins by determining if a building is at increased risk for growth and transmission of Legionella, in which case the formation of a specialized management team is required. The toolkit guides the team through the process of identifying and controlling conditions that can permit Legionella growth and transmission in their building water systems. The process requires careful planning, frequent communication, consistent implementation, and regular review. Taking these steps should reduce the risk for Legionella growth and transmission.
The findings in this report are subject to at least three limitations. First, the scope of legionellosis encompasses Legionnaires’ disease and Pontiac fever. Because fatality is only associated with Legionnaires’ disease, prevention messages are generally targeted toward preventing Legionnaires’ disease and not Pontiac fever; therefore, the Pontiac fever cases in the five outbreaks reporting Pontiac fever (range = 1–101 cases) were excluded. Second, although understanding the clinical aspects of Legionnaires’ disease is an essential step in addressing the increasing number of reported cases, these aspects have been reported elsewhere (6,16) and are not discussed here. Finally, this analysis might not capture all possible gaps in maintenance for several reasons. CDC typically completes investigation summaries within a few weeks of an investigation and investigators might not have had access to environmental information that might have become available later. In addition, CDC does not participate in all investigations of outbreaks of Legionnaires’ disease; thus, these findings might not represent all root causes associated with outbreaks. Moreover, the outbreak-associated deficiencies described in this report might not represent root causes associated with sporadic Legionnaires’ disease cases.
Missed prevention opportunities can lead to outbreaks of Legionnaires’ disease. Making water management programs a routine part of building ownership and management will require education and reinforcement. Environmental and public health professionals can help by incorporating the ASHRAE standard into licensing and accreditation requirements, modifying building and public health codes to include water management programs, and providing tools and information to help local building owners and managers implement water management programs. Future studies should evaluate the implementation and effectiveness of water management programs in buildings with large or complex water systems. Widespread use of such programs might reduce the growth and transmission of Legionella, which, in addition to early diagnosis with appropriate clinical testing, might reduce the number and size of Legionnaires’ disease outbreaks and help reduce the occurrence of Legionnaires’ disease in the United States.
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