Editor’s note: The two sidebars in this article are exclusive to the digital edition of The Synergist. They did not appear in print.

Legionnaires’ disease is a serious but preventable illness. The rising incidence in cases over the last two decades is a critical, yet almost wholly avertible public health crisis. The state of New York and New York City were the first in the United States to implement legislation regarding the prevention of legionellosis in building water systems. These regulations focus primarily on cooling towers as the highest risk for community exposure to Legionella bacteria. Despite implementation of these regulations, reported cases of illness in New York City and the surrounding state are increasing and large-scale outbreaks continue to occur. To address the continued rise of legionellosis in the United States, it is necessary to implement regulations that include comprehensive risk assessment and management programs for building-wide water systems, including potable and non-potable sources.

ILLNESS ON THE RISE It is well known that reported cases of legionellosis, including Legionnaires’ disease and Pontiac fever, have been on the rise for the last two decades in the United States. The Centers for Disease Control and Prevention reports a 5.5-fold increase in the number of reported legionellosis cases between 2000 and 2017. In 2017 alone, 7,456 cases of legionellosis were reported as part of the agency’s National Notifiable Disease Surveillance System program. The environmental health firm PathCon Laboratories has suggested that increased risk of acquiring the illness is associated with amplification of Legionella bacteria to high concentrations in building water systems. To prevent illness, building owners and operators must control the growth of the bacteria in building water systems. Controlling bacteria growth should result in decreased risk of amplification and subsequent exposure and related illness. Legionella bacteria were discovered following the infamous 1976 outbreak at the Legionnaires’ Convention at the Bellevue-Stratford Hotel in Philadelphia, Pa. Legionella-related pneumonia is indistinguishable from other pneumonias without diagnostic testing, and it is now theorized that outbreaks occurred long before the discovery of the bacteria. Outbreaks continue to occur more than 40 years later.
AIHA: Recognition, Evaluation, and Control of Legionella in Building Water Systems (2015). ASHRAE: ANSI/ASHRAE Standard 188-2018, Legionellosis: Risk Management for Building Water Systems (August 2018). CDC: “Toolkit: Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings: A Practical Guide to Implementing Industry Standards” (PDF, June 2017). CDC Morbidity and Mortality Weekly Report: “Summary of Notifiable Diseases, United States, 2007” (July 2009). CDC Morbidity and Mortality Weekly Report: “Summary of Notifiable Diseases, United States, 2012” (July 2009). CDC WONDER: “National Notifiable Infectious Diseases and Conditions: United States” (2017).  Centers for Medicare and Medicaid Services: “Requirement to Reduce Legionella Risk in Healthcare Facility Water Systems to Prevent Cases and Outbreaks of Legionnaires’ Disease (LD)” (July 2018). EPA: “Technologies for Legionella Control in Premise Plumbing Systems: Scientific Literature Review” (September 2016). New York City Department of Health and Mental Hygiene: “Epi Data Brief: Legionnaires’ Disease in New York City, 2007 to 2017” (September 2018). PathCon Laboratories: “Technical Bulletin 1.5 – Legionella Bacteria in Environmental Samples: Hazard Analysis and Suggested Remedial Actions” (1998). The Journal of Infectious Diseases: “A Community-Wide Outbreak of Legionnaires’ Disease Linked to Industrial Cooling Towers—How Far Can Contaminated Aerosols Spread?” (January 2006). United States Census Bureau: “Annual Estimates of the Resident Population by Sex, Race, and Hispanic Origin for the United States and Counties” (2007, 2012, and 2017).
In 2017, the year for which the most current data are available from CDC, the incidence rate of legionellosis in the United States was 2.29 cases per 100,000 people compared with 1.94 cases per 100,000 people in 2015 and 1.17 cases per 100,000 people in 2012. The incidence rate for this illness is clearly following an upward trend (see Figure 1). NEW YORK REGULATIONS In the spring and summer of 2015, three distinct outbreaks of Legionnaires’ disease occurred in New York City, resulting in the emergency implementation of both state and city regulations related to the control of Legionella. The first outbreak occurred in April and May in the Flushing/Clearview area of Queens and resulted in 13 confirmed cases. No common source was identified as the cause of the outbreak. The second outbreak occurred in July in South Bronx and resulted in 113 cases of illness and 12 deaths. The New York State Department of Health performed an investigation and declared that the source of the outbreak was linked to cooling towers operated by the Concourse Plaza Hotel, Lincoln Hospital, and the Opera House Hotel. A third outbreak occurred in East Bronx in the Morris Park area during September, resulting in 15 confirmed cases and one death.
These three outbreaks were preceded by an earlier outbreak in the Bronx in January 2015. The January outbreak was linked to the Co-Op City housing development cooling towers and resulted in 12 cases of illness; however, only eight of the 12 cases identified were epidemiologically linked to Co-Op City. No fatalities were reported. In response to the summer outbreaks, the New York State Department of Health in August 2015 adopted emergency regulations for the prevention and control of Legionnaires’ disease that applied to all owners of buildings with cooling towers. The department also passed emergency regulations related to general hospitals and residential health facilities. The New York City Council passed similar emergency regulations shortly thereafter. As of 2016, the emergency regulations have been fully ratified as part of the New York Codes, Rules, and Regulations Title 10 (Volume A) Part 4; Title 24, Chapter 8 of the Rules of the City of New York; and New York City Local Law 77. The scope of the New York state regulations covers all buildings that operate cooling towers and all healthcare facilities whereas the New York City regulations are specific to cooling towers. While the New York City cooling tower regulations are more comprehensive than New York state regulations, the laws are similar and even overlap in several areas. Table 1 outlines the general similarities and differences between the state and city requirements. New York state regulations also include requirements for healthcare facilities, including performance of documented facility environmental assessments (to be updated annually); implementation of a Legionella sampling and management plan for potable water, which includes designated sampling locations, regular Legionella sampling with culture analysis, and corrective action and contingency plans; and review of the sampling plan and additional sampling as mandated by the local department of health under specific risk conditions. There are no additional requirements for healthcare facilities in the New York City laws. However, there are federal requirements set forth by the Centers for Medicare and Medicaid Services (CMS) that apply to hospitals and other healthcare facilities nationwide.
Figure 1. United States legionellosis incidence rates by state; cases per 100,000 people. Adapted from CDC WONDER and MMWR reports.
Table 1. Comparison of New York State and New York City Regulations for Legionella Prevention in Cooling Towers
Adapted from New York Codes, Rules, and Regulations Title 10 (Volume A) Part 4; Rules of the City of New York Title 24, Chapter 8; and New York City Local Law 77.
Tap on the table to open a larger version in your browser.
While the requirements of the regulations implemented by both New York state and New York City are rigorous and require extensive implementation, they are heavily weighted toward the maintenance and operation of cooling towers. While cooling tower systems have been generally designated as inherently high risk due to their operating conditions and potential for aerosol generation and drift, other water systems and equipment—including domestic hot and cold water, tempering equipment, water features, and misters—can also be designated as high risk. The only way to properly determine risk associated with any water system is to perform a risk assessment. CONTINUED CASES AND OUTBREAKS Despite implementation of these regulations, the incidence of legionellosis in New York continues to rise. In the two-year period between 2015 and 2017, the reported legionellosis incidence rate for New York state, including New York City and Upstate New York, increased from 4.49 cases per 100,000 people to 5.15 cases per 100,000 people. This equates to an increase in reported cases from 870 in 2015 to 1,022 in 2017. Since the implementation of the emergency regulations in 2015, five known outbreaks and clusters of legionellosis involving five or more cases have occurred in New York City and greater New York. The state experienced a brief hiatus in 2016 when no known large outbreaks or clusters were identified among reported cases, but three new clusters occurred in 2017 and two more outbreaks occurred in 2018. Despite rigorous testing of cooling towers by public health officials in the immediate geographic areas, no known source was identified for any of the three clusters observed in 2017. That year, local news sources reported several smaller clusters of two cases in a nursing home in Croton-on-Hudson in Westchester County, a high-rise apartment building in the Forest Hill area of Queens, and a residential building in the Rego Park area of Queens. In 2018, investigators again tested cooling towers in the immediate areas of the two reported outbreaks of legionellosis. Public health officials identified a suspected cooling tower source in the June 2018 outbreak that occurred in the Washington Heights area of Upper Manhattan; however, only six of the 27 cases associated with the outbreak demonstrated a strain match with the bacteria found in that cooling tower. A second outbreak occurred in the same Washington Heights area of the city just three months later in September and October. Investigators once again performed cooling tower testing in the immediate area, but no source was ever publicly identified. Two smaller clusters were reported in the Bronx area of New York in October 2018 that were associated with a condominium property. A small cluster was also identified at the Rikers Island prison in October. While shower heads were reportedly disinfected at the prison, no identified source was publicly released for either of the October clusters. IMPACT OF THE REGULATIONS While the New York and New York City regulations marked an unprecedented regulatory step forward for the United States in the prevention and control of legionellosis, the current laws are primarily focused on the management of cooling towers. This approach mirrors that of many public health investigations, which tend to focus on high-risk systems such as cooling towers. 
Cooling towers are certainly considered high-risk systems with respect to amplification of Legionella and other waterborne pathogens. Cooling towers use water to reject unwanted process heat using evaporation. Water is sprayed through the cooling tower to cool and evaporate. Large fans are often used to increase the evaporation rate, which creates fine mist. The fans then emit the mist from the top of the cooling tower and into the atmosphere. A paper published in The Journal of Infectious Diseases in 2006 suggests that cooling tower mists can travel up to six kilometers from their point of origin into the surrounding environment. These properties meet the criteria for high risk of Legionella amplification and exposure according to the AIHA guideline Recognition, Evaluation, and Control of Legionella in Building Water Systems. However, other building water systems can also be high risk and should be considered in regulations and guidance intended for prevention. Because the regulations focus on cooling towers, it is very possible that other important sources of potential Legionella amplification are being missed. This may explain why cases of legionellosis continue to increase in New York and New York City despite a rigorous regulatory process. Out of the five outbreaks identified in 2017 and 2018, public health agencies identified a suspected source in only one. Hundreds of sporadic cases that were never associated with an outbreak have occurred since the regulations were implemented, and the number of these cases continues to increase. Other potential explanations for the continued rise in reported cases despite implementation of the New York and New York City regulations include improved clinical testing, which allows for better diagnosis of legionellosis, and poor enforcement or poor compliance with the regulations. New York and New York City should be commended for taking legislative action in response to the 2015 legionellosis outbreaks and for setting the precedent for other states. New Orleans followed suit in 2017 with regulations focused on cooling towers that are also geared toward illness prevention. (The New Orleans regulations did not come about in response to an outbreak.) In 2015, AIHA and the American Society of Heating, Refrigerating, and Air-Conditioning Engineers published documents focused on prevention through appropriate risk assessment and identification of controls. ASHRAE’s voluntary standard, Legionellosis: Risk Management for Building Water Systems, was recently revised in 2018.  Other recent milestones for prevention include the publication of EPA’s summary document on water treatment technologies; the release of a CMS memorandum that requires the implementation of water management plans in healthcare facilities; and the publication of the CDC Toolkit, which provides practical guidance on the implementation of water management plans for healthcare facilities. While these documents have established important concepts in holistic risk assessment and control for building water systems, only the CMS memo has established a regulatory requirement for building-wide risk assessment and the development of water management practices—and only in healthcare facilities. The concept is simple: control of bacteria growth should result in reduced risk of Legionella amplification and subsequent exposure and related illness. We expect that only with continued movement toward the incorporation of building- wide risk assessment and control concepts in regulatory efforts and enforcement will the United States begin to see a downward trend in legionellosis.   MEGAN CANRIGHT, MPH, CIH, is the director of scientific operations and leader for the Water Quality practice group for Forensic Analytical Consulting Services (FACS). She was a contributing author for AIHA’s 2015 Legionella guideline. MADELEINE REBULLIDA is a project manager for FACS in Hayward, Calif., and a leader in the FACS Mold and Moisture and Northern California Water Quality practices. DAVID KAHN is a project manager for FACS in Hayward, Calif., and a leader in the FACS Northern California Water Quality practice. JOHN MARTINELLI is a principal and the healthcare practice director for FACS. He also leads the company’s Healthcare and Hazardous Building Materials practices. Send feedback to The Synergist.

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Known Legionella Outbreaks Prior to Discovery of the Bacteria in 1976 1957: 78 cases between June and August in Austin, Minn. 1965: 81 cases and 14 deaths between July and August in Washington, D.C. (St. Elizabeths Hospital) 1974: 20 cases and two deaths at the Independent Order of Oddfellows Convention in Philadelphia, Pa. (Bellevue Stratford Hotel)
Outbreaks and Clusters of Legionellosis in New York and New York City After 2015 Three known outbreaks and clusters occurred in the state of New York during 2017:  • May–June 2017: Seven cases of Legionnaires’ disease, including one death, were identified in the Lenox Hill area of Manhattan. Health inspectors investigated 116 cooling towers within a half-mile radius of the cluster area, but no source was ever publicly identified, according to The New York Times.

• October 2017: At least 14 cases of Legionnaires’ disease were reported in the Flushing area of Queens. Testing was conducted in several cooling towers. The health department ordered disinfection of some of the cooling towers but did not publicly release an identified source. 

• October 2017: Five cases of illness were reported at an assisted-living facility in the Riverdale section of the Bronx. Additional chemical treatment was provided for cooling towers, but no source was identified. 

Two known outbreaks and clusters occurred in New York state in 2018: • July 2018: Twenty-seven cases of Legionnaires’ disease, including 25 hospitalizations and one death, were reported in Upper Manhattan in the Washington Heights area. A cooling tower in the area was identified as the suspected source of the outbreak; however, only six of the 27 cases demonstrated a strain match with the bacteria identified in the cooling tower.

• September–October 2018: Twenty-nine confirmed cases of illness, including one death, were reported in the Upper Manhattan Washington Heights area, less than two months after the July 2018 outbreak in the same area. Testing was conducted in at least 20 cooling towers in the area, but no source was identified.
How Much Progress Have We Made?
Legionella Regulations  in New York
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Disadvantages of being unacclimatized:
  • Readily show signs of heat stress when exposed to hot environments.
  • Difficulty replacing all of the water lost in sweat.
  • Failure to replace the water lost will slow or prevent acclimatization.
Benefits of acclimatization:
  • Increased sweating efficiency (earlier onset of sweating, greater sweat production, and reduced electrolyte loss in sweat).
  • Stabilization of the circulation.
  • Work is performed with lower core temperature and heart rate.
  • Increased skin blood flow at a given core temperature.
Acclimatization plan:
  • Gradually increase exposure time in hot environmental conditions over a period of 7 to 14 days.
  • For new workers, the schedule should be no more than 20% of the usual duration of work in the hot environment on day 1 and a no more than 20% increase on each additional day.
  • For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% of the usual duration of work in the hot environment on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
  • The time required for non–physically fit individuals to develop acclimatization is about 50% greater than for the physically fit.
Level of acclimatization:
  • Relative to the initial level of physical fitness and the total heat stress experienced by the individual.
Maintaining acclimatization:
  • Can be maintained for a few days of non-heat exposure.
  • Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.
  • Can be regained in 2 to 3 days upon return to a hot job.
  • Appears to be better maintained by those who are physically fit.
  • Seasonal shifts in temperatures may result in difficulties.
  • Working in hot, humid environments provides adaptive benefits that also apply in hot, desert environments, and vice versa.
  • Air conditioning will not affect acclimatization.
Acclimatization in Workers