Many facility owners and operators are unaware of the threat to their building occupants from Legionella bacteria that have colonized their water systems. This is particularly problematic in healthcare facilities where the risk of death from this bacterial pneumonia (Legionnaires’ disease) is as high as 25 percent. Studies have shown that anywhere from 20-70 percent of hospitals can be colonized with Legionella bacteria. While there are many strains of this bacteria, the most common disease-causing strain is Legionella pneumophila, serogroup 1.

Factors in these water systems that support the growth of Legionella, whether in potable or utility, include:

Temperatures Near Body Temperature
Warm water near 99°F (and between 77°F and 110°F) is more likely to support Legionella growth than cold water (at or below 68°F). Cross-connections can introduce Legionella into the potable water and can result in water temperatures that support Legionella growth.

Organic Material
Water looks clear and clean, but contains sediment (dirt) from the water distribution and treatment process. Water system disruptions, such as water main breaks or pressure changes, can increase this material and result in Legionella growth.

Other Microbes in Water
The organic material in water systems provides growth-promoting material for Legionella and other bacteria and microbes in water systems. Legionella is part of a community of microbes living in our water systems that help each other grow and survive. While most healthy people are not harmed by Legionella and these other microbes, certain immune-compromised individuals are at risk of developing Legionnaires’ disease if exposed.

What Can be Done?
Interestingly, what you need to know to prevent building-associated Legionnaires’ disease seems to arrive in the month of June. The American Society for Heating, Refrigerating and Air-conditioning Engineers (now referred to as ASHRAE) announced the final approval of the first U.S. industry standard aimed at the prevention of building-associated Legionnaires’ disease, “Legionellosis: Risk Management for Building Water Systems.” Soon after, the Centers for Disease Control and Prevention (CDC) published a water management plan toolkit in June 2016, “Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings.”

These publications by ASHRAE and CDC were preceded by a CDC publication about the rising incidence of Legionnaires’ disease in the U.S. – increasing over 200 percent in the last 10 years. This report provided details of 27 outbreak investigations conducted by the CDC from 2000-2014. The most frequent outbreak settings were hotels and resorts (44 percent), long-term care facilities (19 percent), and hospitals (15 percent). The remaining six outbreaks were evenly distributed among senior living facilities (7 percent), workplaces (7 percent), and the community (7 percent). What may surprise you is that potable water was the most frequent source of exposure (56 percent), followed by cooling towers (22 percent), hot tubs (7 percent), industrial equipment (4 percent), and a decorative fountain (4 percent); for two outbreaks (7 percent), sources were not identified. Potable water sources accounted for 67 percent of healthcare–associated outbreaks (in hospitals and long-term care facilities).

Janet E. Stout, PhD, and Jack Rihs
Janet E. Stout, PhD, president and director of the Special Pathogens Laboratory, and Jack Rihs, vice president of Laboratory Services at the Special Pathogens Laboratory

June 2017 saw one of the most dramatic developments in Legionella prevention with an announcement from the Centers for Medicare and Medicaid Services (CMS). CMS issued a policy memorandum for hospitals and long-term care facilities detailing requirements to prevent healthcare-acquired Legionnaires’ disease. As described by CMS, “This policy memorandum applies to Hospitals, Critical Access Hospitals (CAHs) and Long-Term Care (LTC). However, this policy memorandum is also intended to provide general awareness for all healthcare organizations.” The memorandum, which took effective immediately, requires facilities to develop and adhere to policies and procedures that reduce the risk of growth and spread of Legionella and other opportunistic pathogens in building water systems. CMS surveyors are to verify that facilities have:

  1. Conducted a facility risk assessment to identify where Legionella and other opportunistic waterborne pathogens could grow and spread in the facility water system.
  2. Implemented a water management program that considers the ASHRAE industry standard and the CDC toolkit, and includes control measures, such as physical controls, temperature management, disinfectant level control, visual inspections, and environmental testing for pathogens.
  3. Specified testing protocols and acceptable ranges for control measures, and documented the results of testing and corrective actions taken when control limits were not maintained.

Also in June of 2017, the CDC published another article that demonstrated that the problem of Legionnaires’ in healthcare facilities was widespread and deadly. According to the CDC:

“Legionnaires’ disease in hospitals is widespread, deadly, and preventable. These data are especially important for healthcare facility leaders, doctors, and facility managers because it reminds them to think about the risks of Legionella in their facility and to take action,” said CDC Acting Director Anne Schuchat, M.D. “Controlling these bacteria in water systems can be challenging, but it is essential to protect patients.”

This study showed that mortality for Legionnaires’ disease continues to be high – as high as 25 percent for cases acquired in the healthcare facility.

The good news is that prevention of building-associated Legionnaires’ disease is finally getting the attention it deserves. After more than 30 years advocating for prevention and working to end Legionnaires’ disease, our efforts could become a reality. Since transmission is from exposure to contaminated water, this goal is achievable by testing the water to assess the risk and then controlling the risk through engineering controls or water treatment before cases occur. For resources to explore detecting this risk and methods for control, click the “Resources” link at



  1. JE Stout, AM Goetz. Legionella pneumophila. In: APIC Text of Infection Control and Epidemiology APIC Manual. 2014, Association for Professionals in Infection Control and Epidemiology, Inc. (APIC), Washington, D.C.
  2. ANSI/ASHRAE Standard 188-2015. Legionellosis: risk management for building water systems. Atlanta (GA): ASHRAE; 2015. Also available:
  3. Centers for Disease Control and Prevention (CDC). Developing a water management program to reduce Legionella growth and spread in buildings. [internet]. Atlanta (GA):.; 2016 Jun 7. Available:
  4. Garrison LE, Kunz JM, Cooley LA, Moore MR, Lucas C, Schrag S, Sarisky J, Whitney CG. Vital Signs: deficiencies in environmental control identified in outbreaks of Legionnaires’ disease – North America, 2000-2014. MMWR Morb Mortal Wkly Rep. 2016 Jun 10;65(22):576-84. Also available: PMID: 27281485.
  5. Centers for Medicare & Medicaid Services, Center for Clinical Standards and Quality/Survey & Certification Group). Memo to State Survey Agency Directors Re: requirement to reduce Legionella risk in healthcare facility water systems to prevent cases and outbreaks of Legionnaires’ Disease (LD) [Ref: S&C 17-30 Hospitals/CAHs/NHs Revised 06.09.2017]. 2016 Jun 9.
  6. Soda, E. A., et al. (2017). Vital Signs: Health Care-Associated Legionnaires’ Disease Surveillance Data from 20 States and a Large Metropolitan Area – United States, 2015. MMWR Morb Mortal Wkly Rep 66(22): 584-589.