The rate of reported legionellosis cases has increased by nearly five and a half times since 2000. Legionella is bacteria that is naturally-occurring in fresh water aquatic systems and becomes a risk when it enters human-made water and plumbing systems. It thrives in warm water environments and is known to grow in hot tubs, spas, pools, fountains, ice machines, and faucets.

The Legionella bacteria was first discovered in 1976 in Philadelphia during an American Legion Convention. Many participants at the convention became ill with a type of pneumonia, which was later found to be caused by the respiration and inhalation of water droplets containing the Legionella bacteria.

The respiration or inhalation of water droplets or aerosols containing the bacteria can lead to community-acquired pneumonia, or Legionnaires' disease along with Pontiac Fever which is a milder form of legionellosis that presents flu-like symptoms. There are over 60 species of Legionella, with six different serogroups that can cause disease in humans but most cases of legionellosis are caused by Legionella pneumophila serogroup 1, the pneumonic form of Legionella.

Environmental Health Significance

Because Legionella is a recently-emerging environmental health issue, the resources and materials available to address the concerns presented by the bacteria are insufficient. The significant increase in reported legionellosis cases over the last two decades results in a demand for more comprehensive public and environmental health programs to target the risks associated with Legionella. In addition, further education and training for public and environmental health professionals around building water systems and premise plumbing is necessary to develop programs for preventing and mitigating these risks.

Learn More

  • Water Management Program Template, 2018 | PDF - Interactive tool to help create or improve a water management program, specifically taking into consideration Legionella control and prevention. Template works for healthcare facilities, apartment buildings, recreational water facilities, hotels, and more.
  • Preventing Legionnaires' Disease (PreventLD Training), CDC | Website
  • Water Management Program Toolkit, CDC | PDF
  • Legionella Information and fact sheets, CDC | Webpage
  • Legionella Literature Review, EPA | Webpage
  • Standard 188 – Legionellosis Risk Management, ASHRAE | Webpage
  • 2017 CMS Requirement to Reduce Legionella Risk in Health Care Facilities, Centers for Medicaid and Medicare Services | PDF