Causes, How it Spreads, and People at Increased Risk
Español: Causas y transmisión
Legionella is a type of bacterium found naturally in freshwater environments, like lakes and streams. It can become a health concern when it grows and spreads in human-made building water systems like
- Showerheads and sink faucets
- Cooling towers (structures that contain water and a fan as part of centralized air cooling systems for building or industrial processes)
- Hot tubs that aren’t drained after each use
- Decorative fountains and water features
- Hot water tanks and heaters
- Large plumbing systems
Home and car air-conditioning units do not use water to cool the air, so they are not a risk for Legionella growth.
How Legionella Affects Building Water Systems and People
Learn four key steps that can lead to Legionella growing in building water systems and spreading to people.
After Legionella grows and multiplies in a building water system, water containing Legionella then has to spread in droplets small enough for people to breathe in. People can get Legionnaires’ disease or Pontiac fever when they breathe in small droplets of water in the air that contain the bacteria.
Less commonly, people can get sick by aspiration of drinking water containing Legionella. This happens when water accidently goes into the lungs while drinking. People at increased risk of aspiration include those with swallowing difficulties.
In general, people do not spread Legionnaires’ disease and Pontiac fever to other people. However, this may be possible under rare circumstances.1
Talk to your doctor or local health department if
- You believe you were exposed to Legionella
- You develop symptoms, such as fever, cough, chills, or muscle aches
Your local health department can determine whether to investigate. Be sure to mention if you spent any nights away from home in the last 10 days.
Most healthy people exposed to Legionella do not get sick. People at increased risk of getting sick are:
- People 50 years or older
- Current or former smokers
- People with a chronic lung disease (like chronic obstructive pulmonary disease or emphysema)
- People with weak immune systems or who take drugs that weaken the immune system (like after a transplant operation or chemotherapy)
- People with cancer
- People with underlying illnesses such as diabetes, kidney failure, or liver failure
- Correia AM, GonCalves J, Gomes, JP, et al. Probable Person-to-Person Transmission of Legionnaires’ Disease. N Engl J Med. 2016;374:497–8.
- Page last reviewed: April 30, 2018
- Page last updated: April 30, 2018
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