Legionella is a type of bacterium found naturally in freshwater environments, like lakes and streams. In this environment, it rarely causes illness.

It can become a health concern when it grows and spreads in human-made water systems such as:

  • Hot tubs that aren’t maintained properly
  • Hot water tanks and heaters that aren’t kept at hot enough levels
  • Large plumbing systems, like those found in large, multi-story buildings
  • Cooling towers that are used for air conditioning in large buildings (not residential home and car air conditioning units that do not use water to cool the air)
  • Decorative fountains
  • Temporary water mains in warm weather that are not flushed regularly

This bacterium can cause a type of serious lung infection called Legionnaires’ disease, a form of pneumonia.

Once legionella grows and multiples in a building water system, that contaminated water has to spread in droplets small enough to breathe in, for example the mist given off by:

  • Hot tubs
  • Shower heads and faucets
  • Decorative fountains and water features

The most common locations associated with legionella and Legionnaires’ disease are:

  • Hospitals
  • Long-term care facilities, such as nursing homes
  • Large multi-story buildings
  • Cruise ships
  • Hotels

Those most susceptible to getting Legionnaires’ disease from legionella are:

  • Adults 50 years old or older
  • Current or former smokers
  • People with chronic lung disease such as COPD and emphysema
  • People with weakened immune systems caused by diseases such as cancer, diabetes or kidney failure
  • People who take medication that suppresses the immune system, such as chemotherapy or those taken after a transplant operation

Find out more about Legionnaires’ disease

Last Edited: August 6, 2019