Information for Consumers and Building Owners

Legionellosis is caused by bacteria called Legionella. The disease has two different forms. Legionnaires’ disease is the more severe form of infection that causes pneumonia. Pontiac fever is caused by the same bacteria but is a milder illness without pneumonia.  For more information on Legionellosis, see the Legionellosis Fact Sheet.

The CDC has identified the following key factors internal to buildings that can lead to Legionella growth:

  • Inadequate disinfectant: does not kill or inactivate Legionella.
  • Water stagnation: Encourages biofilm growth, allows hot water to cool and cold water to warm, and reduces the level of disinfectant.
  • Water temperature: Provide conditions where Legionella grows best (77° F – 108°F)
  • Biofilm: Protects Legionella from heat and disinfectant; provides food and shelter to germs; grows on any surface that is constantly moist.
  • Scale and sediment: Uses up disinfectant and creates a protected home for Legionella and other germs.

The CDC outlines the following general activities:

  • Identify building water system for which Legionella control measures are needed.
  • Assess how much risk the conditions in those water systems pose.
  • Apply control measures to reduce the conditions, whenever possible, to prevent Legionella growth and spread.
  • Make sure the program is running as designed and is effective.

Please note that if on-site treatment is needed to reduce the growth and spread of Legionella in a building, this may result in the owner being subject to the Commonwealth of Virginia Waterworks Regulations.  If you are a building owner considering the installation of on-site treatment, please contact your ODW field office for more information.

Further information on the control of Legionella for building owners can be found at the following links:

Requirements for implementing control of Legionella have been published as follows:

Last Updated: September 18, 2024