Legionella – 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 VDH – Office of Epidemiology Legionellosis webpage and Legionellosis Fact Sheet.

Despite a drinking water utility’s compliance with the Commonwealth of Virginia Waterworks Regulations, building owners may need to implement additional measures to reduce the growth and spread of Legionella within their premise plumbing. The Centers for Disease Control and Prevention (CDC) provides a questionnaire to identify buildings at risk of Legionella growth and spread.  The CDC recommends that a Legionella Water Management Plan be developed and implemented if the answer to any of these questions is “Yes”. Additionally, the CDC provides some general information in an issue of CDC Vital Signs – Legionnaire’s Disease: Use water management programs in buildings to help prevent outbreaks.

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 Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings, Version 1.1, published by 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: