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Health Department

About Legionella

What is Legionella?

Legionella is a naturally occurring bacterium that is found in low concentrations in freshwater aquatic environments such as lakes and streams.  Legionella becomes a health concern when it infiltrates into building water systems, finds a suitable condition in which to multiply and becomes aerosolized.  Examples of problematic building systems include:

Legionnaire’s disease

Legionnaire’s disease (LD) is a serious type of pneumonia (lung infection) that is contracted after breathing in water that has been contaminated with LegionellaLegionella can also cause a less severe illness referred to as Pontiac Fever.  

Most healthy people who are exposed to Legionnaire’s disease do not become sick. Being 50 years or older or having certain risk factors increases your chances of becoming sick. These include:

  • Being a current or former smoker
  • Having chronic lung disease like chronic obstructive pulmonary disease (COPD) or emphysema
  • Having a weakened immune system due to cancer, diabetes or kidney failure
  • Taking medication that weakens the immune system, such as chemotherapy.

If you develop pneumonia-type symptoms and believe you have been exposed to Legionella, see your doctor. Symptoms of Legionnaire’s disease include:

  • Cough
  • Muscle Aches
  • Fever
  • Shortness of Breath
  • Headache

Doctors will use chest x-rays, physical exams and possibly urine or phlegm to test for pneumonia. It can be treated with antibiotics. Most people, who are diagnosed, will need hospitalization but will make a full recovery. However 1 in 10 people will die from the infection.

What are we doing?

Legionnaire’s disease (LD) and Pontiac fever are notifiable diseases; therefore, your doctor is required to report all confirmed cases.  All cases that appear to have originated in Nashville/Davidson County are routed to Metro Public Health Department for case review.  If you or your doctor has reported a case of Legionnaire’s disease, you may or may not be contacted by an investigator seeking further information about your case.  All cases are reviewed to determine whether this is an isolated case or if this is part of a larger outbreak.

Surveillance and Reporting (Centers for Disease Control)

Cooling Tower Registration

Cooling towers are a heat rejection device commonly accompanying HVAC systems for larger buildings. A cooling tower uses air flow to cool water stored in its reservoir to reduce heat in the building. In this exchange, heat and evaporated water are expelled out the top of the cooling tower in a cloud like mist.  If cooling towers are not routinely cleaned and disinfected, they are a suitable environment for Legionella to grow.  If this happens, one cooling tower has the potential to be a source of an outbreak covering a large area depending on location and weather patterns.

The Metro Public Health Department developed a registry of cooling towers in Nashville/Davidson County. Registration is completely voluntary. The purpose of the registration is to collect data on all new and existing towers to better respond to a potential outbreak of Legionnaire’s disease.

If you are a building owner and wish to provide registry information for one or more cooling towers, download the Cooling Tower Registry document and submit the completed form to You will be added to our mailing list and be supplied with educational material on cooling towers and creating a water management plan.


Hotels typically contain large plumbing systems with certain parts of the plumbing becoming stagnant when portions of the hotel are not used routinely.  These lines are referred to as “dead legs.”  These stagnant lines are perfect breeding grounds for bacterium such as Legionella.

Metro Public Health Department works with hotel owners to educate on the importance of water management to curb the growth of Legionella throughout the premise plumbing. Key aspects of an effective water management plan include:

  • Describing the water systems
  • Identifying potential problem areas
  • Deciding on control measures and monitoring methods
  • Determining control limits and responses to exceedances
  • Validation of program effectiveness
  • Documentation of activities

Construction Related Articles

Pools and Hot Tubs/Spas

Pools, and hot tubs recirculate water throughout the body of water that has been disinfected and filtered. When the recirculation system has not been sized correctly or maintained, the body of water can become contaminated with Legionella.

The Metro Public Health Department reviews plans for all public pools built in Davidson County. Once plans are approved, public pools are inspected during construction and then monthly after opening to ensure compliance.

Approval Process for Public Pools in Nashville/Davidson County (Metro Public Health Department)