Legionella is one of the most frequent causes of waterborne disease (drinking water and recreational water) among humans in the United States. Below are answers to the most common questions regarding Legionella and healthy swimming.
Legionella (LEE-juh-nell-a) is a germ that can cause a type of pneumonia called legionellosis, more commonly known as Legionnaires’ disease. Legionella is microscopic, so it can’t be seen with the naked eye.
Each year, 8,000–18,000 people in the United States are hospitalized with Legionnaires’ disease. Legionnaires’ disease is usually treated successfully with antibiotics, but can sometimes be fatal.
Certain groups of people are more likely to become seriously ill when infected with Legionella:
- Individuals who are 50 years of age or older
- People with chronic lung disease
- Individuals with weakened immune systems
Legionella is not spread from one person to another.
Legionella is naturally found in water, especially warm water. Hot tubs that are not cleaned and disinfected enough can become contaminated with Legionella. A person can get infected with Legionella when they breathe in steam or mist from a contaminated hot tub.
Legionella can also be found in cooling towers, plumbing systems, and decorative pools or fountains.
Because high water temperatures make it hard to maintain the disinfectant levels needed to kill germs like Legionella, making sure that the hot tub has the right disinfectant and pH levels is essential. Here are some things you can do to determine whether a hot tub has been properly maintained:
Three Steps for Testing Hot Tub Water
- Purchase pool test strips at your local home improvement or pool supply store (be sure to check the expiration date).
- Use the test strips to check hot tub water for adequate free chlorine (2—4 parts per million [ppm]) or bromine (4—6 ppm) and pH (7.2—7.8) levels.
- If you find improper chlorine, bromine, and/or pH levels, tell the hot tub operator or owner immediately.
Four Questions to Ask Your Hot Tub Operator
- What was the most recent health inspection score for the hot tub?
- Are disinfectant and pH levels checked at least twice per day?
- Are disinfectant and pH levels checked more often when the hot tub is being used by a lot of people?
- Are the following maintenance activities performed regularly:
- Removal of the slime or biofilm layer by scrubbing and cleaning?
- Replacement of the hot tub water filter according to manufacturer’s recommendations?
- Replacement of hot tub water?
For more information about Legionella, please see CDC's Legionellosis page.
If you are a pool or hot tub operator and would like more information on how to prevent Legionella and other germs from contaminating the water, please see the Education and Information for Aquatics Staff page.