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Causes
By Mayo Clinic staffThe bacterium Legionella pneumophila is responsible for most cases of Legionnaires' disease. Outdoors, Legionella bacteria survive in soil and water, but rarely cause infections. Indoors, though, Legionella bacteria can multiply in all kinds of water systems — hot tubs, air conditioners and mist sprayers in grocery store produce departments.
Although it's possible to contract Legionnaires' disease from home plumbing systems, most outbreaks have occurred in large buildings, perhaps because complex systems allow the bacteria to grow and spread more easily.
How the infection spreads
Most people become infected when they inhale microscopic water droplets containing legionella bacteria. This might be the spray from a shower, faucet or whirlpool, or water dispersed through the ventilation system in a large building. Outbreaks have been linked to a range of sources, including:
- Hot tubs and whirlpools on cruise ships
- Cooling towers in air conditioning systems
- Decorative fountains
- Swimming pools
- Physical therapy equipment
- Water systems in hotels, hospitals and nursing homes
Scientists aren't certain how much exposure to the bacteria is needed to cause disease, but some people have developed infections after inhaling contaminated droplets for just a few minutes. And unlike many bacteria, which spread within a small radius, legionella bacteria may be capable of traveling as far as four miles through the air.
Although legionella bacteria primarily spread through aerosolized water droplets, the infection can be transmitted in other ways, including:
- Aspiration. This occurs when liquids accidentally enter your lungs, usually because you cough or choke while drinking. If you aspirate water containing legionella bacteria, you may develop Legionnaires' disease.
- Soil. A few people have contracted Legionnaires' disease after working in the garden or using contaminated potting soil. It's also possible that the disease may spread when earth containing the bacteria is stirred up at large construction sites.
- Pedro-Botet ML, et al. Epidemiology and pathogenesis of Legionella infection. http://www.uptodate.com/home/index.html. Accessed Oct. 13, 2010.
- Patient facts: Learn more about Legionnaires' disease. Centers for Disease Control and Prevention. http://www.cdc.gov/legionella/patient_facts.htm. Accessed Oct. 13, 2010.
- Edelstein PH, et al. Legionella. In: Mandell GL, et al. Mandell, Douglas, and Bennett's Principles and Practices of Infectious Diseases. 7th ed. Philadelphia, Pa.: Churchill Livingstone Elsevier; 2010. http://www.mdconsult.com/books/linkTo?type=bookPage&isbn=978-0-443-06839-3&eid=4-u1.0-B978-0-443-06839-3..00232-0. Oct. 14, 2010.
- Pedro-Botet ML, et al. Treatment and prevention of legionella infection. http://www.uptodate.com/home/index.html. Accessed Oct. 13, 2010.
- Top 10 things every clinician needs to know about legionellosis. Centers for Disease Control and Prevention. http://www.cdc.gov/legionella/top10.htm. Accessed Oct. 13, 2010.
- Pedro-Botet ML, et al. Clinical manifestations and diagnosis of legionella infection. http://www.uptodate.com/home/index.html. Accessed Oct. 13, 2010.
- Neil K, et al. Increasing incidence of legionellosis in the United States, 1990-2005: Changing epidemiologic trends. Clinical Infectious Diseases. 2008;47:591.
- Nhu Nguyen TM, et al. A community-wide outbreak of Legionnaires disease linked to industrial cooling towers — How far can contaminated aerosols spread? Journal of Infectious Diseases. 2006;193:102.
- Centers for Disease Control and Prevention, et al. Legionnaires' disease associated with potting soil — California, Oregon, and Washington, May-June 2000. MMWR. 2000;49:777. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4934a1.htm. Accessed Oct. 19, 2010.
- Legionellosis. World Health Organization. http://www.who.int/mediacentre/factsheets/fs285/en/index.html. Accessed Oct. 19, 2010.
- Sabria M, et al. Legionella infection. In: Fauci AS, et al. Harrison's Principles of Internal Medicine. 17th ed. New York, N.Y.: McGraw-Hill Medical; 2008. http://www.accessmedicine.com/content.aspx?aid=2871241. Accessed Oct. 13, 2010.
- Cunha BA. Legionnaires' disease: Clinical differentiation from typical and other atypical pneumonias. Infectious Disease Clinics of North America. 2010;24:73.
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