- Legionnaires’ disease was named for an epidemic of lower respiratory tract disease at the 1976 American Legion convention in Philadelphia. The previously unrecognized causative bacterium was isolated, identified, and named Legionella pneumophila. The organism primarily causes pneumonia and flulike illness. Legionella preferentially colonizes commercial water systems (e.g., hotels, hospitals, apartment buildings, air conditioning cooling towers).
- It is one of the three most common causes of pneumonias and the most common atypical pneumonia.
- System(s) affected: pulmonary, gastrointestinal (GI)
- Synonym(s): Legionella pneumonia; legionellosis; Pontiac fever (self-limited flulike illness without pneumonia caused by Legionella species)
- Predominant age: 15 months to 84 years; 74–91% of patients are >50 years old.
- Predominant gender: male > female
Etiology and Pathophysiology
- L. pneumophila is a weak gram-negative aerobic saprophytic freshwater bacterium. It is widely distributed in soil and water. Bipolar flagella provide motility; grow optimally at 40–45°C
- Exists in nature as a protozoan parasite, often within fresh water biofilms
- Serogroups 1 to 6 account for clinical disease.
- Serogroup 1 represents 70–92% of all clinical cases of Legionella in the United States.
- In the lung, Legionella infects alveolar macrophages.
- The organism is transmitted by breathing in contaminated water droplets or by aspiration of contaminated water (e.g., contaminated shower water was responsible for the inaugural Philadelphia outbreak).
- Community outbreaks have been associated with whirlpools, spas, fountains, and aboard cruise ships.
- Impaired cellular immunity (Legionella are intracellular pathogens.)
- Male gender
- Smoking; alcohol abuse
- Immunosuppression; HIV; diabetes; organ transplant recipients; chronic or high-dose corticosteroid use
- Chronic cardiopulmonary disease
- Advanced age
- Use of antimicrobials within the past 3 months
- Not transmitted person to person (Respiratory isolation is unnecessary.)
- Superheat and flush water systems: Heat water to at least 70°C and flush for 30 minutes (2)[C].
- Ultraviolet light and coppersilver ionization are bactericidal.
- Monochloramine disinfection of municipal water supplies decreases risk for Legionella infection.
- 0.2 micron water filters—must change regularly
- Keep water heaters >60°C, cold water <20°C.
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Domino, Frank J., et al., editors. "Legionnaires' Disease." 5-Minute Clinical Consult, 27th ed., Wolters Kluwer, 2020. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688507/1.3/Legionnaires'_Disease.
Legionnaires' Disease. In: Domino FJF, Baldor RAR, Golding JJ, et al, eds. 5-Minute Clinical Consult. Wolters Kluwer; 2020. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688507/1.3/Legionnaires'_Disease. Accessed June 4, 2023.
Legionnaires' Disease. (2020). In Domino, F. J., Baldor, R. A., Golding, J., & Stephens, M. B. (Eds.), 5-Minute Clinical Consult (27th ed.). Wolters Kluwer. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688507/1.3/Legionnaires'_Disease
Legionnaires' Disease [Internet]. In: Domino FJF, Baldor RAR, Golding JJ, Stephens MBM, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2020. [cited 2023 June 04]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688507/1.3/Legionnaires'_Disease.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Legionnaires' Disease ID - 1688507 ED - Domino,Frank J, ED - Baldor,Robert A, ED - Golding,Jeremy, ED - Stephens,Mark B, BT - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688507/1.3/Legionnaires'_Disease PB - Wolters Kluwer ET - 27 DB - Medicine Central DP - Unbound Medicine ER -