Legionella pneumonia tends to be more prevalent among immunocompromised patients. Legionella pneumophila is found in ~15% (range 2-25%) of adults hospitalised for pneumonia 5.
Apart from the respiratory and inflammatory related symptoms, hyponatremia is a recognised feature due to inappropriate ADH secretion.
The infection is primarily caused by the bacteria Legionella pneumophila and, to a lesser extent, by organisms such as Tatlockia (Legionella) micdadei, Legionella bozemanii or Legionella longbeachae.
Radiographic appearances often lag behind the clinical picture there can be deterioration on imaging despite clinical improvement.
Imaging features can be variable although changes are often described as multifocal and bilateral. There may be a middle and lower zone predominance 5.
Pleural effusions can be common and are occasionally seen even in the absence of lung field infiltrates 1. Resolution of infiltrates may be slow, and the tendency for delayed clearing should be considered before initiating any further invasive diagnostic investigation.
Multilobar or multisegmental changes have been reported to be typical on CT scans 3. Described features include:
- bilateral or unilateral single or multifocal consolidative changes (most common 3) and/or ground glass opacities 2; pure ground glass changes can also uncommonly occur
- those with extensively consolidated lesions can have associated cavitation 3
- can have a subpleural or peribronchovascular pattern 2,8
Treatment and prognosis
Management is typically with antibiotics such as azithromycin 9.
History and etymology
The disease was discovered and named after an outbreak in 1976 during the American Legion convention in Philadelphia, resulting in the deaths of 29 Legionnaires 10. The bacteria Legionella pneumophila was isolated six months later by American microbiologist Joseph McDade 10.
- 1. Muder RR, Yu VL, Parry MF. The radiologic manifestations of Legionella pneumonia. Semin Respir Infect. 1988;2 (4): 242-54. Pubmed citation
- 2. Sakai F, Tokuda H, Goto H et-al. Computed tomographic features of Legionella pneumophila pneumonia in 38 cases. J Comput Assist Tomogr. 2007;31 (1): 125-31. doi:10.1097/01.rct.0000233129.06056.65 - Pubmed citation
- 3. Kim KW, Goo JM, Lee HJ et-al. Chest computed tomographic findings and clinical features of legionella pneumonia. J Comput Assist Tomogr. 2007;31 (6): 950-5. doi:10.1097/RCT.0b013e31804b211d - Pubmed citation
- 4. Meenhorst PL, Mulder JD. The chest X-ray in Legionella Pneumonia (Legionnaires' disease). Eur J Radiol. 1983;3 (3): 180-6. Pubmed citation
- 5. Reynolds JH, McDonald G, Alton H et-al. Pneumonia in the immunocompetent patient. Br J Radiol. 2010;83 (996): 998-1009. Br J Radiol (full text) - doi:10.1259/bjr/31200593 - Free text at pubmed - Pubmed citation
- 6. Godet C, Frat JP, Le Moal G et-al. Legionnaire's pneumonia: is there really an interstitial disease?. Eur J Radiol. 2007;61 (1): 150-3. doi:10.1016/j.ejrad.2006.08.020 - Pubmed citation
- 7. Yagyu H, Nakamura H, Tsuchida F et-al. Chest CT findings and clinical features in mild Legionella pneumonia. Intern. Med. 2003;42 (6): 477-82. Pubmed citation
- 8. Haroon A, Higa F, Hibiya K et-al. Organizing pneumonia pattern in the follow-up CT of Legionella-infected patients. J. Infect. Chemother. 2011;17 (4): 493-8. doi:10.1007/s10156-010-0205-y - Pubmed citation
- 9. Plouffe JF, Breiman RF, Fields BS, Herbert M, Inverso J, Knirsch C, Kolokathis A, Marrie TJ, Nicolle L, Schwartz DB. Azithromycin in the treatment of Legionella pneumonia requiring hospitalization. (2003) Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 37 (11): 1475-80. doi:10.1086/379329 - Pubmed
- 10. Henry R. Etymologia: Legionella pneumophila. (2017) Emerging Infectious Disease journal. 23(11): 1851. doi:10.3201/eid2311.ET2311