Internal Medicine

Legionnaires’ disease


Legionnaires’ disease is a form of atypical pneumonia caused by any type of Legionella bacteria.


Microsoft PowerPoint - 13-1872-Fig2
Legionnaires’ disease incidence (no. cases/100,000 population) by sex and age group, New York, New York, USA, 2002–2011. | Farnham, A., Alleyne, L., Cimini, D., & Balter, S. (2014). Legionnaires’ disease incidence and risk factors, New York, New York, USA, 2002-2011. Emerging infectious diseases, 20(11), 1795–1802. doi:10.3201/eid2011.131872


  • Man-made water reservoirs:
    • Showerheads and sink faucets
    • Hot tubs that aren’t drained after each use
    • Decorative fountains and water features
    • Hot water tanks and heaters
    • Large plumbing systems
  • No person-to-person transmission


Risk factors:

  • Old age
  • Smoking
  • Chronic lung disease
  • Poor immune function


  • Legionella pneumophila (> 90% cases)
  • OthersL. longbeachae, L. feeleii, L. micdadei, L. anisa
Transmission electron microscopy image of L. pneumophila, responsible for over 90% of Legionnaires’ disease cases | CDC (PHIL #1187) – CDC Public Health Image Library., Public Domain,

Clinical features

Incubation period: 2-10 days

Common symptoms:

  • Fever (almost all case)
  • Chills (1⁄2 cases)
  • Dry/productive cough (1⁄3 cases), shortness of breath
  • Muscle pains
  • Headaches

Other symptoms:

  • Gastrointestinal symptoms (1⁄2 cases)
    • Diarrhoea
  • Neurological symptoms (1⁄2 cases): Confusion and impaired cognition
  • Relative bradycardia
    • Low/low-normal heart rate despite the presence of a fever
Legionnaires’ disease is very similar to other types of pneumonia (lung infection), with symptoms that include cough, shortness of breath, fever, muscle aches, and headaches.


Lab investigations:

  • Urinary antigen test (DIAGNOSTIC)
  • Sputum culture


Imaging studies of 42-year-old man with severe pneumonia caused by Legionella pneumophila serogroup 11, showing lobar consolidation of the left lower lung lobe, with an air-bronchogram within the homogeneous airspace consolidation. Consensual mild pleural effusion was documented by a chest radiograph (A) and high-resolution computed tomography (B). A week after hospital admission, repeat high-resolution computerized tomography of the chest showed extensive and homogeneous consolidation of left upper and lower lobes, accompanied by bilateral ground-glass opacities (C and D). | Antonella Grottola; Comments to Author , Fabio Forghieri, Marisa Meacci, Anna Fabio, Lorena Pozzi, Patrizia Marchegiano, Mauro Codeluppi, Monica Morselli, Leonardo Potenza, Ambra Paolini, Valeria Coluccio, Mario Luppi, Fabio Rumpianesi, and Monica Pecorari – Emerging Infectious Diseases,, Public Domain,



  • Respiratory tract quinolones: Levofloxacin, moxifloxacin, gemifloxacin (5–10 days)
    • >18 years age
  • Newer macrolides: Azithromycin, clarithromycin, roxithromycin (3–5 days)
    • All ages
  • Tetracyclines: Doxycycline
    • > 12 years age

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