Clinical Setting

  • Community or hospital-acquired pneumonia, extrapulmonary infections (e.g., endocarditis) occur but are rare
  • Despite cough, patients with pneumonia may produce small amounts of mucoid non-purulent sputum
  • Risk factors: Immunocompromised patient, smoking, co-morbidities.
  • Associated clinical findings with pneumonia (although nonspecific):
    • Diarrhea, other gastrointestinal symptoms
    • Confusion
    • Relative bradycardia
    • Hyponatremia
    • Elevated hepatic enzymes
    • Elevated BUN and creatinine
    • Elevated ferritin levels. Range of peak levels: 591-5990 (Clin Infect Dis 46:1789, 2008)


  • Culture (requires selective media) or PCR: detects multiple serotypes.
  • Antigen assay, direct fluorescent antibody, or serology detects L. pneumophila serotype 1 strains only (for review of diagnostics see Clin Microbiol Rev 28:95, 2015).


  • Gram negative bacilli
  • Legionella pneumophila (60-80% of cases)
  • Legionella (tatlockia)   micdadei
  • Legionella wadsworthii
  • ~40 species identified, most rarely associated with human disease

Primary Regimens

  • Pneumonia
    • Levofloxacin 750 mg IV/po q24h or Moxifloxacin 400 mg IV/po q24 
    • Azithromycin 500 mg IV/po q24h 
    • No proven benefit of Rifampin combination therapy (and drug interactions are a major issue in many patients) or combination of Azithromycin + fluoroquinolone
  • Endocarditis: above (see Comments)

Alternative Regimens

Antimicrobial Stewardship

  • Duration of therapy.
    • 7-10 days of IV/po therapy depending on clinical response is appropriate for immunocompetent patients with legionella pneumonia.
    • 14-21 days of therapy with IV/po therapy depending on clinical response is recommended for immunocompromised patients.
    • Duration of therapy not well defined, but prolonged therapy, up to 5 months, has been used


  • For endocarditis
    • Advise microbiology laboratory when considering the diagnosis of Legionella spp. endocarditis as it is possible to isolate the organism in blood culture media with special handling..
    • Infectious Diseases consultation recommended
    • Several Legionella spp have been reported as causes of endocarditis.
    • Most patients reported in the literature have undergone valve replacement in addition to medical therapy.
    • Treatment recommendations based on anecdotal case reports.
    • References: J Infect 51:e256, 2005,  Clin Micro Rev 2001; 14:177, Circulation. 2015;132:1435-1486.
  • Macrolides and fluoroquinolones are probably equally effective (Clin Infect Dis 2021;72:1979).
  • TMP-SMP also probably effective but less data to support its efficacy
  • Reference on diagnosis and treatment: Infect Dis Ther. 2022; 11:973-986.

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