Legionella sp.

Clinical Setting

• Community or hospital-acquired pneumonia, extrapulmonary infections occur but are rare.
• Risk factors: chronic lung disease, smoking, and solid organ transplant.
• See also, Legionella pneumonia, Legionella endocarditis.

Diagnosis

• 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).

Classification

• 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

• Levofloxacin 750 mg IV/po once daily OR Azithromycin 500 mg IV/po once daily 
  
• Pneumonia: See Legionella pneumonia for specific recommendations
• Endocarditis: See Legionella endocarditis for specific recommendations

Alternative Regimens

• Clarithromycin 500 mg IV/po q12h or Erythromycin 500 mg to 1 gm q6h IV/po q6h (less well tolerated and may be less effective than primary regimens) 
• Doxycycline 100 mg IV/po q12h

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.

Comments

• 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
• Most fluoroquinolones are active in vitro (Gemifloxacin, Moxifloxacin).
• Omadacycline also an alternative; ref: N Engl J Med. 2019 Feb 7; 380(6):517-527.