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Legionella

  • First recongnized in 1976 when there was an outbreak at an American Legion’s convention in Philadelphia
  • Can cause two clinical syndromes: pneumonia or “Pontiac fever”, a self-limited febrile illness
  • Relatively common cause of CAP or HAP
  • “Legionnaire’s disease is the syndrome of pna, diarrhea and fever due to legionella (really a spectrum of disease presentations)
  • clinical presentation includes mild cough (can have hemoptysis +/- CP), fever, often GI symptoms, headache
  • PE findings are non-specific, including rales on pulm exam and fever
  • Lab findings: can include leukocytosis, thrombocytopenia, transaminitis, hyponatremia (more common than in other causes of pna)
  • CXR findings are non-specific, can include focal consolidations, diffuse patchy infil., pleural effusions; can present as pulmonary nodules (or even cavitary lesions) in the immunosuppressed pt
  • Increased risk: smokers, COPD, immunosuppressed
  • Extrapulmonary infxn occur rarely (esp in immunosuppressed pts): sinusitis, cellulitis, bacteremia etc.
  • Diagnosis:
    • both urine legionella ag and respiratory culture should be sent
    • urine antigen is an EIA test, and is more sensitive than resp culture and highly specific (it will also stay positive for several days after abx)
    • urine antigen only tests for serotype 1 (causes the majority of cases in the community)

 

(Victoria Kelly MD, 11/12/10)