• A 65-year-old male presents with a 5 day history of high fever, cough, and diarrhea after returning from a 2 week cruise to the Carribean. Patient has COPD with a 30 pack-year history of cigarette smoking. Temperature is 100.2°F (39°C), respirations are 24/min, BP is 100/60mmHg, pulse is 90/min and oxygen saturation 87% on room air. Chest exam reveals dull percussion notes at the left lung base. Chest radiograph reveals left lobar infiltrate, with patchy opacities on the right. Complete metabolic panel revealed a hyponatremia of 130 mEq/L, serum creatinine of 1.0 (baseline) and elevated AST/ALT.  Complete blood count showed a leucocytosis.  A urinary antigen test was positive. Sputum culture results are being awaited, although there only neutrophils detected on Gram stain.
  • Classification
    • bacteria
      • other gram-negative
        • Legionella
          • L. pneumophila 
  • Legionnaires' disease 
    • severe atypical pneumonia
      • "fever, cough, diarrhea, especially in a smoker"
    • high fever (>39°C)
    • low heart rate
    • confusion
    • hyponatremia(<130mEq/L)
    • diarrhea
      • although no bacteria seen in GI tract
  • Pontiac fever
    • mild flu-like syndrome
  • Other etiologies of atypical pneumonia
    • Mycoplasma
    • Chlamydia
  • Typical community acquired pneumonia
    • S. pneumoniae
  • Labs are essential because clinical presentation is nonspecific, LFTs may be elevated
  • 2 most important tests
    • culture
      • weakly gram-negative
      • stain with silver instead
    • urinary antigen test
      • avoids need for sputum sample
      • remains positive even after empiric antibiotic therapy
      • available in hours vs. 3-5 days for culture
      • specific for serogroup 1 only
        • by far the most common serogroup
  • Also used
    • DFA staining of sputum
    • serology
    • PCR
  • Erythromycin, azithromycin, levofloxacin
  • Penicillin is not effective
Prognosis, Prevention and Complications
  •  Prognosis
    • good if treated promptly with antibiotics
    • worse in the immunocompromised
  • Prevention
    • routine cultures of potential water sources(e.g hospitals)
    • monochloramine disinfection of community water supplies
    • decontaminate air conditioners routinely
  • Complications
    • rare, seen more in immunocompromised patients
      • myocarditis, prosthetic valve endocarditis

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