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Updated: Dec 23 2021

Legionnaires Disease

  • Snapshot
    • A 75-year-old woman returns from a week-long cruise with a cough and sputum production. Her family notices that she seems more confused than usual and brings her into the hospital. Earlier today, she had complained of nausea and vomiting. On physical exam, her pulse is 60/min. There are fine crackles diffusely on chest auscultation. Laboratory tests show that she has hyponatremia and mildly elevated transaminitis. A urine antigen test is positive for the suspected disease and she is started on antibiotics.
  • Introduction
    • Classification
      • Legionella pneumophila
        • an aerobic, facultative, intracellular gram - rod
      • transmission
        • aspiration of contaminated water/soil
          • air conditioning
          • hot tubs
          • swimming pools
    • Associated conditions
      • Legionnaires disease (most common)
        • lobar or insterstitial pneumonia
        • gastrointestinal and central nervous system involvement
        • more common in smokers and those with chronic lung diseases
  • Epidemiology
    • Demographics
      • more common in the elderly
    • Risk factors
      • cruise ships
      • smoking
      • immunosuppression
      • hospitalization
    • Pathogenesis
      • organism is phagocytosed into alveolar macrophages, where they replicate
      • bacterial spread occurs when they escape from macrophage vacuoles leading to host cell osmotic lysis
  • Presentation
    • Symptoms
      • cough with sputum production
      • gastrointestinal symptoms
      • nausea or vomiting
      • water diarrhea
      • central nervous system symptoms
        • confusion
        • encephalopathy
    • Physical exam
      • fever
      • altered mental status
      • dyspnea
      • relative bradycardia
      • pneumonia
  • Imaging
    • Chest radiography
      • indication
        • all patients
      • findings
        • lobar consolidation or
        • diffuse patchy infiltrates
  • Studies
    • Labs
      • urine antigen test
        • diagnostic
      • does not Gram stain well, so this requires a silver stain
      • sputum culture
        • requires special media for culture
        • charcoal yeast extract agar buffered with iron and cysteine
      • hyponatremia
      • transaminitis
    • Making the diagnosis
      • based on clinical presentation and laboratory studies
  • Differential
    • Mycoplasma pneumoniae
      • distinguishing factor
        • typically does not present with gastrointestinal or central nervous system involvement
  • Treatment
    • Medical
      • antibiotics
        • indication
          • all patients
        • drugs
          • macrolides
          • respiratory fluoroquinolones (levofloxacin and moxifloxacin)
  • Complications
    • Respiratory failure
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