Legionella pneumophila

Snapshot

• A 60-year-old man is brought to the emergency department for confusion, cough, and diarrhea. He had recently attended a conference and stayed at an old hotel where other people reported similar symptoms. His past medical history includes chronic obstructive pulmonary disease and hypertension. He smokes 1 pack per day. On physical exam, his oxygen saturation is 92% on room air. There are fine crackles bilaterally on chest auscultation. A chest radiograph reveals diffuse patchy infiltrates. He is also found to have hyponatremia. A urine antigen test was sent for definitive diagnosis.

Introduction

• Classification
  • Legionella pneumophila
    • an aerobic, facultative, intracellular gram – rod
  • transmission
    • aspiration of contaminated water/soil
      • air conditioning
      • hot tubs
      • swimming pools
• 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
• 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
  • Pontiac fever
    • mild and flu-like without significant pulmonary involvement
• Prognosis
• Pontiac fever is self-limited

Presentation

• Symptoms 
  • Legionnaires disease
    • cough with sputum production
    • gastrointestinal symptoms
      • nausea or vomiting
      • water diarrhea
    • central nervous system symptoms
      • confusion
      • encephalopathy
  • Pontiac fever
    • malaise
    • headache
    • malaise
• Physical exam
  • fever
  • Legionnaires disease
    • 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 it 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