Legionella pneumophila

Legionella 

• Characteristics
  • Gram negative rod
    • Gram stains poorly, and will often show neutrophils with no bacteria inside
  • Best visualized with silver stain 
  • Grows on charcoal yeast extract medium with iron and cysteine
  • Facultative intracellular
    • This is relatively high yield, as cell-mediated (T-cell) immunity is important in clearing the bacteria
• Aerosol transmission from contaminated water sources
  • E.g. air conditioning systems, hot water tanks
  • Usually affects groups of people sharing a water reservoir (e.g. cruise ships)
  • No person-to-person transmission
• Presentation
  • Legionnaires’ disease
    • Increased risk in smokers (chronic lung disease) or immunocompromised individuals
    • Severe pneumonia (often unilateral and lobar)
    • High fever
      • Fever can often exceed 103 C
    • GI symptoms
      • Nausea or vomiting 
      • Watery diarrhea
    • CNS symptoms
      • Contrast with Mycoplasma pneumoniae, which does not present w GI or CNS involvement 
      • Confusion 
      • Encephalopathy 
    •  Labs may show hyponatremia
      • May have relative bradycardia on physical exam 
  • Pontiac fever
    • Milder version of disease with flu-like symptoms
    • Seen in healthy people
• Diagnosis
  • Urine antigen test
• Treatment
  • Macrolide or respiratory fluoroquinolone (levoquinolone)