Legionnaire's Disease

Pneumonia caused by any Legionella species

Background

• Outbreaks related to exposure to colonized water
• Air travel
• Water puddles
• Excavation
• Construction sites
• Most commonly found in patients age > 50 years, smokers, immunocomprised
• Differential diagnosis often involves other atypical pneumonia and zoonotic organisms
• Requires reporting to your state's health department to help track for outbreaks

Clinical Presentation

Acute presentation of severe community acquired pneumonia (CAP)

Classic Chest X-Ray: Rapidly progressive asymmetrical patchy infiltrates

• Besides Legionella, the differential diagnosis for such a CXR finding includes:
  1. Strep pneumoniae in patients with impaired splenic function
  2. Zoonotic atypical pathogens (Q fever, tularemia, adenovirus)

Extrapulmonary organ involvement:

• CNS: Mental confusion, encephalopathic, headache
• Cardiac: Relative bradycardia
• GI: Loose stools, watery diarrhea
• Renal: Microscopic hematuria, renal insufficiency

Temperature	Appropriate HR (bpm)	Relative Bradycardia (bpm)
102°F (38.9°C)	110	< 100
103°F (39.4°C)	120	< 110
104°F (40.0°C)	130	< 120
105°F (40.6°C)	140	< 130

Classic Laboratory Findings

• Na: Low in CAP but mostly frequently associated with Legionella
• AST/ALT: Mildly increased 2-5x normal
• Phosphate: Decreased
• CK: Increased
• CRP: > 35 mg/L
• Ferritin: Increased > 2x normal

Legionella Diagnostic Triad (Cunha et al.)

Need All 3 Criteria	Key Clinical Feature	Key Lab Features (Any 3)
Signs/sx of CAP	T >102F with unexplained relative bradycardia	Hypophophatemia
New infiltrate on CXR	| Ferritin> 2x normal
No zoonotic contact hx	| Mild transaminitis
|	Relative lymphopenia

Diagnostic Test

• Urine Legionella antigen: Only detects serotypes 1-6

Antibiotic Treatment

• Macrolides: First-line agent, although a growing resistance
• Other antibiotics: Doxycycline, fluoroquinolones
• Duration of treatment: 2 weeks

References

• Cunha BA, Mickail N, Syed U, Strollo S, Laguerre M. Rapid clinical diagnosis of Legionnaires' disease during the "herald wave" of the swine influenza (H1N1) pandemic: the Legionnaires' disease triad. Heart Lung. 2010 May-Jun;39(3):249-59. [PubMed]
• Cunha BA. Legionnaires' disease: clinical differentiation from typical and other atypical pneumonias. Infect Dis Clin N Am. 2010;24(1):73-105. [PubMed]