ID Board Review/Bacterial Diseases/Gram-negative Rods (GNR)/Legionella spp
Histology
edit- Facultative Intracellular Gram-negative bacilli
Pathophysiology
editClinical Presentations
edit- Elderly patients, classically nursing home residents
- Risk Factors: Age, Hx of COPD
- Confusion, high fever, bradycardia
- CXR often unilobar infiltrate that progresses to consolidation
- Often failure to respond to broad spectrum/appropriate antibiotics
Natural Environments
edit- Aquatic bodies e.g. lakes, streams, man-made reservoirs, standing water
- "Air conditioners in retirement homes"
Diagnosis
edit- Legionella Urine Antigen test (only detects L. pneumophila serogroup 1)
- Sputum or BAL sample for Legionella Cx
- Hyponatremia, thrombocytopenia, elevated LFTs are all suggestive
Differential Diagnoses
editManagement
edit- Proven, or suspected Legionella PNA requires either:
- Respiratory fluoroquinolone (e.g. Levofloxacin)
- Newer macrolide (e.g. Azithromycin)
NOTE: Both have good lung penetration with potent intracellular activity