ID Board Review/Bacterial Diseases/Gram-negative Rods (GNR)/Legionella spp

Histology

 * Facultative Intracellular Gram-negative bacilli

Clinical Presentations

 * 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

 * Aquatic bodies e.g. lakes, streams, man-made reservoirs, standing water
 * "Air conditioners in retirement homes"

Diagnosis

 * Legionella Urine Antigen test (only detects L. pneumophila serogroup 1)
 * Sputum or BAL sample for Legionella Cx
 * Hyponatremia, thrombocytopenia, elevated LFTs are all suggestive

Management
NOTE: Both have good lung penetration with potent intracellular activity
 * Proven, or suspected Legionella PNA requires either:
 * Respiratory fluoroquinolone (e.g. Levofloxacin)
 * Newer macrolide (e.g. Azithromycin)