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

Histology Facultative Intracellular Gram-negative bacilli Pathophysiology 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 Differential Diagnoses Management 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