LEGIONELLA

Historical: Legionaire’s dz first described in 1976 American Legion convention in Philadelphia hotel.

Epidemiology: 2-15% of all com-acq pneumon req hospitalization. (top 3-4 bugs) Only 3% correctly dxd. Legionella pheumonia more likely to be severe by VS and CXR, more likely to req ICU. RISK FACTORS: cig smoking, chronic lung dz, immunosuppression (esp. steroids), surgery (esp transplant).

MODE OF TRANSMISSION: inhalation of aerosols (cooling towers, respiratory therapy equip, whirlpool baths) or microaspiration of contaminated water (head and neck surg, NG tubes).

Virulence factors: 40 species, less than ½ cause dz in humans. L pneumophila most virulent (90% of cases). 14 serogroups, serogroup 1 accounts for > 80% of cases. Flagella linked w/ virulence.

Clnical Manifestations: Broad spectrum of illness from mild cough and low-grade fever to stupor, resp and multi-organ failure. Early sxs non-specific: fever, malaise, myalgias, anorexia, HA. T often > 40. Cough slightly productive sometimes hemoptysis. CP, sometimes pleuritic. GI sxs: watery diarrhea 20-40%. CV: relative bradycardia. FEN: Hyponatremia (Na < 130). Extrapulm: myocarditis, pericarditis, postcardiotomy synd, prosthetic valve endocarditis, sinusitis, cellulitis, pancreatitis, peritonitis, pyelo.

Labs:

1. Cx: most definitive. Charcoal-yeast extract medium. Many labs do not cx properly. Sputum cx may be revealing regardless of quality of specimen.

2. DFA: sensitivity < cx. Monoclonal test superior.

3. Legionella Urinary Antigen: Sens 70%, Spec 100%. Sens improved by ultrafiltration of urine. Remains positive for weeks on abx. Less than 10% positive after 60 days post rx. Only detects serogroup 1.

4. Serologic tests: 4-fold increase in convalescent titers. Must include IgM and IgG.

5. PCR: Highly specific, no more senstitive than cx.

6. Pleural fluid: send for cx and LUA.

Treatment:

1. Erythro- historical drug of choice

2. Azithro- greater intracellular and lung penetration.

3. Quniolones- annecdotal support, esp cipro.

4. Rifampin- rec in combination w/ macrolide or quinolone in severly ill pts.

5. Tetracycline, imipenem. Bactrim, oflox, clinda reported.