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 ˝ 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.



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. 



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.