Legionella

• First recongnized in 1976 when there was an outbreak at an American Legion’s convention in Philadelphia
• Can cause two clinical syndromes: pneumonia or “Pontiac fever”, a self-limited febrile illness
• Relatively common cause of CAP or HAP
• “Legionnaire’s disease is the syndrome of pna, diarrhea and fever due to legionella (really a spectrum of disease presentations)
• clinical presentation includes mild cough (can have hemoptysis +/- CP), fever, often GI symptoms, headache
• PE findings are non-specific, including rales on pulm exam and fever
• Lab findings: can include leukocytosis, thrombocytopenia, transaminitis, hyponatremia (more common than in other causes of pna)
• CXR findings are non-specific, can include focal consolidations, diffuse patchy infil., pleural effusions; can present as pulmonary nodules (or even cavitary lesions) in the immunosuppressed pt
• Increased risk: smokers, COPD, immunosuppressed
• Extrapulmonary infxn occur rarely (esp in immunosuppressed pts): sinusitis, cellulitis, bacteremia etc.
• Diagnosis:
• both urine legionella ag and respiratory culture should be sent
• urine antigen is an EIA test, and is more sensitive than resp culture and highly specific (it will also stay positive for several days after abx)
• urine antigen only tests for serotype 1 (causes the majority of cases in the community)

(Victoria Kelly MD, 11/12/10)