Legionella and immunosuppression.

Patients with defective immune systems are susceptible to Legionella infection, especially when the defect involves cell-mediated immunity. Thus, acquired immune deficiency syndrome (AIDS), corticosteroid administration, and hairy cell leukemia are risk factors for Legionellosis. Patients who have AIDS may be at risk for relapsing infections. Corticosteroid administration appears to predispose patients to simultaneous infection with multiple strains of Legionellae and development of lung abscess. Legionellosis also is found in patients who have humoral immune defects, but to a lesser extent. Thus, multiple myeloma, chronic lymphocytic leukemia, and chronic granulomatous disease have all been complicated by Legionella infection, although the risk seems to be minimal.