Legionnaires' disease: a rational approach to therapy.

Optimal therapy against Legionella infection is based on agents with a high intrinsic activity, an appropriate pharmacokinetic and pharmacodynamic profile (including the ability to penetrate phagocytic cells), a low incidence of adverse reactions and an advantageous cost-efficacy relationship. Newer macroazalides and fluoroquinolones are among the first-line therapies and in severe infections, particularly those occurring in immunocompromised patients, azithromycin and later fluoroquinolones are the agents of choice. Delay in the onset of adequate therapy is a key factor associated with a poor outcome. Thus, all patients with pneumonia associated with respiratory failure, shock or underlying disease causing severe immunodeficiency should initially receive an agent active against Legionella spp., at least while the aetiology remains unknown. Adjunctive measures improve outcome in critically ill patients. In intubated patients with delayed resolution, superinfection by Pseudomonas aeruginosa or co-infection caused by other pathogens should be excluded.