In nature, L. pneumophila survives principally in water and, to a lesser extent, in soil. L. pneumophila and related Legionella species are important causes of nosocomial pneumonias. Periodic heating of water supplies to 77 C, continuous hyperchlorination, and copper-silver ionization have been shown to eradicate L. pneumophila from hospital water supplies. If hospitals cannot be decontaminated, erythromycin prophylaxis may protect high-risk immunosuppressed patients. In immunosuppressed patients, Legionnaires' disease may occasionally result from reactivation of latent organisms rather than from newly acquired infection.
Immunosuppressed patients are at particular risk.
Clinical Features Legionnaires' disease is characterized by a one-day prodrome of myalgias, malaise, and slight headache after an incubation period of two to 10 days. Acute onset of high fever, shaking chills, nonproductive cough, tachypnea, and, often, pleuritic pain ensues. The cough may subsequently become slightly productive, but the sputum is not purulent. Obtundation or toxic encephalopathy is common, but frank meningitis is not a feature. Abdominal pain, vomiting, and, especially, diarrhea may be present.