Legionnaires’ disease is a notable problem in acute care settings. Legionnaires’ disease has been shown to be an important cause of community- and hospital-acquired pneumonia. In hospitals with Legionella colonization of the water systems, hospital-acquired legionellosis is frequently endemic, accounting for 10% to 40% of hospital-acquired pneumonias. Legionnaires’ disease also accounts for 2% to 15% of community-acquired pneumonia. In contrast, the incidence of Legionnaires’ disease in long-term care residents is not clearly delineated.