Legionellosis is a collective term describing infection produced by Legionella spp., whereas Legionnaires disease is a multi-system illness with pneumonia. The clinical and epidemiologic aspects of these diseases (Table 1) are discussed extensively in another guideline. Although Legionnaires disease is a respiratory infection, infection-control measures intended to prevent healthcare-associated cases center on the quality of water—the principal reservoir for Legionella spp. Table 1. Clinical and epidemiologic characteristics of legionellosis/Legionnaires disease