1.1 ,This guide covers appropriate responses for employers, building owners and operators, facility managers, health and safety professionals, public health authorities, and others: (1) to a concern that a water system may be contaminated with the bacterium known as legionella (see 6.1), and (2) to the identification of one or more cases of Legionnaires' disease or Pontiac fever (see 6.3 –, 6.5). Comprehensive and explicit recommendations to limit legionella multiplication in water systems, disinfect potential sources of human exposure to legionella, and prevent health-care associated infections are beyond this guide's scope.