Background: Most cases of Legionnaires’ disease are diagnosed by the urinary antigen test (UAT). Single cases of suspected healthcare-acquired Legionnaires’ disease are often investigated by local and state health departments. Such investigations can result in disruptive and expensive interventions. We report a case of a urine-antigen–positive patient whose clinical presentation was inconsistent with Legionnaires’ disease. Within the same year, an employee at this hospital was diagnosed with presumed community-acquired Legionnaires’ disease; however, the case was considered by the health department to be healthcare acquired. The occurrence of 2 cases, as determined by the health department, fulfilled the definition for an outbreak investigation and triggered water restrictions and extensive testing of the environment and patients for Legionella. The cases and the implications of these actions are reviewed in the context of new information about false-positive urinary-antigen tests and changes to the outbreak case definitions for Legionnaires’ disease by the Council of State and Territorial Epidemiologists (CTSE). This includes “probable” cases that have no positive diagnostic tests.

Funding: None

Disclosures: Janet E. Stout reports salary from the Special Pathogens Laboratory and is an owner.