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BACKGROUND: Legionella is a bacteria present in the environment and infects susceptible individuals who breathe it in as an aerosolized mist. Nosocomial infections occur when individuals acquire an infection in a healthcare setting. Nosocomial Legionella infections are of particular concern because of the vulnerable populations at risk. In May 2014, the Alabama Department of Public Health and the Jefferson County Department of Health Disease Control initiated an investigation when a legionellosis outbreak was reported in the leukemia unit of a hospital. The unit opened three months earlier on a previously unoccupied floor of the building.
METHODS: Cases were defined as individuals meeting the legionellosis case definition with at least one overnight stay on the unit. Cases were further categorized as definitely nosocomial if the individual did not leave the hospital within the 2 to 10 days prior to onset, and where otherwise possibly nosocomial. Patients were interviewed in detail about their activities and data was extracted from their medical records. Investigators also collected admission records for all patients associated with the floor and Legionella testing records for the facility. Public health staff toured the building and the potable water system's heat exchanger with recirculation, collecting samples from potential Legionella sources . CDC EPI-Aid was requested when the needed environmental sampling, testing capabilities, and Legionella expertise exceeded ADPH's capacity. Throughout the investigation, outbreak documentation was maintained on a secured server shared among pertinent state and local epidemiology, environmental, and laboratory staff.
RESULTS: Ten cases of legionellosis associated with the leukemia unit were identified; nine were inpatients and one was a visitor. Five cases were classified as definitely nosocomial. Legionella was isolated, serogroups 1 and non-1, from 35 of the initials water samples and swabs from sites in the building. Nine locations on the floor grew Legionella pneumophila serogroup 1 that was a 100% match by sequence-based typing to two patient specimens. The hospital developed and implemented mitigation and remediation efforts to remove the threat of Legionella from the water. Point-of-use filters remain in place at all sinks and showers for the unit. No new cases were identified after June 2013.
CONCLUSIONS: Epidemiologic and environmental data implicated the potable water as the source of the Legionella in this nosocomial outbreak. The building’s water system had “passed” recent environmental testing; however, when nosocomial transmission to patients is possible, there is no acceptable or "safe level" of legionellae growth in the environment.