In July–September 2015, the Illinois Department of Public Health and the Adams County Health Department investigated an outbreak of legionellosis associated with a long term care facility (LTCF). The LTCF has 43 buildings spread over 210 acres, houses around 400 residents, and offers care ranging from independent living to skilled nursing. Utility systems, including centralized hot water, are maintained by the facility.
METHODS:
Cases were categorized as confirmed or suspected Legionnaires’ disease, or as confirmed or suspected Pontiac fever. Outbreak cases required an epidemiologic link to the LTCF with an onset of symptoms after July 24, 2015. Epidemiological data were collected through interviews with patients, nurses, and facility staff using a customized questionnaire and medical chart abstraction. Environmental samples were collected from points of interest including the cooling tower and at multiple points throughout the potable water system. Initial control measures included shower restrictions in the residential building housing the first two cases and turning off all fountains. Continued control measures included implementation of water restrictions for residents and staff, and remediation of the facility’s cooling tower and potable water system. Sequence-based typing of environmental and human isolates was performed by CDC.
RESULTS:
Fifty-three confirmed cases of legionellosis were identified: 47 (87%) among facility residents and six (13%) among staff. Forty-one (77%) were confirmed Legionnaires’ disease and 12 (23%) were confirmed Pontiac fever. Twelve (23%) deaths occurred, all among residents. Cases among residents occurred in all residential buildings, and building attack rates for Legionnaires’ disease ranged from 2-17%. Staff cases worked in two residential buildings and three non-residential buildings. Molecular matches were identified between two clinical isolates obtained from autopsy specimens and multiple environmental isolates from the cooling tower and potable water system. Matched isolates were Legionella pneumophila serogroup 1, sequence type 36 (ST36). No additional cases were identified after one incubation period post-remediation of the potable water system.
CONCLUSIONS:
The distribution of cases throughout the facility grounds and the molecular matches between the clinical and environmental isolates confirmed the source of exposure as either the cooling tower and/or the potable water system. The outbreak strain, ST36, was the strain responsible for the original 1976 Legionnaires’ disease outbreak and is considered to have increased virulence potential. The facility continues to monitor for additional illness and is working to update its potable water system, which includes the building of a new permanent water treatment plant.