Outbreak of Legionnaire's Disease in a Rehabilitation/Assisted Living Facility Not Controlled by Conventional Methods, Davis County, Utah, 2011

BACKGROUND: Legionnaire’s Disease is a bacterial infection caused by the Legionella bacterium. Commonly found in the environment (both natural and man-made water systems), Legionella thrives in warm, stagnant water, but can also be found in soil.  Legionella pneumophilia serogroup 1 is the most common human pathogenic type; this type is detected with the Urine Antigen Test (UAT).  Utah identifies an average of 22 Legionnaire’s Disease cases a year. In January 2011, the Davis County Health Department (DCHD) received notification of two cases of Legionnaire’s Disease that resided at the same newly built and recently opened rehabilitation/assisted living facility.  The efforts to identify the potential sources of L. pneumophilia and implement control measures are described.

METHODS:  On January 7, 2011, a site visit was conducted to building plumbing errors or ‘dead legs’, identify potential water sources that may have contributed to disease transmission, and to identify additional cases. On January 10, 2011, severn water samples were taken from case rooms and resident common areas. On January 18, results from six of the seven samples came back positive for L. pneumophilia serogroup 1. DCHD and the facility implemented control measures and set up an active surveillance system for subsequent Legionnaire’s Disease cases.  The Unified State Laboratories Public Health tested all water samples for Legionella. 

RESULTS: From January 2011 – February 2011, three confirmed cases and three suspect cases were identified in the same Rehabilitation/Assisted Living facility in Davis County.  DCHD recommended conventional remediation efforts for Legionnaire’s Disease, including hyperchlorination and superheating the water system, be used to eradicate Legionella from the water system.  Follow-up water testing continued monthly for three continued months from February to April 2011.  Despite these efforts, subsequent water samples tested positive for L. pneumophilia serogroup 1.  In April 2011, one additional confirmed case and three suspect cases were identified. In April 2011, the facility installed a copper-silver ionization system.  Follow-up water samples since this system was installed were negative for L. pneumophilia serogroup 1 until September 2011, where water sampling again indicated Legionella. 

CONCLUSIONS:  DCHD worked closely with the facility on working to contain the outbreak of Legionnaire’s disease in the facility. Remediation was costly and time consuming over a four month period and the addition of an expensive method to control legionella in the water system, and subsequent positive results, indicate that eradicating Legionella from a facility water system is much harder than anticipated.