Legionellosis Outbreak Associated with a Hotel Fountain—Chicago, 2012

BACKGROUND:  Legionnaires’ disease (LD), an often-severe pneumonia, and Pontiac Fever (PF), a milder flu-like illness, are caused by environmental exposure to Legionella bacteria. Sporadic LD cases have increased during the past 10 years and outbreaks with high case counts of LD and PF are atypical. In August 2012, the Chicago Department of Public Health (CDPH) was notified of 30 individuals with respiratory illness and one fatality among ~600 employees of Company A who stayed at a Chicago hotel during July 26-August 3. Suspecting LD, CDPH advised the hotel to close their swimming pool, spa, and decorative lobby fountain and began an investigation.

METHODS:  Case finding included notifying ~8500 hotel guests with stays during July 16-August 15, press releases, an Epi-X notice, and media interviews. CDPH operated a call center during the investigation. A standardized questionnaire assessing illness and exposures was sent electronically to Company A employees and administered to call center callers. Case definitions were consistent with CSTE’s clinical description and laboratory criteria for legionellosis; cases included confirmed and suspect LD, and PF. For the exposure analysis, cases were compared to 196 asymptomatic hotel guests using the Mantel-Haenszel Chi-Square test. Illinois Department of Public Health assessed the building water system, reviewed maintenance logs, and sampled water sources. CDC performed sequence-based typing on environmental and clinical isolates.

RESULTS:  One hundred and fourteen cases were identified: 11 confirmed LD, 29 suspect LD, and 74 PF cases. Illness onsets occurred July 21-August 22. Median age was 48 years (range 22-82 years), 64% were male, 59% sought medical care (15 hospitalizations), and three died. Relative risks for hotel exposures revealed that persons who spent time near the lobby fountain or bar were respectively 2.16 (95%Confidence Interval (CI): 1.66,2.80) and 1.25 (95%CI: 1.09,1.44) times more likely to become ill than those who did not. L. pneumophila serogroup 1 (Lp1) was isolated from samples collected from the fountain, spa, and women’s locker room fixtures. Lp1 environmental isolates and a clinical isolate had matching sequence-based types.

CONCLUSIONS:  Environmental testing identified Legionella in the hotel’s potable water system.  The epidemiologic and molecular typing data confirmed that the fountain was likely the source. Building water systems were upgraded to include chlorine dioxide treatment and require ongoing maintenance and monitoring to reduce conditions that favor Legionella growth and transmission. Poor fountain maintenance likely created favorable conditions for Legionella overgrowth, resulting in a point-source outbreak of LD and PF cases.