Legionnaires' disease in Las Vegas: A 7-year saga

Legionnaires' disease (LD) is a severe pneumonia acquired by inhalation of water containing Legionella bacteria. In October, 2008, CDC notified the Southern Nevada Health District of 2 recent Legionnaires' disease cases among guests of Facility A, a hotel/timeshare in Las Vegas, NV, and the site of an outbreak in 2001-2002. An investigation was conducted to determine the source and prevent ongoing transmission.

Biofilm and 1-liter water samples were taken from the potable water system, cooling towers, and public bathing places and cultured for Legionella. Sequence-based typing (SBT) was used to compare 2008 environmental isolates to 2001-2002 isolates. Additional case finding included written notification of guests staying from August 2008-January 2009 and administration of a standardized questionnaire. A case was defined as a guest who developed clinical signs of pneumonia within 2 to 10 days of a stay at Facility A with laboratory evidence of LD.

Seven confirmed cases were identified with onset dates between October, 2007-2008; all cases occupied rooms served by the same hot water loop. Sampling revealed Legionella pneumophila serogroup 1 in water taken from all guest room towers despite the presence of chlorine dioxide generators, which had been installed in 2002 to prevent Legionella growth. Environmental isolates in 2008 were identical to 2001-2002 clinical and environmental isolates by SBT.

This extended contamination period highlights the complexity of Legionella remediation for large water systems, the value of increased national surveillance for LD, and the importance of continued communication and cooperation between affected facilities and public health officials.