BACKGROUND: During October and November 2015, the Chelan-Douglas Health District in Washington state identified five cases of Legionnaires’ disease (LD) among its residents, exceeding the typical report of zero or one case annually. In addition, two cases of LD were identified from neighboring Okanogan county; previously, the last Okanogan LD case was reported in 2006. Extensive case interviews revealed that the only element in common among the seven cases was that all but one had shopped at a particular grocery store in Chelan County during their exposure periods, while the seventh patient reported being near the store. As of the time of abstract submission, the investigation is ongoing, with two newly reported LD cases being interviewed.
METHODS: Exhaustive interviews were completed with cases to ascertain their activities during the exposure period. A comprehensive environmental health assessment of the implicated grocery store and the surrounding area was undertaken by Chelan-Douglas Health District. Produce misters and the associated produce display at the store were tested for Legionella by Sound Microbiology Lab, and water hoses and the misting system were replaced with ones having effective sanitation features. In addition, the store was assessed for any additional sources of water, both inside and outside the building. The Washington State Department of Health organized two conference calls for local, state and CDC officials, including CDC Legionella experts. Per CDC recommendation, assessment of other sources of aerosolized water in a quarter mile radius of the grocery store continues, including ascertainment of the presence of water features, swamp coolers and cooling towers.
RESULTS: Legionella was not detected in the environmental samples taken at the grocery store. Chelan-Douglas Health District is performing surveillance for aerosolized water in the quarter mile surrounding the implicated store, and has identified a cooling tower and several swamp coolers. In partnership with local heating, ventilating and air conditioning (HVAC) experts, Chelan-Douglas Health District is continuing to perform outreach to facilities in the community that have cooling towers and swamp coolers to emphasize effective Legionellaprevention measures.
CONCLUSIONS: While no environmental source has been definitively identified as of the time of abstract submission, this experience highlights important facets of Legionellosis cluster investigations, including the importance of performing detailed case interviews, the crucial link between epidemiologic and environmental health investigations, the importance of involving knowledgeable community members in environmental assessments, and the role of state and federal partners in providing guidance. The investigation is ongoing.