Between January 6-8, 2017, six adults spent time at a vacation rental house in Walker, Minnesota. All six had spent time in the home's pool area, which included a swimming pool, hot tub, and sauna. Two individuals were urine antigen positive for Legionella pneumophila (LP) serogroup 1 and thus, were confirmed Legionnaires' Disease (LD) cases. One other person met the case definition for a probable case of LD. This case developed symptoms early in the morning on January 8, and was diagnosed with pneumonia but tested negative by urine antigen. The remaining 3 individuals met the case definition for Pontiac Fever. All of the cases developed symptoms within 2 days of their first exposure to the pool area. Two cases were hospitalized. No one died.

Water quality tests conducted by a Minnesota Department of Health (MDH) sanitarian revealed levels all outside the state regulatory limits. The timing of exposure to the spa pool which was improperly disinfected and maintained, suggested that inhalation of aerosols from the spa pool was the most likely source of infection. As a result of the outbreak, the pool and spa pool were no longer available for use by renters.