People started getting sick about a week after the Mountain State Fair in Fletcher, near Asheville.
They believe people breathed in Legionella bacteria from mist from the bubbling water in the hot tubs inside the exposition center.
Health teams found some bacteria in a hot tub.
Investigators also found the bacteria in a sink in the women's room, but that couldn't have infected so many people.
State health teams are working with the CDC to track down the cause.