Update: leptospirosis and unexplained acute febrile illness among athletes participating in triathlons--Illinois and Wisconsin, 1998.

Since July 14, 1998, the Illinois Department of Health, the Wisconsin Department of Health, the U.S. Department of Agriculture (USDA), and CDC, in collaboration with other state and local health departments, have been investigating an outbreak of acute febrile illness among athletes from 44 states and seven countries who participated in triathlons in Springfield, Illinois, on June 21, 1998, and in Madison, Wisconsin, on July 5, 1998. Initial testing at CDC of specimens from four athletes identified leptospirosis as the illness in all four. This report updates the ongoing investigation of this outbreak through August 13, which indicates that Leptospira was the etiologic agent for illness in athletes and in persons with occupational or recreational exposure to Lake Springfield, where the event was held in Illinois.