More than 300 people have called health officials to report a mysterious rash that children developed after playing in a mud-filled obstacle course at a county park.
About 5,000 people attended The Mighty Mud Mania festival late last month.
Mike Williams, director of communicable disease control for St. Louis County, said health officials confirmed 23 cases of folliculitis, an inflammation of hair follicles caused by contact with certain bacteria.
Folliculitis can be caused by bacteria from soil, but Williams said the county does not know which kind of bacteria caused the outbreak.
"We may never know for sure, but it would not surprise me if this was caused by a combination of bacteria trapped in soil, mixing with water and being heated to extreme temperatures by the weather," Williams said.
Dylan Crump, 7, of Cedar Hill, woke up Thursday with clusters of small red dots on his stomach, underarms, elbows and upper lip even though his mother had taken him to see a doctor, who had prescribed an antibiotic.
Dylan and his 11-year-old brother Zach, whose rash was getting better, had gone to Mud Mania on July 29, but they won't be returning.
"I'll make my own mud pit in the backyard," said Jason Crump, the boys' father.