Five Kentucky children were being treated at Kosair Children’s Hospital on Friday for a potentially life-threatening syndrome usually caused by E. coli O157:H7 infection, and the state health department has launched an investigation into how they got sick.

“There is a cluster of children with” hemolytic uremic syndrome,” said Beth Fisher, a spokeswoman for the Kentucky Department for Public Health. “We don’t know the source at this point.”

Three of the sick children are from Hardin County, one is from Oldham County and one is from Boone County. Fisher did not know their ages, but said they are very young. All remained hospitalized Friday September 12..