Five Kentucky children were being treated at Kosair Children’s Hospital on Friday for a potentially life-threatening syndrome usually caused by E. coli 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.”

Even though the children in this outbreak are from three different counties, officials said, they could have eaten at the same event or restaurant or eaten food that was distributed across counties.