The Cook County Health Department has mandated all children and adults at the KinderCare Learning Center, 12404 Archer Ave., be tested for the bacteria. The day care center has been allowed remain open so the children have a place to go and not possibly carry the bacteria to other centers.
Three children associated with the outbreak - linked to a lack of handwashing - were hospitalized but have since been treated and released.
The remaining children carrying the bacteria are all under the age of 5. They, along with the adult, have been sent home along with anyone experiencing diarrhea until tests for the bacteria turn up negative twice within 24 hours.
A person who has no symptoms could still test positive for the bacteria, the department warned.
KinderCare has stepped up its efforts to sanitize the center, including adding enhanced cleaning, additional staff to monitor handwashing, and hiring a certified nurse.
The company is working with parents to reimburse them for certain out-of-pocket medical expenses and lost wages due to staying home with their children, said Beth Daniels, a spokeswoman for the day care.
"We've been doing everything possible to prevent the further spread of this," she said.