PALATINE, Ill. (AP) – Public health officials say they are investigating a cluster of measles cases in suburban Chicago.

The Illinois and Cook County public health departments said Thursday morning that the cluster includes five children under age 1 at KinderCare Learning Center in Palatine. Lab test confirm measles in two of the children. Test results are pending for the other three children but they have been diagnosed based on clinical and epidemiological criteria.

Officials say at this time they don’t know the source of the infection. Measles is a highly contagious respiratory disease with a characteristic rash.

Public health officials say students, staff and faculty at the facility have been notified and anyone who hasn’t been vaccinated for measles has been instructed to stay away from unvaccinated individuals for the next three weeks.