CHICAGO - Five babies at a suburban Chicago daycare center have been diagnosed with measles, adding to a growing outbreak of the disease across the United States, Illinois health officials said on Thursday. Officials are investigating the cluster of measles cases at KinderCare Learning Center in Palatine, said a statement from the Illinois and Cook County health departments. All the children are under 1 year old and would not have been subject to routine measles vaccination, which begins at 12 months.

The source of the infection was not immediately known.