The Illinois Department of Public Health (IDPH) announced last week that it has received reports of a total of nine patients under investigation for severe hepatitis in children under ten years of age, up from three that were reported in April.

The cases date back to January, and the most recent had the onset of symptoms in May. Two-thirds of the children tested positive for adenovirus, a common virus that typically causes cold or flulike illness. Five patients were reported in northern Illinois, two were in the western part of the state and one each was reported in the central and southern...