The CDC is investigating 216 reports of unusual hepatitis cases among children in the U.S. as of May 25.
The cases have occurred in 38 states and territories since October. There were 180 cases reported on May 18.
The national tally represents persons under investigation, not confirmed cases.
"This number may go up or down as CDC and states review medical charts and learn more," the CDC said.
Globally, more than 600 unusual hepatitis cases are under investigation, according to the European Center for Disease Prevention and Control. The CDC and other researchers are still investigating the cause of the hepatitis outbreak.