LOS ANGELES, May 6 (Xinhua) -- The U.S. Centers for Disease Control and Prevention (CDC) is investigating over 100 cases of severe hepatitis in children, including five deaths, the agency said on Friday.

       The cases under investigation were found across 25 U.S. states and territories and occurred over the past seven months.

       More than 90 percent of the children were hospitalized and 14 percent required liver transplants, according to the CDC. More than half of the kids had a confirmed adenovirus infection.

       It is not yet clear what is driving these cases in young children.

       Jay Butler, the CDC's deputy director of infectious diseases, told reporters that some of the common causes of viral hepatitis had been considered, but were not found in any of the cases.

       Adenovirus has been detected in more than 50 percent of these cases, though it has not been confirmed as the actual cause, according to the CDC.