An illness that quickly turns deadly is claiming the lives of young patients in Cambodia. Doctors at the Kantha Bopha Children's Hospital who regularly treat conditions like Dengue fever, malaria and tuberculosis say they've never seen anything like it.

A World Health Organization representative says many of the children died within 24 hours of being admitted to the hospital. The sickness begins with a mild fever and then rapidly impairs the body. The speed of deterioration and other symptoms are baffling to medical experts.

An enterovirus associated with hand foot and mouth disease has been linked to some of the patients, but that's only one small clue and doctors aren't sure what it means. While parents try to maintain hope, medical experts are working to uncover a pattern and find more pieces to the puzzle.

CNN's Dr. Sanjay Gupta traveled to Cambodia and was granted access to the intensive care unit. See his report to learn more at 8 and 10 p.m ET on CNN.

Update: Watch Dr. Gupta's story below.