A World Health Organization expert says it's too early to know whether a mixture of known diseases or something new is responsible for the deaths of more than 60 children in Cambodia, AP reports.

The mystery disease has killed 61 of the 62 children hospitalized since April, but there's no indication it is spreading from person to person. Patients suffer a high fever, followed by severe respiratory problems that progress quickly. Some also experience neurological symptoms.

Dr. Nima Asgari of the WHO in Phnom Penh said Thursday, July 5 that health workers are combing through victims' records to try to determine whether the problem is a combination of known ailments or a new disease.

Most patients reported were under 7 years old and were spread across several provinces in southern and central Cambodia.