The “undiagnosed syndrome” has killed 61 of the 62 children admitted to hospitals since April, but there’s no indication that is it spreading from person to person, said World Health Organization spokeswoman Aphaluck Bhatiasevi.

She said health workers are trying to determine whether the cases were all the same disease or a collection of various illnesses.

The children were less than 10 years old and first fell ill with a high fever, followed by neurological symptoms and severe respiratory problems that quickly progressed. The cases have been reported in hospitals in 14 provinces, with most occurring in southern Cambodia.

The statement quoted Health Minister Man Bung Heng as saying identification of the cause may take some time. It said neighboring countries have been alerted.