Over the past four months, doctors at Kantha Bopha Children's Hospitals in Phnom Penh have been faced with the mysterious syndrome, which kills children so fast that nearly all of those infected with it die within a day or two of being admitted to the hospital.

Dr. Beat Richner, head of the children's hospitals -- which cared for 66 patients affected by the illness, 64 of whom died -- said that no new cases of the illness had been confirmed since Saturday.

Other hospitals in the country have reported similar cases, but far fewer than the children's hospitals in the capital, which are the most popular.

In the last hours of their life, the children experienced a "total destruction of the alveola(e) in the lungs," Richner said. Alveolae are the air sacs where oxygen enters the bloodstream.

Most of the children who have contracted the illness have come from the south of the country, though health officials cannot find what is known as a cluster -- a lot of cases coming from one specific area.

By June 29, the WHO had been contacted and Cambodian officials were scrambling to instruct health providers across the country to spread information about the illness as quickly as possible.

The WHO and the Cambodian authorities' announcement of the situation drew criticism from Richner, who said they were "causing unnecessary panic."

The WHO said the unexplained nature of the outbreak obliged it to communicate the information.

Over the weekend, lab tests linked enterovirus 71 (EV71) to some of the cases. But the tests didn't solve the whole puzzle and health officials continued their investigations, noting the detection of other elements like streptococcus suis and dengue.

The link to EV71 does not particularly help in the treatment of the illness, as there is no effective antiviral treatment for severe EV71 infections and no vaccine is available.