Phnom Penh, Cambodia (CNN) -- Before dawn, the line of parents trying to comfort their sick children stretched around the Kantha Bopha Children's Hospital in Cambodia's capital, Phnom Penh.
Dozens of children waited their turn for treatment. It is the normal daily routine here, especially during the rainy season when mosquito-borne illnesses are most prevalent.
But over the past four months doctors inside the busy hospital have been faced with something that is not routine at all; a mysterious syndrome killing children so fast nearly all of the children infected with it die within a day or two of being admitted to the hospital.
Other hospitals in the country also began reporting similar cases -- though far fewer than the children's hospital in the capital, which is the most popular. Since April, doctors at the Kantha Bopha hospital have reported 66 cases of the illness. Of those cases only two children survived, while 64 died.
Most of the children who have contracted the illness have come from south of the country, though health officials cannot find what is known as a cluster -- that is a lot of cases coming from one specific area.
"We have no evidence there are particular places where this is more likely to occur. So it is really a different pattern from a normal infectious epidemic where you have a cluster of cases. This does not follow that pattern," the World Health Organization's representative in Cambodia, Pieter van Maaren, told CNN.
By June 29, The WHO had been contacted and Cambodian Health officials were scrambling to instruct health providers across the country to spread the message to the masses as quickly as possible.
On Sunday, the head of pediatrics was in the hospital surrounded by children hooked up to intravenous drips. A five-year-old howled with stomach pain, while another child was too lethargic to lift his head. Most of the children were feverish and dehydrated.
Dr. Te Vantha darted from one sick child to another trying to make sure they were getting the treatment they needed. Nurses hurried in and out with syringes and medicines. Meanwhile, mothers stroked their children's heads, their faces blank from tiredness or wrinkled in worry.
At this time of year, about 50 children per day are brought to the hospital for treatment. Usually their ailments are treatable but in the past four months Dr. Vantha said he has seen two cases that have left him baffled. In both cases the children's condition deteriorated alarmingly fast.
In one child the "lung X-ray on the right side showed consolidated opacity. The right lung had been destroyed," he said.
"There was rapid evolution from hour to hour."
That child died within 24 hours of being admitted to his hospital. The other died within 48 hours.
He said their symptoms included difficulty breathing, high fever and coughing. He has been telling any parent he can that if a child has similar symptoms to rush them to hospital.
In Cambodia, as with many places around the world, parents first try treating their child at home. If that doesn't work then they go to their local clinic, with a trip to the nearest hospital the last resort as it often involves a long trip.
That is exactly what the family of five-year-old Pov Roath did. They waited a week before bringing him to the hospital after trying their local clinic first. Nor Nim, his grandmother, sat beside him in the intensive care unit as he gasped for air and held his stomach. Nurses hurriedly put an oxygen tube in his nose to try to make it easier for him to breathe.
Dr. Vantha examined him as the boy vacillated between yelping in pain and struggling to breathe.
Eventually little Roath was diagnosed with Dengue fever. An estimated 10,000 Cambodians have contracted Dengue fever so far this year, authorities say. Some 45 people have died from it. It is a nasty illness but its mortality rate here is far lower than that of the current mystery illness.
Roath's grandmother was relieved because by the time she got to the hospital, she had heard of the mystery illness that had taken so many children's lives.
"I heard about it on television. It's terrible," she said.
But many other parents -- even those lining up at the main children's hospital -- had yet to hear of it.
"I did not know [about the new disease]," Yin Penh said, as she waited in the long line outside the Kantha Bopha Hospital with her eight-year-old daughter. "I just know my daughter has a fever and is vomiting."
Doctors at that hospital said children age three and younger seem to be most at risk, but one child as old as 11 had contracted the mystery illness.
Lab tests have revealed a link that may explain or at least get health providers a step closer to solving the mystery. Of 24 samples tested, 15 came back positive for EV71, a known Enterovirus associated with hand foot and mouth disease, that is also known to cause neurological disease.
The most recent outbreaks have been in Asia but none has been reported in Cambodia until now. But health officials warn it does not explain why the illness is taking lives so quickly, or why it hasn't spread faster as EV71 is highly contagious. There is no known cure or treatment for EV71.
The WHO representative made clear the tests at this point have not solved the mystery of the unnamed illness. More tests are being done at laboratories.
In the meantime the government is trying to make the public aware. Some are getting the message.
Eam Srey brought her four-year-old son to the hospital as soon as she noticed his fever and blood in his stool.
She clutched him on her lap and put a cold compress on his forehead while she waited to get into the hospital.
"I am very worried that my son might have the new disease," she said.
Her only comfort is her son doesn't have all the symptoms, so she is hopeful he will be treated and released.
The wait to find out is agonizing.
CNN's Tim Schwarz contributed to this report.