Phnom Penh, Cambodia (CNN) -- The World Health Organization, in conjunction with the Cambodian Ministry of Health, will conclude that a combination of pathogens is to blame for the mysterious illness that has claimed the lives of more than 60 children in Cambodia, medical doctors familiar with the investigation told CNN on Wednesday.
The pathogens include enterovirus 71, streptococcus suis and dengue, the medical sources said. Additionally, the inappropriate use of steroids, which can suppress the immune system, worsened the illness in a majority of the patients, they said.
The sources did not want to be identified because the results of the health organization's investigation have not yet been made public.
Dr. Beat Richner, head of Kantha Bopha Children's Hospitals -- which cared for 66 patients affected by the illness, 64 of whom died -- said that no new cases had been confirmed since last Saturday.
The World Health Organization (WHO) is also expected to advise health care workers to refrain from using steroids in patients with signs and symptoms of the infection, which include severe fever, encephalitis, and breathing difficulties.
Over the past four months, doctors at Kantha Bopha 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.
In the last hours of their life, the children experienced a "total destruction of the alveola(e) in the lungs," Richner said.
Other hospitals in the country have also reported similar cases, but far fewer than the children's hospital in the capital, which is the most popular.
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 the message to the masses as quickly as possible.
The WHO and the Cambodian authorities' announcement of the situation drew criticism from Richner, the head of the children's hospital, that 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), which is known to cause neurological disease, to some of the cases. But it didn't solve the whole puzzle and health officials continued their investigations, noting the detection of other elements like streptococcus suis and dengue.
The rainy season in Cambodia, which lasts from May to October, is a key problem in trying to control diseases like dengue, which are transmitted by mosquitoes.
Because of a lack of indoor plumbing in many homes, people collect rainwater in vats, potential breeding grounds for mosquitoes.
Streptococcus suis is a pathogen that can cause infections like bacterial meningitis in people who are in close contact with pigs or pork-products. Reported cases of it have risen significantly in recent years, notably in Southeast Asia, according to a paper that appeared last year in Emerging Infectious Diseases, a journal published by the Centers for Disease Control and Prevention (CDC) in Atlanta.
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.
In milder cases, EV71 can cause coldlike symptoms, diarrhea and sores on the hands, feet and mouth, according to the journal Genetic Vaccines and Therapy. But more severe cases can cause fluid to accumulate on the brain, resulting in polio-like paralysis and death.
Outbreaks of the enterovirus "occur periodically in the Asia-Pacific region," according to the CDC. Brunei had its first major outbreak in 2006. China had an outbreak in 2008.
Adults' well-developed immune systems usually can fend off the virus, but children are vulnerable to it, according to the CDC.
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.
CNN's Sara Sidner and Tim Schwarz contributed to this report