The mysterious illness that killed more than 60 Cambodian children has been determined, according to medical doctors familiar with the investigation.

The World Health Organization and the Cambodian Ministry of Health concluded that a combination of disease-causing micro-organisms is to blame for the illness, according to CNN reports.

Officials from the WHO investigating the outbreak have concluded that the pathogens associated with the illness, which quickly destroys the lungs of its victims, is a combination of enterovirus 71 or "hand, foot and mouth disease", streptococcus suis, which can lead to bacterial meningitis in people who have close contact with pigs or with pork products, and dengue fever which is transmitted by mosquitos.

WHO also found that steroids, which are used to help patients by suppressing their immune system, actually worsened the illness in most of the patients, sources told CNN.

While not all the pathogenic microorganisms were found in all patients, doctors concluded that the illness was caused by their combination and exacerbated by inappropriate steroid use.

CNN reported that sources did not want to be identified because the results of the WHO investigation have not yet been released to the public. However the health organization is expected to announce shortly that area healthcare workers refrain from treating patients who exhibit symptoms of the illness with steroids.

Symptoms of the illness include severe fever, brain swelling, and difficulty breathing.

Health experts are worried that disease rates will spike because Cambodia is currently in its rainy season which is usually accompanied by an increase in the mosquito population and inadequate sanitation.

In the past four months, Cambodian doctors have been stumped with the mysterious disease that kills children so fast that nearly all those infected die within a day or two of being admitted to hospital.

Dr. Beat Richner, head of the children's hospitals in Phnom Penh, 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, according to CNN. 

Most children who have contracted the mystery disease have come from southern Cambodia, but health officials are still investigating the location of the cluster, a specific area in the country where a lot of cases are coming from.