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.