The cause of a mysterious deadly disease that has killed multiple kids in Cambodia has now been identified.

Lab tests have confirmed that EV-71, a virulent strain of the known hand, foot, and mouth disease was mostly the cause for the mysterious illness that has killed up to 52 children thus far. Of 24 samples tested, 15 were positive for EV-71.

“As far as I’m aware, EV-71 was not identified as a virus in Cambodia before,” WHO official Nima Asgari said. “We are a bit more confident. We are hoping that we can come up with something a bit more conclusive in the next day or so.”

Most of the cases have involved kids younger than 3-years-old who experienced fatal respiratory and neurological symptoms. Parents have been interviewed to identify patterns and other missing details.

Hand, foot and mouth disease is named after the telltale signs of the illness which include rashes, mouth sores and blisters covering the hands and feet. The reason the virus was not readily identified was because blisters and rashes were only reported in a number of cases. Officials are now speculating that the steroids initially adminstered by the doctors masked specific symptoms. The disease is highly infectious and is found typically in Asia; no vaccine or treatment exists. For the worst cases, the virus  can result in paralysis, brain swelling and death.

The investigation is still ongoing. Test results have also identified outlying causes which caused the other fatalities, including dengue fever (mosquito-borne) and streptococcus suis (a bacteria transmitted from pigs and causes meningitis and hearing loss when infected.)