PHNOM PENH, Cambodia — The investigation of a mystery disease that has killed dozens of children in Cambodia is advancing after the discovery in patient samples of a virus that causes hand, foot, and mouth disease.

The Institut Pasteur du Cambodge found enterovirus 71 in 15 of 24 patients sampled since mid-June, Philippe Buchy, head of the Phnom Penh-based institute’s virology unit, said Sunday. The virus is known to cause the symptoms seen in more than 60 children who have died across the country since April, he said.

‘‘This information is valuable and will help the investigation tremendously,’’ said Nima Asgari, leader of the emerging diseases surveillance and response group at the World Health Organization in Cambodia, working with the local Ministry of Health to review the illness.

The investigation team is reviewing cases in which the patients died before tests were done to ensure they at least clinically and epidemiologically fit the hand, foot, and mouth disease profile, Asgari said.

Preliminary findings had identified 74 cases last week, with the majority of the patients hospitalized in the Kantha Bopha Children’s Hospital in Phnom Penh. Of 66 children admitted to the hospital with similar symptoms, 64 have died, most of them between the ages of 2 and 3.