Seventy-five students have collapsed at a Ratanakkiri high school in a series of fainting spells over the last week that have baffled school officials and health workers.

“We don’t have a specific cause,” said Hun Sen Phoum Thmey High School Principal Thon Khun, who said the first seven students fainted on Monday and that others have fainted every day since. “We have never had such a case before.”

Provincial Health Department Director Ung Rathana attributed the fainting to lack of air circulation in the classrooms, while provincial referral hospital chief Hing Phan Sokunthea said it could be due to low blood sugar and calcium detected in the students.

However, Khun said parents suspected bad spirits. The school, located in Banlung district’s Laban Siek commune, is conducting prayer and blessing ceremonies in hopes of appeasing any angry spirits, he said.

“This place used to be a mountain and we cleared it to build the school,” Khun said. “It could have upset them.”

According to Khun, all of the students who fainted were female and most were in seventh and eighth grade.

Mass faintings of garment workers – and occasionally students – has been a phenomenon for years in Cambodia. The reasons why are not well understood, but some researchers say the fainting spells could be related to psychological stress.

In one recent study of mass faintings at garment factories, several were found to have taken place at so-called “blighted sites” known to be former Khmer Rouge killing fields or other sites of tragedy.