It is a diagnosis that doctors are usually hesitant to make, concerned they might miss any other cause and uncomfortable with 19th-century images of screaming girls, trances or collective delusions.
But Dr. Víctor Manuel Torres Meza, the director of epidemiology for the Mexico State health department, said there were some 80 documented cases from around the world. They are usually in closed communities, like schools and factories, and they tend to occur more frequently among adolescents and among girls.
The school justifies its policy as being fair to those girls whose families live far away and cannot visit them regularly.
“Yes, the girls miss their families,” Sister Cheong said. “But here we form character. A girl here is no longer an Indian girl from the mountains. She knows how to express herself, she knows how to smile. They have confidence.”