Quick book recommendation if you want to read descriptions of dozens of incidents from around the world of groups of girls around the same age that go to the same school or belong to the same convent going through the exact same thing while their parents and community leaders demand answers from the government and blame pollution, demons, or witchcraft.

OUTBREAK! The Encyclopedia of Extraordinary Social Behavior by Hilary Evans and Robert Bartholomew.

This type of thing seems to potentially happen in any group, but these group Tourette's-like symptoms are particularly frequent in institutionalized young girls under stress. If this case is typical, we'll eventually find out that the girl who started twitching first was a fairly popular or influential girl within the group and has a troubled personal history, or even actually was having some sort of seizure condition that nobody was aware of. You'll be able to connect her to every other girl because they either saw her or heard about her before showing symptoms themselves.

http://www.anomalistbooks.com/book.cfm?id=37

The authors' stated goal in compiling the book was as a reference for studying whatever it is about people that makes this happen. Pretty great bedtime reading.