"There's a great idea that what has brought on the PANDAs is an environmental issue and the school, they were saying, they did air quality testing within the school but it's like they almost have a refusal to go out and test the soil," Clark said. "We also know with the gas wells and the residue, there's a holding tank, maybe, and it's come out on the ground and killed neighboring trees and plants."
An investigation by the New York Department of Health found "no evidence of environmental or infection as the cause of the girls' illness," according to department spokesman Jeffrey Hammond. "The school is served by a public water system. ... An environmental exposure would affect many people."
Several hundred community members, parents and students gathered for a town meeting on Saturday at which the school announced that it had hired a private firm to conduct an additional round of air quality tests at the school in hopes of reassuring anxious residents.
"What I have to do as the superintendent is take what the experts are telling me, and what the experts are telling me and what the data is showing me is that there is no environment case here linked to this condition," the school's superintendent, Kim Cox, told meeting attendees.
The possibility of an environmental trigger has been bolstered by reports of similar symptoms in two teens living in Corinth, a town 250 miles from Le Roy. The girls started showing symptoms in May, around the same time they passed through Le Roy on their way to a softball tournament in Ohio. At least one has since been diagnosed with Tourette's Syndrome.
Meanwhile, the National Institutes of Health has stepped in to offer to help solve the medical puzzle. Dr. Mark Hallett, chief of the NIH Medical Neurology Branch, said the cluster of cases offers a unique research opportunity.
"We have offered our help but have not been asked for it yet [by individual patients]," said Hallett, adding that he has not yet seen any of the teens. "One of the difficulties in this is that there hasn't been a lot of attention to this problem or very much research into it, which has made it somewhat of a mysterious disorder."
Hallett said conversion disorder is common, affecting as many as two people at his movement disorders clinic each week. But he said it's rare to see a large group of people with the same symptoms.
"We don't understand that aspect of it completely," Hallett said of the potential for conversion disorder to spread through a group, a characteristic that once earned it the name "mass hysteria." "For some reason, the brain mimics things that they know. ... It's just one of the ways the brain reacts to psychological stress. We don't understand why, but it truly is involuntary just as patients say it is."
The Associated Press contributed to this report.