So what's really causing this mystery illness that's caused more than a dozen Genesee County teens to exhibit unexplained symptoms?

Some say it's something in the environment, others say it's a bacterial infection, or, as originally diagnosed, something more psychological. Experts say right now solving this mystery is a process of elimination. Casey Bortnick reports.

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Could it be a case of extreme anxiety – a physical response to emotional trauma?

"It should be the diagnosis of last resort,” said Dr. R P Singh.

Singh is a board certified psychiatrist. He says it's possible more than a dozen students in LeRoy are converting stress into physical symptoms, but unlikely.

"As a physician I'd be extra careful,” he said. "Whatever rare possibilities are there should not be unexplored."

Possibilities like a common bacterial infection.

Dr. Michael Pichichero has spent most of professional career studying strep bacteria. He says the antibodies the body produces to fight it can attack a part of the brain that controls voluntary movement. It's called Pediatric Autoimmune Neuropsychiatric Disorders, or PANDAS.

"You can make the diagnosis on the very first case,” Pichichero said.

Pichichero says the strep antibodies appear in a specialized blood test; one he's written about extensively and one the treating physicians in LeRoy should be aware of.

"If somebody has raised the idea of PANDAS or Sydenham's chorea, I'd be fairly certain that blood test has already been done and it was negative,” said Pichichero.

There's one more popular theory: an environmental toxin.

"Like a railroad car or a spill from a truck,” said J. Grant Esler.

Esler is an expert in environmental management and safety. A Kodak retiree, Esler now lectures his students on the topic at RIT.

"The legal system deals in certainties. The scientists deal in probabilities,” Esler said.

Esler says a train derailment in the 1970s certainly introduced an environmental toxin to the area. Under a scientific dose response model, he says it's unlikely any chemicals remained in the environment long enough to poison these students.

"That you'd have a group of people who come up with the same response suddenly on the same day – it's very unlikely that it would be an environmental thing compared to an emotional thing," Esler said.

“We don't want to miss any physiological basis for their difficulties,” said Singh.

Singh says if all other possibilities are eliminated, it's time to revisit the original diagnosis, as unlikely as it may be.

"It's possible, but it's unusual,” Singh said.