At the exact moment the stone gave him CTS, Jay was at the mall, leaving the bookstore. He wasn't with anyone, but he was surrounded by those who could potentially be afflicted.
Syndromes, by their very nature, have no discovered cause. They are merely a collection of symptoms that have been proven to have a connection with each other.
No one knew how one contracted Characteristic Transformation Syndrome, but those familiar with it knew what the symptoms were, and what it did to others. There was no cure, but fortunately, the majority of the patients recover, although the side effects can take months or even years to deal with.
There were so few cases, even in the reality Jon's wish created, that few people had even heard of it.
Jay walked toward the exit quietly, when he suddenly heard a familiar set of voices...voices he recognized from school.