WASHINGTON (AP) — The black mold creeping into the spines of hundreds of people who got tainted shots for back pain marks uncharted medical territory.

Never before has this particular fungus been found to cause meningitis. It's incredibly hard to diagnose, and to kill — requiring at least three months of a treatment that can cause hallucinations. There's no good way to predict survival, or when it's safe to stop treating, or exactly how to monitor those who fear the fungus may be festering silently in their bodies.

"I don't think there is a precedent for this kind of thing," said Dr. Arjun Srinivasan of the Centers for Disease Control and Prevention. Health officials and doctors have tracked down most of the 14,000 people potentially at risk for fungal meningitis, blamed for the deaths of 24 people and sickening more than 300.