None of the fungal meningitis cases involving tainted steroids from New England Compounding have taken longer than six weeks, from the time of injection, to diagnose. So, state and federal officials might have breathed a sigh of relief on Wednesday, which marked six weeks from the day drugs produced at the Framingham pharmacy were recalled and public health officials began collecting products leftover in physician’s offices.

But they didn’t. Fungal meningitis cases like those resulting from the steroid -- as of Friday there were at least 428, including 32 deaths -- are rare, and public health officials are learning as they go.