NEW YORK — Health providers are scrambling to notify patients in nearly two dozen states that the routine steroid injections they received for back pain in recent months may have been contaminated with a deadly fungal meningitis.

It became apparent Thursday that hundreds, and perhaps thousands, of people who got the shots between July and September could be at risk after officials revealed that a tainted steroid suspected to have caused a meningitis outbreak in the South had made its way to 75 clinics in 23 states.

The Food and Drug Administration urged physicians not to use any products at all from the Massachusetts pharmacy that supplied the preservative-free methylprednisolone acetate.

So far, 35 people in six states — Tennessee, Virginia, Maryland, Florida, North Carolina and Indiana — have contracted fungal meningitis, and five of them have died, according to the Centers for Disease Control and Prevention. All had received steroid shots for back pain, a highly common treatment.

It is not clear how many patients received tainted injections, or even whether everyone who got one will get sick.

The time from infection to onset of symptoms is anywhere from a few days to a month, so the number of people stricken could rise.

The pharmacy involved, the New England Compounding Center of Framingham, Mass., has recalled three lots consisting of a total of 17,676 single-dose vials of the steroid, preservative-free methylprednisolone acetate, Massachusetts health officials said.

Investigators this week found contamination in a sealed vial of the steroid at the company, FDA officials said. Tests are under way to determine if it is the same fungus blamed in the outbreak.

Several hundred of the vials, maybe more, have been returned unused, but many others were used.

At one clinic in Evansville, Ind., more than 500 patients received shots from the suspect lots, officials said. At two clinics in Tennessee, more than 900 patients — perhaps many more — did.

The company has shut down operations and said it is working with regulators to identify the source of the infection.

“Out of an abundance of caution, we advise all health care practitioners not to use any product” from the company, said Ilisa Bernstein, director of compliance for the FDA’s Center for Drug Evaluation and Research.