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 clinics in 23 states.

The Food and Drug Administration urged physicians not to use any products from the Massachusetts pharmacy that supplied the steroid.

The Centers for Disease Control and Prevention says that so far, 35 people in six states have contracted fungal meningitis and five of them have died.