NASHVILLE, Tenn. (AP) — An outbreak of a rare form of meningitis is likely to grow after sickening 26 people in five states, including four who died, health officials warned.

All received steroid injections, mostly for back pain, a fairly typical treatment.

The drug was made by a specialty pharmacy in Massachusetts that issued a recall last week and has shut down operations.

The type of meningitis involved is not contagious like the more common forms. This type is caused by a fungus often found in leaf mold and which health officials suspect may have been in the steroid.

Eighteen of the cases are in Tennessee, where a Nashville clinic received the largest shipment of the steroid. Investigators, though, say they are still trying to confirm the source of the infection.

Three cases have been reported in Virginia, two in Maryland, two in Florida and one in North Carolina. Two of the deaths were in Tennessee, and Virginia and Maryland had one each, said officials at the Centers for Disease Control and Prevention.

More new cases are almost certain to appear in the coming days, said Tennessee Department of Health Commissioner John Dreyzehner.

Five new cases were confirmed over the past 24 hours, he said Wednesday, calling the situation a “rapidly evolving outbreak.”

Meningitis is an inflammation of the lining of the brain and spinal cord. Symptoms include severe and worsening headache, nausea, dizziness and fever. Some of the patients also experienced slurred speech, and difficulty walking and urinating, Tennessee health officials said.