The known number of people with fungal meningitis in a multistate outbreak that has already killed seven rose to 91 on Sunday from 64 on Saturday, according to data provided by the U.S. Centers for Disease Control and Prevention. Wikipedia

A rare meningitis outbreak has reportedly sickened 26 people in five states who received steroid injections mostly for back pain, health officials said Wednesday. Four people have died, with more cases expected to pop up, according to the Associated Press.

Reports indicate that 18 of the 26 cases are in Tennessee where a Nashville clinic received the largest shipment of the steroid suspected in the outbreak.

While the drug was apparently made by a specialty pharmacy in Massachusetts that issued a recall last week, investigators tell the AP that they are still trying to confirm the source of the infections.

Furthermore, three of the 26 cases have been reported in Virginia, two in Maryland, two in Florida and one in North Carolina. Two of the deaths were in Tennessee with Virginia and Maryland each having one as well, according to the Centers for Disease Control and Prevention.

Tennessee Department of Health Commissioner John Dreyzehner suggested to reporters that more new cases are almost certain to appear in the coming days. An additional five new cases were confirmed over the past 24 hours, he said Wednesday, calling the situation a "rapidly evolving outbreak."

Meningitis is caused by the inflammation of meninges, which are protective membranes covering the brain and spinal cord.

Experts say the type of fungal meningitis officials are currently dealing with is caused by a common fungus often found in leaf mold. While it doesn’t normal cause disease in healthy people, it is also not contagious like the more common viral and bacterial meningitis.

Symptoms of the infection include worsening and severe headache, nausea, dizziness and fever. Some of the patients in Tennessee also experienced slurred speech and difficulty walking and urinating, Tennessee health officials told reporters.

"Some are doing well and improving. Some are very ill — very, very seriously ill and may die," Dr. David Reagan, a Tennessee health official said of the state's patients.

Officials are reportedly in the process of contacting the more than 900 people who received the steroid at three clinics in Tennessee in the past three months.

The steroid, which is being used for back pain, often given together with an anesthetic, is the primary suspect behind the outbreak. Investigators have been looking into the antiseptic and anesthetic used during the injections.

The Food and Drug Administration identified the maker of the steroid as New England Compounding Center, a specialty pharmacy in Framingham, Mass. Last week, the company issued a recall of three lots of the steroid — methylprednisolone acetate. In a statement, the company said it had voluntarily suspended operations and was working with regulators to identify the source of the infection.

AP reports that the outbreak was discovered about two weeks ago when Vanderbilt University's Dr. April Pettit was treating a patient who was not doing well for reasons doctors did not understand.

According to the chair of Vanderbilt's Department of Preventive Medicine, Dr. William Schaffner, who is cited the AP, Pettit began asking questions and learned the patient recently had steroid injections in his spine when the laboratory found the fungus in the patient's spinal fluid.

"When it became clear that the infection control practices at the clinic were up to par, the steroid medication became implicated," Schaffner said.

Fungal meningitis is treated with high-dose antifungal medications, usually given intravenously in a hospital.

Seventeen of the Tennessee cases were treated at the Saint Thomas Outpatient Neurosurgery Center in Nashville, according to reports. It had 2,000 vials of the suspect lots, the largest number. That clinic voluntarily closed last month to deal with the investigation.