CDC/AP Photo

Health officials are urging thousands of back pain patients to be on the lookout for symptoms of fungal meningitis amid an outbreak that has killed at least five people and sickened 42 across seven states.

The outbreak has been linked to spinal steroid injections, a common treatment for back pain. The steroid, called methylprednisolone acetate, was made by the New England Compounding Center, a specialty pharmacy in Framingham, Mass. that has recalled three lots - 17,676 vials - of the drug and shut down operations.

Roughly 75 clinics in 23 states that received the recalled vials have been instructed to notify all affected patients.

See a list of affected clinics

"If patients are concerned, they should contact their physician to find out if they received a medicine from one of these lots," said Dr. Benjamin Park of the U.S. Centers for Disease Control and Prevention, adding that most of the cases occurred in older adults who were healthy aside from back pain.

Meningitis affects the membranous lining of the brain and spinal cord. Early symptoms of fungal meningitis, such as headache, fever, dizziness, nausea and slurred speech, are subtler than those of bacterial meningitis and can take nearly a month to appear. Left untreated, the inflammatory disease can cause permanent neurological damage and death.

"Fungal meningitis in general is rare. But aspergillus meningitis - the kind we're talking about here - is super rare and very serious," said Dr. William Schaffner, president of the National Foundation for Infectious Diseases and chairman of preventive medicine at Vanderbilt University Medical Center in Nashville, Tenn. "There's no such thing as mild aspergillus meningitis."

The disease is diagnosed with a lumbar puncture, which draws cerebrospinal fluid from the spine that can be inspected for signs of the disease. Once detected, it can be treated with high doses of intravenous antifungal medications, possibly for months.

Twenty-nine of the meningitis cases - three of them lethal - have been in Tennessee, where more than 900 residents received the drug since July. Cases have also been reported in Virginia, Michigan, Indiana, Maryland, Florida and North Carolina.

Robert Barry, 71, received an injection from one of the recalled vials about six weeks ago.

"They told me that if I begin to develop headache, nausea or trouble walking - if I believe that Obama won the debate - I should go to the emergency room," said Barry, who lives in Berlin, Md.

Unlike bacterial meningitis, fungal meningitis is not transmitted from person to person. Only people who received the steroid injections are thought to be at risk, but only one in 100 of them have developed signs of the disease.

"At the moment the attack rate appears to be 1 percent or less, but of course more cases are sure to develop," said Schaffner, adding that the level of contamination may have varied from vial to vial. "Some patients also received more than one dose, which would increase their risk."