At least 91 people have been infected with an unusual type of meningitis caused by contaminated steroid injections, federal health officials said Sunday, with seven deaths. The drugs were given starting May 21, much earlier than previously suspected, officials with the Centers for Disease Control and Prevention said.

They are urging anyone who has had an injection for lower back pain to watch for symptoms of meningitis, which include a stiff neck and balance problems.

Cases have been identified in nine states and health officials fear the numbers will rise as doctors check patients for the symptoms. Doctors and patients alike may not know to look for the unusual infection, which can take weeks to develop after an injection.

"Several of these patients have had strokes related to the meningitis," the CDC said in a statement posted on its website. "In several patients, the meningitis was found to be caused by a fungus that is common in the environment but rarely causes meningitis. This form of meningitis is not contagious. The source of the fungus has not yet been identified, and the cause of infections in the other patients is still being assessed."

The drug in question is called methylprednisone and is used mostly to treat older patients for lower back pain.

The contaminated drugs have been traced to a single pharmacy in Massachusetts, the New England Compounding Center. The pharmacy has closed voluntarily and recalled its products, which include steroids, painkillers and dozens of other drugs. At least one sealed vial of drug has been found to have fungus growing in it, the Food and Drug Administration said. The FDA does not regulate pharmacies like the one in Massachusetts but can be called in when contamination is suspected.

Compounding pharmacies usually make drugs to order, and the steroids suspected of causing the infections did not contain preservatives that can keep fungi and bacteria from growing.

The pharmacy sent products to clinics in California, Connecticut, Florida, Georgia, Idaho, Illinois, Indiana, Maryland, Michigan, Minnesota, North Carolina, New Hampshire, New Jersey, Nevada, New York, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia, Texas, and West Virginia, the CDC says.

In this case, the patients appear to have had contaminated drugs injected directly into their spinal fluid. CDC says the clinics do not appear to be to blame. The CDC said it has found fungus, including Aspergillus and Exserohilum, in specimens from nine patients.

Meningitis is an inflammation of the protective membranes covering the brain and spinal cord. Bacteria or viruses are the usual cause, but meningitis can also be caused by fungi and parasites. "In addition to typical meningitis symptoms, like headache, fever, nausea, and stiffness of the neck, people with fungal meningitis may also experience confusion, dizziness, and discomfort from bright lights. Patients might just have one or two of these symptoms," CDC said.

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