Michigan said it had confirmed six cases of fungal meningitis, the seventh state to report people falling ill after receiving the injections, mainly for back pain.

Other states with cases are Tennessee, Virginia, Florida, Maryland, North Carolina and Indiana.

The U.S. Centers for Disease Control reported 47 cases of meningitis on Friday, while Michigan reported an additional two cases and North Carolina one not included in the CDC count. That brought the national total to 50, compared with 35 on Thursday.

Tennessee accounts for most of those, and state officials said on Friday the number there had risen to 29 cases, up four from Thursday. While there were no more deaths reported on Friday, Tennessee officials said on Thursday there were more patients in critical condition in intensive care.

Three of the deaths so far have been in Tennessee, where the outbreak began, and one each in Virginia and Maryland.

Vials of steroids linked to the outbreak were shipped to 76 facilities in 23 states and could have been used to inject thousands of patients, authorities have said.

"All patients who may have received these medications need to be tracked down immediately," Dr. Benjamin Park, a medical officer in the CDC Mycotic Diseases Branch, said on Friday in a statement. "It is possible that if patients with infection are identified soon and put on appropriate antifungal therapy, lives may be saved."

While fungal meningitis is rare and life-threatening, it is not spread by person-to-person contact.

The infected patients have shown a variety of symptoms from one to four weeks after their injections, including fever, a new or worsening headache, nausea and neurological problems that would be consistent with deep brain stroke, the CDC said.

All the cases have so far been traced to three lots of the steroid prepared at New England Compounding Center Inc in Framingham, Massachusetts. The company said it had suspended its operations while the investigation proceeds.

RATE OF INFECTION NOT YET DETERMINED

The Massachusetts Health Department said there were 17,676 vials of medication in each of the three lots of methylprednisolone acetate sent out July through September and have a shelf life of 180 days.

Dr. Anders Cohen, chief of neurosurgery and spine surgery at the Brooklyn Hospital Center in New York, said patients with back pain should wait to have steroid injections until the CDC confirms all the tainted lots are off the market.

"In the meantime, they can ask their physicians about other alternatives such as oral pain medications," Cohen said.

The CDC said it had not yet determined the rate of infection among patients who received the potentially tainted steroid. The rate of infection is important because it would help pinpoint the scope of the potential outbreak.

In addition to Tennessee, Michigan and North Carolina, six cases have been reported in Virginia, two in Florida, two in Maryland, and three in Indiana, the CDC said.

The steroid was sent to 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 said.

Each state could have hundreds of patients or more who were exposed through injections.

(Reporting by Tim Ghianni; Writing by David Bailey; Editing by Greg McCune and Peter Cooney)

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