Cochlear implants carry risk of meningitis, agencies warn

Patients with cochlear implants should be vaccinated against the bacteria that cause bacterial meningitis, warn the UK Medical Devices Agency and the US Food and Drug Administration.

Both organisations have issued a public health warning on the association of meningitis with cochlear implants after 25 cases of the disease, nine of them fatal, were reported in patients who received the implants. The FDA suspects, on the basis of an informal survey of centres that performthe implantations, that the true incidence is greater and that other cases have gone unreported.

The cases, reported in the United States and in Europe, involved patients aged from 21 months to 63 years. The onset of meningitis symptoms from time of implantation ranged from 24 hours to five years. Results from tests of cerebrospinal fluid were available in 11 cases. Pneumococcus was identified as the culprit in seven of those cases and suspected in four cases with unidentified diplococci.

One case of suspected bacterial meningitis after a cochlear implantation has been diagnosed in the United Kingdom and successfully treated. There are 3300 people with such implants in the United Kingdom, so the deputy chief medical officer for England and Wales, Dr Pat Troop, assured patients meningitis was a small risk.

While some cases of meningitis may be due to the cochlear implantation procedure itself, the picture is complicated, because many people who need the procedure are at increased risk of bacterial meningitis because of congenital defects of the inner ear and inherent cerebrospinal fluid leak.The implant itself may be to blame because it is a foreign body and can be a source of infection.

Cochlear implants are sophisticated electrodes that can restore some degree of hearing in people with severe sensorineural deafness. They are inserted into the cochlea of the inner ear where they assume the role of the non-functional or absent sensory hair cells by converting sound vibration into electrical signals picked up by the auditory nerves.

About 60000 patients worldwide with profound sensorineural hearing loss have undergone cochlearimplantation since the procedure was developed in 1978. Two of the three companies that make the implants have reported cases of bacterial meningitis in patients who have had an implant.

Because of the risk, Advanced Bionics, one of the manufacturers, has voluntarily withdrawn one component of its devices, a positioner which may induce a cerebrospinal fluid leak. The positionerhelps position the implant electrode closer to the auditory nerve.

However, the company does not recommend removing the device if already implanted and emphasisesthat the risk of contracting meningitis from the device is less than 1%.

In its notification the FDA recommends that all patients undergoing cochlear implantation should be considered for prophylactic antibiotic treatment before the procedure.