Meningitis is a serious infection of the fluids and linings surrounding the brain and spinal cord. It can be caused by a range of viruses or bacteria. Although the incidence of meningitis following cochlear implantation has been very low, there was an increased concern of the risk of meningitis by implantees, their families and doctors following a report in the US (Sept 2003) of a cluster of bacterial meningitis cases in cochlear implant recipients. The report investigated 118 meningitis cases in implant recipients. Both adults and children recipients were affected with the age range of 13 months to 81 years. The onset of the infection ranged from less than 24 hours following implant surgery to more than 6 years after. The most common infection was due to a particular organism called Streptococcus pneumonia. Although these cases suggested that meningitis was more prevalent in implantees these cases had occurred over a period of 20 years during which around 60,000 implant surgeries had been performed.
In the paediatric population the incidence of implant-associated meningitis was higher than non-implanted children indicating that cochlear implant surgery was an added risk factor for meningitis. Subsequent investigations, both clinical and laboratory based, suggested that there were multiple factors involved in the meningitis cases leading to an ‘at risk’ profile of implant cases where particular actions are taken around the time of surgery to prevent meningitis. These risk factors included the presence of inner ear malformations, CSF leak2 during or after implantation, history of VP shunt2 (used for treating hydrocephalus) and recurrent otitis media (middle ear infection). There was also a particularly high incidence of post-implant meningitis with an electrode designed with a positioner (a small wedge designed to place the electrode closer to the auditory nerve endings), which has since been withdrawn from the market and subsequent electrode designs modified to minimise this risk. Several strategies have been developed to minimise the risk of post-implantation meningitis. Not all strategies have been universally accepted, with the adoption of a range of strategies being left up to the protocols in various implant clinics, individual surgeons, implant recipients and their families.
Antibiotics are universally administered during implant surgery and continued for several days after. Similarly, measures to reduce the incidence of recurrent acute otitis media in infection-prone children by insertion of a grommet in both the implanted and non-implanted ears, is also commonly practiced. Emphasis has been placed on immunisation against a range of bacteria for implant recipients, particularly children, but also adults, those with inner ear malformations, CSF leak at the time of implantation or with VP shunts to optimise their immunisation status. In Australia the national immunisation program ensures that children and adults have access to a range of bacterial vaccines to minimise the chances of infection, particularly Streptococcus pneumonia, Haemophilus influenzae type B (HIB) and menigococcus, from a young age. Immunisation against Streptococcus pneumonia, the most common bacterium involved in post-implant meningitis is strongly recommend for implantees of all ages by most surgeons. The immunisation schedule is widely practiced, and changes made as new knowledge concerning the prevalence of infections in the community and more effective vaccines become available. Hopefully these measures will see a further reduction in the already low incidence of bacterial meningitis in cochlear implant recipients over time.