Question: My child is due to have cochlear implant surgery soon. I’ve heard cochlear implant recipients have a higher risk of contracting meningitis. What precautions can we take?
Dr Melville da Cruz
Answer: Melville da Cruz – Ear, Nose & Throat Surgeon
Meningitis is a serious infection of the fluids and linings surrounding the brain and spinal cord, caused by a range of viruses or bacteria. The incidence of meningitis following cochlear implantation has been very low.
The report that caused concern
However, there was a concern about the risk of meningitis following a report in the US (1) in Sept 2003 of a cluster of bacterial meningitis cases in cochlear implant recipients.
The report investigated 118 cases of reported meningitis cases in implant recipients from 13 months to 81 years old. 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 Streptococcus pneumonia. These cases suggested meningitis was more prevalent in implantees, however, these cases were over a 20 year period and approximately 60,000 implant surgeries. In the paediatric population, the incidence of implant-associated meningitis was higher than in non-implanted children indicating that cochlear implant surgery was an added risk factor for meningitis.
The real picture & causes
Follow up clinical and laboratory-based investigations suggested multiple factors lead to the ‘at risk’ profile. These risk factors included the presence of inner ear malformations, CSF leak (2) during or after implantation, history of VP shunt (2) (used for treating hydrocephalus) and recurrent otitis media (middle ear infection).
In addition, an electrode with a positioner was used in a high proportion of the cases of meningitis. The positioner involved a small wedge to place the electrode closer to the auditory nerve endings. Withdrawn from the market, subsequent modified electrode designs minimise this risk.
Minimising risk of meningitis
Several strategies minimise the risk of post-implantation meningitis. The adoption of a range of strategies is up to the protocols in various implant clinics, individual surgeons, implant recipients and their families.
Antibiotics are standard during implant surgery and continued for several days after. Similarly, the insertion of a grommet in both the implanted and non-implanted ears is also common. This helps reduce the incidence of recurrent acute otitis media in infection-prone children.
Immunisation against a range of bacteria for all implant recipients is important. Particularly 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 children and adults have access to a range of bacterial vaccines to minimise the chances of infection. Particularly Streptococcus pneumonia, Haemophilus influenza type B (HIB) and meningococcus, from a young age.
Streptococcus pneumonia is the most common bacterium in post-implant meningitis. So, immunisation is strongly recommended for all ages. The immunisation schedule is widely practised (2) and updated as new knowledge and more effective vaccines are available.
Hopefully, these measures will see a further reduction in the already low incidence of bacterial meningitis in cochlear implant recipients over time.
(1) Cochlear implants. Bethesda, Md.: National Institute on Deafness and Other Communication Disorders, 2003. (Accessed 1 July 1 2003, at www.nidcd.nih.gov/health/hearing/coch.asp.)
(2) www.health.gov.au/internet /immunise/publishing.nsf.
A ventriculoperitoneal (VP) shunt relieves pressure from the brain caused by fluid accumulation. VP shunting is a surgical procedure primarily to treat hydrocephalus. Hydrocephalus occurs when excess cerebrospinal fluid (CSF) collects in the brain’s ventricles. CSF cushions your brain and protects it from injury inside your skull.
The fluid acts as a delivery system for nutrients that your brain needs, and also takes away waste products. Normally, CSF flows through these ventricles to the base of the brain. The fluid bathes the brain and spinal cord then is reabsorbed into the blood. When this normal flow is disrupted, the build-up of fluid can create harmful pressure on the brain’s tissues. This can damage the brain. VP shunts surgically placed inside one of the brain’s ventricles diverts fluid away from the brain. This restores the normal flow and absorption of CSF.
This FAQ originally appeared in Hearing HQ Magazine