Up to one-third of pneumococcal meningitis survivors are disabled by hearing loss. Often, clinicians are unaware of the problem because patients are not fully conscious. Additionally, hearing loss may continue to develop in the weeks after diagnosis. Few studies have identified clinical risk factors for its development, and until recently, only advanced age, female gender, a low level of consciousness, infection with S. pneumoniae
, and elevated clinical markers of inflammation in cerebrospinal fluid (CSF) and serum had been suggested as causing or contributing to hearing loss. Researchers have suspected that pneumococcal serotype may also be associated with an increased risk of hearing loss.
identified a diagnosis of otitis at the time of hospital as the main risk factor for hearing loss. Unable to corrolate disease severity or levels of CSF inflammation with otitis, they suggest that perilympathic inflammation that follows otitis may cause hearing loss and especially high-frequency hearing impairment. During an episode of otitis, toxic bacterial products and inflammatory mediators may cause perilymphatic inflammation and permanent cochlear damage.
Clinicians have used adjunctive anti-inflammatory agents, including steroids, in attempts to reduce morbidity and mortality associated with meningitis. Dexamethasone improves overall outcomes and mortality. It did not appear to lower the risk of hearing loss in this study, but it did seem to lessen the magnitude of the loss.
This study and several other identified pneumococcal serotype 3 as being associated with the highest risk of hearing loss. Serotype 23F seems to have the lowest risk. Infection with both these serotypes is vaccine-preventable.
Health care providers should assess hearing frequently, and refer affected patients for otolaryngological evaluation and coclear implantation at the earliest possible time.