The incidence of bacterial meningitis in Western countries is 0.7 to 0.9 per 100,000 persons per year and has decreased by 3% to 4% in the past 10 to 20 years. The incidence in African countries is 10 to 40 per 100,000 persons per year.
The epidemiology of bacterial meningitis has changed due to widespread immunisation programmes with new vaccines. For example, in countries that use universal immunisation with Haemophilus influenzae type b (Hib) vaccine, the incidence of bacterial meningitis caused by this pathogen has declined by 95% to 99%. A decline in pneumococcal disease has also been noted in countries that have introduced the pneumococcal vaccine in people older than 65 years (54%). Nonetheless, pneumococcal meningitis remains highly lethal, with about 1 in 5 cases in adults resulting in death.
Older people are more commonly affected because of impaired or waning immunity.
Ideal for bacterial transmission. Outbreaks have been reported in US college dormitories and in training camps for military recruits.
About 50% of patients with bacterial meningitis have a predisposing condition, including chronic conditions such as diabetes, alcohol misuse, or eculizumab therapy.
One third of patients with predisposing conditions have an immunodeficiency. Bacterial meningitis is primarily caused by Streptococcus pneumoniae, but Salmonella meningitis is also possible in this population.
Congenital immunodeficiencies, such as complement deficiencies, X-linked agammaglobulinaemia, immunoglobulin G subclass deficiency, or interleukin 1 receptor-associated kinase 4 deficiency, have been associated with bacterial meningitis.
Asplenia or hyposplenia increases the risk of overwhelming bacterial infections with encapsulated bacteria, particularly S pneumoniae and Haemophilus influenzae.
HIV infection makes people susceptible to bacterial meningitis, particularly if they develop AIDS. Patients with leukaemia and lymphoma are also susceptible to bacterial meningitis.
Recipients of cochlear implants are at higher risk of bacterial meningitis than the general population.
Patients are more likely to get meningitis due to impaired splenic function and impaired complement cascade among other mechanisms.
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