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.[2] The incidence in African countries is 10 to 40 per 100,000 persons per year.[2]

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%.[2][3] A decline in pneumococcal disease has also been noted in countries that have introduced the pneumococcal vaccine in people older than 65 years (54%).[4] Nonetheless, pneumococcal meningitis remains highly lethal, with about 1 in 5 cases in adults resulting in death.[4]

Risk factors

Older people are more commonly affected because of impaired or waning immunity.[2] 

Ideal for bacterial transmission. Outbreaks have been reported in US college dormitories and in training camps for military recruits.[1]

Risk of acquiring bacterial meningitis is increased after exposure to infection within the household or close contact with a patient who has meningitis.[1]

Ask about a source of infection such as otitis media/sinusitis or contact with a person who has had suspected sepsis.[15]

About 50% of patients with bacterial meningitis have a predisposing condition, including chronic conditions such as diabetes, alcohol misuse, or eculizumab therapy.[15]

One third of patients with predisposing conditions have an immunodeficiency.[16] Bacterial meningitis is primarily caused by Streptococcus pneumoniae, but Salmonella meningitis is also possible in this population.[17][18]

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.[19]

Asplenia or hyposplenia increases the risk of overwhelming bacterial infections with encapsulated bacteria, particularly S pneumoniae and Haemophilus influenzae.[19]

HIV infection makes people susceptible to bacterial meningitis, particularly if they develop AIDS. Patients with leukaemia and lymphoma are also susceptible to bacterial meningitis.[17]

Congenital or acquired cranial anatomical defects may increase risk.[1] 

Suspect anatomical defects in cases of recurrent meningitis.[17]

Recipients of cochlear implants are at higher risk of bacterial meningitis than the general population.[1]

Patients are more likely to get meningitis due to impaired splenic function and impaired complement cascade among other mechanisms.[20]

Infections such as sinusitis, pneumonia, mastoiditis, and otitis media increase the risk of meningitis.[1]

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