Aetiology

The routine use of Haemophilus influenzae type b (Hib) and conjugate pneumococcal vaccines in the UK and other developed countries has markedly reduced the overall incidence of bacterial meningitis.[2][4][5][6][7] However, because of limited economic resources and poor living conditions, many developing countries continue to have high rates of disease.

Streptococcus pneumoniae is the most common cause of bacterial meningitis in many countries worldwide.[4] However, after the introduction of the 13-valent pneumococcal conjugate vaccine (PCV13), the incidence of invasive pneumococcal disease in England and Wales decreased by 32%.[8] S pneumoniae can cause systemic infection at any age.[3]

Neisseria meningitidis serogroup B is the predominant cause of meningococcal meningitis in Europe, the US, and the Western Pacific. Meningococcal serogroups C and W are most common in most of Africa and Latin America. Serogroup Y cases mostly occur in Nordic countries.[9]

Listeria monocytogenes is a common cause of bacterial meningitis in patients using immunosuppressive drugs, people who misuse alcohol, and patients with diabetes mellitus.[10][11]

Zoonotic causes of bacterial meningitis are rare, but important to consider when there is a history of exposure to animals. Streptococcus suis, most prevalent in Southeast Asia, is associated with raw pork meat and pig farming. Other zoonotic pathogens include Capnocytophaga canimorsus (associated with dogs), Campylobacter fetus (cattle), and Streptococcus equi (horses).[12][13][14]

For information on meningococcal disease caused by N meningitidis (not covered here) see  Meningococcal disease.

Pathophysiology

Bacteria reach the central nervous system either by haematogenous spread (the most common route) or by direct extension from a contiguous site. The bacteria multiply quickly once they have entered the subarachnoid space. Bacterial components in the cerebrospinal fluid induce the production of various inflammatory mediators, which in turn enhance the influx of leukocytes into the cerebrospinal fluid.[15] The inflammatory cascade leads to cerebral oedema and increased intracranial pressure, which contribute to neurological damage and even death.[Figure caption and citation for the preceding image starts]: Image provided by the US Centers for Disease Control and Prevention Public Health Image Library [Citation ends].

Classification

Common types of bacterial meningitis

Pneumococcal meningitis

  • Caused by Streptococcus pneumoniae

Meningococcal meningitis (not covered here)

  • Caused by Neisseria meningitidis

Hib meningitis

  • Caused by Haemophilus influenzae type b

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