There are four main causes of acute bacterial meningitis:
  • Neisseria Meningitidis (Meningococcus)
  • Streptococcus Pneumoniae (Pneumococcus)
  • Haemophilus Influenzae
  • Streptococcus Sgalactiae (Group B Streptococcus)

These bacteria are responsible for more than half of the deaths from meningitis globally and they cause other severe diseases like sepsis and pneumonia.
other bacteria species (e.g. Mycobacterium tuberculosis, non-typhoidal Salmonella spp, Listeria monocytogenes), viruses (e.g. enteroviruses, herpesviruses an arboviruses), fungi (e.g. Cyptococcus spp.), and parasites (e.g. some species of amoebae).

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Transmission

The bacteria that cause meningitis are transmitted from person-to-person through droplets of respiratory or throat secretions from carriers. Close and prolonged contact – such as kissing, sneezing or coughing on someone, or living in close quarters with an infected person, facilitates the spread of the disease. The average incubation period is 4 days but can range between 2 and 10 days.

Neisseria meningitidis only infects humans. The bacteria can be carried in the throat and can sometimes overwhelm the body's defences allowing infection to spread through the bloodstream to the brain. A significant proportion of the population (between 5 and 10%) carries Neisseria meningitidis in their throat at any given time.