Bacterial meningitis is the most serious type of meningitis. It is a severe, life-threatening condition that can often lead to long-term adverse health consequences. There are four main causes of acute bacterial meningitis:

• Neisseria meningitidis (meningococcus)
• Streptococcus pneumoniae (pneumococcus)
• Haemophilus influenzae
• Streptococcus agalactiae (group B streptococcus).

These bacteria are responsible for more than half of the deaths from meningitis globally and can cause other severe diseases like sepsis and pneumonia.

Additional important causes of meningitis worldwide include other bacteria species (e.g. Mycobacterium tuberculosis, non-typhoidal Salmonella spp., Listeria monocytogenes), viruses (e.g. enteroviruses, herpesviruses and arboviruses), fungi (e.g. Cryptococcus spp.), and parasites (e.g. some species of amoebae).