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Most cases of meningitis are due to a bacterial or viral infection. The infection may be primary – starting in the meninges, or secondary – spreading from an infection in another part of the body. Viral meningitis is the most common form of meningitis in Australia. It is usually mild to moderate in severity and self-limited. Viral meningitis is frequently caused by an enterovirus or herpes virus but may also be caused by arboviruses (see Encephalitis above).

Bacterial meningitis is a medical emergency. Cases can arise suddenly, with symptoms worsening within hours to a couple of days. Rapid identification and treatment is crucial. Untreated bacterial meningitis is usually fatal. While this condition can be caused by many different types (species) of bacteria, the most common causes are:

  • Streptococcus pneumoniae – called pneumococcal meningitis. Infants under 2 years old and those with compromised immune systems are at greatest risk for it. A pneumococcal vaccine is now given as part of the routine immunisation programme in Australia. It protects against some forms of pneumococcal meningitis
  • Neisseria meningitidis – called meningococcal meningitis. More commonly seen in college students, infants, children, international travellers, and the immune-compromised. It is the leading cause of bacterial meningitis in children and young adults and is highly contagious. There are 13 known serogroups, designated by letters of the alphabet, of which A, B, C, W135 and Y most commonly cause disease. Since the introduction of a meningococcal vaccine, many cases have been prevented however not all strains are covered by the currently available vaccines. 
  • Haemophilus influenzae type b – once the most common cause of bacterial meningitis, its incidence has decreased because of widespread vaccination of children.
  • Group B streptococcus, Escherichia coli, and Listeria monocytogenes are the most common causes of meningitis in the neonate (babies less six weeks old) and may be passed from the mother to her baby.

Chronic meningitis is meningitis that lasts for more than 4 weeks. It may be caused by bacteria such as Mycobacterium tuberculosis, which causes tuberculosis, by Treponema pallidum, which causes syphilis, and by fungi. Fungal meningitis is most commonly seen in immune-compromised patients, such as those with HIV/AIDS, but may affect anyone. The most common causes are Cryptococcus neoformans and Cryptococcus gattii (cryptococcal meningitis), which are inhaled from the environment. Other uncommon fungal causes include Candida species, Aspergillus species and Histoplasma capsulatum

Amoebic meningitis is rare and is usually lethal. It is caused by the free-living amoeba, Naegleria fowleri, a single-cell parasite, which can be found in warm water lakes and rivers. Eosinophilic meningitis may be caused by a parasitic infection such as Angiostrongylus cantonensis, Gnathosoma species and Baylisacarensis species. Cases have been reported in Australia as a result of eating garden snails and slugs.

Last Review Date: December 4, 2020