Bacterial Meningitis

Bacterial meningitis is a medical emergency that is common in many areas of the tropics. The epidemiology varies with geographical and climatic conditions, with age, with rate of HIV infection and other causes of immunosuppression, and with the availability of vaccines. The epidemiology has substantially changed in the past 25 years after the introduction of vaccines against Haemophilus influenzae type B, Streptococcus pneumoniae, and Neisseria meningitidis, although only recently these vaccinations have reached populations in research poor settings, where the incidence is highest. Currently, two pathogens cause most cases outside the neonatal period: Streptococcus pneumoniae and Neisseria meningitidis. Neonatal meningitis may also be caused by these organisms but other bacteria such as Escherichia coli, Streptococcus agalactiae (Group B streptococcus), and Klebsiella pneumoniae tend to predominate. The relative importance of H. influenzae, pneumococci, and meningococci outside the neonatal period varies according to country; for example, in humid low-lying regions S. pneumoniae and H. influenzae predominate, whereas in dryer regions, for example the meningitis belt of sub-Saharan Africa, the meningococcus causes vast spreading epidemics. Bacterial meningitis has a high mortality and carries a high risk of neurological sequelae.