Meningitis

The most common infectious causes of meningitis vary according to an individual host's age, habits and living environment, and health status. In newborns, the most common agents of meningitis are those which are contracted from the newborn's mother, including Group B streptococci (becoming an increasingly common infecting organism in the newborn period), Escherichia coli, and Listeria monocytogenes. Older children are more frequently infected by Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae, while adults are infected by S. pneumoniae and N. meningitidis. N. meningitidis is the only organism that can cause epidemics of meningitis. These have occurred in particular when a child in a crowded day-care situation or a military recruit in a crowded training camp has fallen ill with N. meningitidis meningitis.

Viral causes of meningitis include the herpes simplex viruses, mumps and measles viruses (against which most children are protected due to mass immunization programs), the virus which causes chicken pox, the rabies virus, and a number of viruses which are acquired through the bite of infected mosquitoes. Patients with AIDS (acquired immune deficiency syndrome) are more susceptible to certain infectious causes of meningitis, including by certain fungal agents, as well as by the agent which causes tuberculosis. Patients who have had their spleens removed, or whose spleens are no longer functional (as in the case of patients with sickle cell disease) are more susceptible to certain infections, including those caused by N. meningitidis and S. pneumoniae.