Most cases of meningitis stem from viruses and bacteria that have entered the body, notes WebMD. For the most part, these germs remain in the gastrointestinal tract or the throat and nose, where they're less likely to cause illness. When they spread to the meninges, the resulting inflammation is meningitis.
The meninges are the tissues surrounding the spinal cord and brain. The most frequently occurring form of meningitis is viral, and it also causes the least concern. The cause is enteroviruses that dwell in the intestines but spread through water, food or contaminated surfaces. Viral meningitis is most common in young children and babies, according to WebMD.
Bacterial meningitis is far more serious than viral meningitis. Transmission occurs when infected people pass mucus or saliva to others. One of the most common bacterial sources is Neisseria meningitidis, which dwells in the throat without causing illness. However, it's possible to pass those to other people who develop bacterial meningitis. The other most common source is Streptococcus pneumoniae, a bacterial strain that causes pneumonia and sinus and ear infections in addition to meningitis, as stated by WebMD.
Some other bacteria that cause meningitis are Group B streptococci, most common in newborns; Listeria monocytogenes, which strikes older adults and newborns most frequently; and Haemophilus influenzae, which hits both children and adults, generally after an upper respiratory infection, states WebMD.