The most common causes of meningitis are viral infections that usually resolve without treatment. However, bacterial infections of the meninges are extremely serious illnesses, and may result in death or brain damage even if treated. Meningitis is also caused by fungi, chemical irritation or drug allergies, and tumors.

Types include:

• meningitis - cryptococcal
• syphilitic aseptic meningitis
• meningitis - H. influenza
• meningitis - meningococcal
• meningitis - pneumococcal
• meningitis - staphylococcal
• meningitis - tuberculous
• aseptic meningitis
• meningitis gram negative
• carcinomatous meningitis (meningitis due to cancer)

Acute bacterial meningitis is a true medical emergency, and requires immediate hospital-based treatment. Bacterial strains that cause meningitis include Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis (meningococcus), Listeria monocytogenes, and many other types of bacteria. In the U.S. about 17,500 cases of bacterial meningitis occur each year.

Viral meningitis is milder and occurs more often than bacterial meningitis. It usually develops in the late summer and early fall, often affects children and adults under 30. Seventy percent of the infections occur in children under the age of 5. Most viral meningitis is associated with enteroviruses, which are viruses that commonly cause stomach flu.

However, many other types of viruses can also cause meningitis; for example, viral meningitis may occur as a complication in people with genital herpes. Recently, West Nile virus spread by mosquito bites has become a cause of viral meningitis in most of the U.S. In addition to causing viral meningitis, West Nile virus can cause encephalitis in some patients and a polio-like syndrome in others.

• fever and chills
• severe headache
• nausea and vomiting
• stiff neck ("meningismus")
• sensitivity to light (photophobia)
• mental status changes

• decreased consciousness
• rapid breathing
• agitation
• opisthotonos (severe neck stiffness, ultimately resulting in a characteristic arched posture-seen in infants or small children)
• "bulging fontanelles" may be seen in infants
• poor feeding or irritability in children

Meningitis is an important cause of fever in newborn children. For this reason, a lumbar puncture is often done on newborns who have a fever of uncertain origin.

• Lumbar puncture with CSF glucose measurement and CSF cell count.
• Gram-stain and culture of CSF (cerebral spinal fluid).
• Chest X-ray to look for other sites of infection.
• Head CT scan looking for hydrocephalus, abscess or deep swelling.

• hearing loss / deafness
• brain damage
• loss of vision
• hydrocephalus

• Haemophilus vaccine (HiB vaccine) in children will help prevent one type of meningitis.
• The Pneumococcal Conjugate Vaccine is now a routine childhood immunization and is very effective at preventing pneumococcal meningitis
• It is highly recommended that household contacts and individuals with close contact with individuals with meningococcal meningitis receive preventative antibiotics to avoid becoming infected themselves.
• Some communities conduct vaccination campaigns following an outbreak of meningococcal meningitis. Military recruits are routinely vaccinated against this form of meningitis because of its high rate of occurrence.
• The American Academy of Pediatrics and the American College Health Association encourage college students (particularly freshmen living in dormitories) to consider being vaccinated with the meningococcal vaccine.