Brain & Nervous System Health Center

Understanding Meningitis -- the Basics

What Is Meningitis?

Meningitis is inflammation of the delicate membranes -- called meninges (men-in'-jeez) -- that cover the brain and spinal cord. Meningitis is usually caused by infection from viruses or bacteria.

Bacterial meningitis can be serious and deadly. Viral meningitis tends to be less severe, and most people recover completely. Fungal meningitis is a rare form and generally occurs in people with weakened immune systems. Meningitis can also be due to non-infectious causes, such as cancer or medications.

What Causes Meningitis?

Meningitis is almost always caused by a bacterial or viral infection that began elsewhere in the body, such as in the ears, sinuses, or upper respiratory tract. Less common causes of meningitis include fungal infection, autoimmune disorders, and medications.

Bacterial Meningitis

Bacterial meningitis is an extremely serious illness that requires immediate medical care. If not treated quickly, it can lead to death within hours -- or lead to permanent damage to the brain and other parts of the body.

Bacterial meningitis is caused by any one of several bacteria. Neisseria meningitidis or "meningococcus" is common in children and young adults, and Streptococcuspneumoniae or "pneumococcus" is another common cause in children and adults. Haemophilus influenzae type b (Hib) was a common cause of meningitis in infants and young children until the Hib vaccine was introduced for infants. Neisseria meningitidis and Streptococcus pneumoniae account for most of the bacterial meningitis cases in the U.S. Vaccines are available for both Neisseria meningitidis and Streptococcus pneumoniae. They're recommended for all children and adults at special risk. 

The bacteria can spread from person to person through coughing and sneezing. If you are around someone who has bacterial meningitis, contact your doctor to ask what steps you need to take to avoid infection.

In many instances, bacterial meningitis develops when bacteria get into the bloodstream from the sinuses, ears, or other part of the upper respiratory tract. The bacteria then travel through the bloodstream to the brain.

Viral Meningitis

Viral meningitis is more common than the bacterial form and generally -- but not always -- less serious. It can be triggered by a number of viruses, including several that can cause diarrhea.

People with viral meningitis are much less likely to have permanent brain damage after the infection resolves. Most will recover completely.

Fungal Meningitis

Fungal meningitis is much less common than the other two infectious forms. Fungus-related meningitis is rare in healthy people. However, someone who has an impaired immune system is more likely to become infected with this form of meningitis.