Understanding Meningitis - the Basics

What Is Meningitis?

Meningitis is a relatively rare infection that affects the delicate membranes -- called meninges (men-in'-jeez) -- that cover the brain and spinal cord.   Bacterial meningitis can be contagious among people in close contact -- such as in classrooms and university dorms.

Viral meningitis tends to be less severe, and most people recover completely.  Fungal meningitis is a rare form and generally occurs only in people with weakened immune systems.

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

The bacterial form of 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 brain damage.

Bacterial meningitis is caused by any one of several bacteria. . Neisseria meningitidis or "meningococcus" is common in young adults, and Streptococcus pneumoniae or "pneumococcus" is the most common form in adults.  Haemophilus influenzae type b (Hib) was a common form in infants until theHib vaccine was introduced for infants. Neisseria meningitidis and Streptococcus pneumoniae account for about most of the bacterial meningitis cases in the United States. Vaccines are available for both Neisseria meningitidis and Streptococcus pneumoniae.

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 if you need to take steps so you don't become infected.

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 such as a person with AIDS is more likely to become infected with this form of meningitis.