Cause

Most meningitis is caused by bacteria and viruses that often live in our bodies. Usually these germs stay in the intestines or in the nose and throat, where they may or may not make us sick. But if they spread to the tissues (meninges) that surround the brain and spinal cord, they cause inflammation. This inflammation is called meningitis.

The germs that can lead to meningitis are contagious, which means they can be passed easily from one person to another.

Viral meningitis

Viral meningitis is the most common and the least dangerous. It's caused by viruses, most often enteroviruses that live in the intestines. These germs can be spread through food, water, or contaminated objects. Meningitis caused by enteroviruses occurs most often in babies and young children.

Bacterial meningitis

Bacterial meningitis is caused by bacteria. It is a very serious illness. These germs are usually passed from one person to another through infected saliva or mucus. Most people who get bacterial meningitis get it from one of two types of bacteria:¹

• Streptococcus pneumoniae. This is a common germ that causes a number of illnesses besides meningitis, such as ear and sinus infections and pneumonia.
• Neisseria meningitidis. This is bacteria you can have in your throat without getting sick. But you can pass it to others, who may then get seriously ill with meningitis.

In the United States, bacterial meningitis mainly affects adults.²

Two other bacteria that sometimes cause meningitis are:

• Group B streptococci. This type of meningitis occurs most often in newborns, who can become infected during or after birth.
• Listeria monocytogenes. This type of meningitis occurs most often in newborns and in older adults.

The Centers for Disease Control and Prevention (CDC) recommends screening for group B streptococci in all pregnant women at 35 to 37 weeks. Women who have the bacteria are given antibiotics during labor in order to prevent infection in their newborns, and this practice has worked well.³

In rare cases, other bacteria cause meningitis, usually in people with long-term medical conditions. Meningitis also can be caused by other organisms and conditions. It can be a complication of an illness, an injury (particularly to the skull or face), or brain surgery.

How meningitis is spread

Germs that cause meningitis can be spread:

• During birth. A mother can pass germs that cause meningitis to her baby even if the mother doesn't have symptoms. Delivering a baby by cesarean section rather than through the birth canal doesn't always protect the baby from getting the infection. Both bacteria and viruses can be transmitted this way.
• Through stool. Stool could have enteroviruses or certain types of bacteria in it. Washing hands on a regular basis can help prevent you and your children from getting infected this way. More children than adults get meningitis this way.
• Through coughing and sneezing. Infected people can pass certain bacteria that are normally found in saliva or mucus in their noses and throats.
• Through kissing, sexual contact, or contact with infected blood. The human immunodeficiency virus (HIV) also can cause meningitis and can be passed from an infected person to another person through blood or sexual contact but not through kissing.
• From rodents and insects (rare). For example, the St. Louis encephalitis and West Nile viruses are spread through dust and food contaminated by the urine of infected mice, hamsters, and rats.