Meningitis Center

Meningitis Causes and Risk Factors

Types of meningitis

Bacterial meningitis - These infections are the most dangerous variety of meningitis, and can be the result of several different types of bacteria.  Bacterial meningitis occurs when bacteria migrates to the brain and spinal cord from the blood stream, or when bacteria directly attacks the meninges from an ear or sinus infection.  Different strains of bacteria tend to attack people in different segments of the population.  They include:

Haemophilus influenza (haemophilus) type b - This strain was the most common cause of bacterial meningitis before the 1990s, when new vaccines became available.  Type b bacterial meningitis usually occurs after a case of ear infection, upper respiratory infection, or sinusitis.

Listeria monocytogenes (listeria) - This strain of bacteria is practically everywhere:  food (cheese, meat, etc.), soil, and on animals.  People who work with farm animals are especially at risk.  However, most healthy people do not contact it.  New born babies, older adults, and pregnant women tend to catch this strain the most.  Listeria can be transmitted from mother to fetus, resulting in a stillborn death or the baby dying after birth.

Neisseria meningitidis (meningococcus) - This strain of bacteria usually occurs when a person has an upper respiratory infection when the infection enters the blood stream.  Because meningococcus is especially contagious, epidemics are possible in areas where many people live together (college dormitories; daycares; military housing; etc).

Streptococcus pneumoniae (pneumococcus) - This strain affects mostly babies and young children, and can lead to pneumonia and ear/sinus infections.  

Chronic meningitis - During these cases of meningitis, meningitis takes four or more weeks to occur, in contrast to acute meningitis, which occurs very quickly.  Chronic meningitis is relatively uncommon. 

Fungal meningitis - Fungal meningitis is also uncommon, but that may affect people with weak immune systems (for example, people with AIDS; persons taking immunosuppressant drugs; etc.).

Viral Meningitis  - Each year in the US, more cases of meningitis occur from viral infections than bacterial infections. These infections are usually significantly milder than bacterial infections, and may be treated by allowing the body's immune system to do its own job.  Children under the age of 5 account for most cases of viral meningitis.     

If meningitis is potentially contagious, and can sometimes be life-threatening, how do you determine if you have symptoms of meningitis?  Continue reading here for more information on meningitis. We'll cover the common symptoms of meningitis in our Meningitis Symptoms section that follows.

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