6 causes of bacterial meningitis

Various bacteria can cause bacterial meningitis, the most common being meningococcal and pneumococcal bacteria.

1. Streptococcus pneumoniae

Meningitis caused by Streptococcus pneumoniae (pneumococcus) is called pneumococcal meningitis and is the most common form of meningitis, accounting for about 6,000 cases each year in the United States. 

Pneumococcal meningitis is the most serious variety of bacterial meningitis with a risk of complications, such as hearing loss and brain damage. Fortunately, safe and effective vaccines are available to protect against certain pneumococcal strains. 

Besides meningitis, Streptococcus pneumoniae causes other diseases, including pneumonia, sinus and ear infections, and septicemia (blood poisoning). People who are immunocompromised (such as patients with human immunodeficiency virus, organ transplant and cancer) and children under the age of 2 are particularly at risk.

2. Neisseria meningitidis (meningococcus)

Meningococcus bacteria cause a type of meningitis called meningococcal meningitis, which is another common form of meningitis accounting for about 2,600 cases each year in the United States. 

Meningococcal meningitis is a highly infectious disease, particularly affecting immunocompromised infants and adults. The risk is high in people traveling to places where meningococcal infections are endemic. Military recruits and people residing in dormitories also have a high risk. Due to its high infectivity, close contacts of a person diagnosed with meningococcal meningitis are administered prophylactic (preventive) antibiotics. 

Like pneumococcal meningitis, meningococcal meningitis can cause serious disease, leading to death in about 10%-15% of cases. Affected people have a 10%-15% of developing serious complications such as brain damage.

3. Haemophilus influenzae

Previously one of the most common forms of meningitis (particularly in children under age 5), Haemophilus influenzae meningitis cases have declined due to the widespread use of the Haemophilus influenzae b vaccine in the United States. The disease is particularly seen in immunocompromised individuals, unvaccinated children, and people in child-care settings.

4. Listeria monocytogenes

Meningitis caused by listeria is particularly seen in pregnant women and immunocompromised individuals. The infection generally occurs upon consuming contaminated foods such as raw vegetables, deli meats, hot dogs, and foods made with unpasteurized milk.

5. Escherichia coli (E coli)

Some strains of E coli (such as E coli K1) may cause meningitis particularly in newborns (especially premature and low birth weight babies) and elderly individuals. Newborns typically get the infection through the mother’s birth canal. People with a cerebrospinal fluid shunt (a device to relieve excessive pressure around the brain) are also at risk of getting E coli meningitis.

6. Mycobacterium tuberculosis

Meningitis caused by mycobacterium is called tuberculous meningitis, which is typically seen in people who have or had tuberculosis. The infection is generally seen in developing countries where tuberculosis is common.