Meningitis is an inflammation of the membranes that surround the brain and the spinal cord. Meningitis usually is caused by a bacterial or viral infection that invades the cerebral spinal fluid (CSF) and inflames the meninges. Cerebral spinal fluid (CSF) is the fluid within the open spaces of the brain that protects and cushions the brain and spinal cord. The meninges are the thin membranes lining the brain and spinal cord.
A fungus or parasite also may cause meningitis. The severity of a child's symptoms and prognosis depend on the specific organism that is causing the meningitis. Meningitis can occur in infants, children and adults.
Some bacteria and viruses are more common in certain age groups than others, including the following:
- Bacterial meningitis
In newborns and young babies, the most common bacteria include the following:
- Group B streptococcus
- Escherichia coli (or E. coli)
- Listeria monocytogenes
In older babies and children, the most common bacteria include the following:
- Neisseria meningitidis (meningococcal meningitis)
- Streptococcus pneumonia
- Haemophilus influenzae type b
Other bacterial infections that may cause meningitis include the following:
- Tuberculosis (TB)
- Viral meningitis
Viruses that can cause meningitis (viral meningitis):
- Enteroviruses (such as coxsackie viruses and echoviruses)
- Herpes simplex virus (HSV)
Other microorganisms that can cause meningitis:
- Borrelia burgdorferi (Lyme disease)
- Fungi such as Candida, Aspergillus or Cryptococcus neoformans
Meningitis caused by a virus is more common and usually less severe. Bacterial meningitis usually is more severe and may produce long-term complications or death.
The organisms that cause meningitis usually colonize in a person's respiratory tract and may be transmitted by close contact with people who may be carrying the infection, or by touching contaminated objects such as doorknobs, hard surfaces or toys, and then touching the nose, mouth or eyes. The organisms also may be transmitted through respiratory secretions from a sneeze, close conversation or by touching infected matter.
The infection usually starts in the respiratory tract and then travels into the bloodstream where it can reach the brain and spinal cord. The organism may first cause a cold, sinus infection or ear infection (more common in children), and then travel through the sinuses into the brain and CSF, although this method of transmission is less common. A child may have no symptoms at all, but may carry the organism in his or her nose and throat.