Meningitis is an infection and inflammation of the membranes (the meninges) surrounding the brain and spinal cord. It can be caused by a reaction to certain medications or medical treatments, an inflammatory disease such as lupus, some types of cancer, or a traumatic injury to the head or spine. The most common cause, however, is an infection by a virus, bacterium, parasite, or fungus, according to the National Institute of Neurological Disorders and Stroke (NINDS).
Meningitis caused by an infection usually begins when the infection passes from its original site—for example, the upper respiratory tract—into the bloodstream and then into the cerebrospinal fluid that surrounds the brain and spinal cord. From there, it travels to the brain and/or the surrounding membranes, called the meninges. Sometimes the bacteria or viruses infect the meninges directly.
The seriousness of the infection and the best treatment depend on the cause, according to the National Meningitis Association (NMA). With bacterial meningitis, delaying treatment increases the risk for permanent brain damage or death. Viral meningitis, also called aseptic meningitis, is the most common form of meningitis in the United States. It is rarely fatal. Viral meningitis may also include inflammation of the brain itself.
The most common causes of bacterial meningitis are group B streptococcus, found in newborns; Haemophilus influenzae, now prevented with a vaccine; Streptococcus pneumonia, which causes pneumococcal meningitis, the most common and serious form of this illness; and Neisseria meningitides, which causes meningococcal meningitis, a high contagious form that is more likely to affect children. Less common bacterial causes are Listeria monocytogenes; Escherichia coli, which is more common in elderly adults and newborns; Mycobacterium tuberculosis; and Staphylococcus aureus.
Viral meningitis is usually caused by enteroviruses. These are common viruses that enter the body through the mouth and travel to the brain and surrounding tissues, where they multiply. Enteroviruses are present in mucus, saliva, and feces and can be transmitted through direct contact with an infected person or an infected object or surface.
Viruses that can cause meningitis include varicella zoster, the virus that causes chickenpox and shingles; influenza viruses, mumps virus, HIV, arboviruses, which cause diseases such as West Nile and eastern equine encephalitis; and herpes simplex virus. Fungi and parasites also can cause meningitis.
Signs and symptoms
The early signs and symptoms of meningitis are easily mistaken for the flu, the NMA says. They may develop over a period of a day or two, but some types of meningitis can prove fatal within 24 hours after symptoms appear.
Seek medical care right away if someone has any of these signs or symptoms:
Sudden high fever
Sudden severe headache
Stiff neck that's related to a headache
Confusion or seizures
Sleepiness or difficulty waking up
Sensitivity to light
Several risk factors can make you or your child more likely to be infected with meningitis:
Age. Newborns of mothers infected with group B strep, children younger than 5 years, and young adults ages 18 to 24 are at higher risk. (Elderly adults also are at higher risk.)
Living in a community setting. College students living in dormitories, personnel on military bases and children in boarding schools and child-care facilities are at increased risk for meningitis.
Most viral meningitis is a seasonal illness. It's more common during the summer and early fall than at other times of the year.
The complications of meningitis can be severe and include hearing loss, blindness, learning disabilities, brain damage, and paralysis. Whether complications occur depends on a person's age, his or her immunity, the type of bacteria, virus, or other pathogen involved, and how quickly treatment is started.