Meningitis (or spinal meningitis as it commonly known) is an infection in the meninges and cerebrospinal fluid. The meninges are three thin layers of membrane that cover the brain and spinal cord. Cerebrospinal fluid is watery layer of cushion just beneath the meninges that bathes and protects the brain and spinal cord from physical impact.
Meningitis is usually caused by either a bacteria or virus. Viral meningitis is generally self-limitingmeaning that it disappears on its own without any treatment. Bacterial meningitis, on the other hand, can be quite severe and can lead to permanent hearing loss, learning disability, or other types of brain damage.
There are several different bacterial strains that can cause meningitis, some of which can be readily treated with antibiotics. HIV (human immunodeficiency virus) can cause meningitis, but the condition actually is caused by a fungus, and not HIV itself.
Most people who are infected with a bacteria or virus that could potentially cause meningitis never actually get sick. For example, according to the Meningitis Research Foundation, for every 1000 people who are infected with a meningitis virus, only one person will actually become ill. The same is true of bacterial meningitis. It is not clear these few people actually develop meningitis from microorganisms and viruses that are apparently harmless to most people. It is likely due to a weakness in the immune system.
Types & Causes of Meningitis
Viral meningitis, also known as aseptic meningitis, is the most common type of meningitis and is caused by an infection of one of several different types of viruses. Viral meningitis is serious but rarely fatal.
Symptoms usually last no more than about 10 days, and then the person recovers fully, even without treatment. The viruses that cause viral meningitis are contagious and are very common in the summer and early fall, but most people exposed to one of the viruses do not develop symptoms.
Sometimes a person may develop a cold or a rash, but full-blown meningitis develops in fewer than 1 in 1000 people who are infected with a meningitis virus. Consequently, if you are around somebody who has viral meningitis, you have a very small chance of developing it yourself, even if you get infected. About 90 percent of all viral meningitis cases involve a type of virus known as an enterovirus. The mumps and herpes viruses can also cause meningitis.
There are several different types of bacteria that can cause bacterial meningitis. It is important to identify the bacteria so that an appropriate antibiotic can be prescribed. Bacterial meningitis can progress quickly and can lead to death, so it is essential that it be diagnosed and treated as soon as possible.
Some forms of bacterial meningitis are contagious and are spread through secretions from the mouth or nose, although they are not nearly as contagious as the common cold or flu. They are not spread by casual contact. However, people living in crowded households or chronic care facilities are at greater risk for developing bacterial meningitis.
There are vaccines for some types of bacterial meningitis. Infants in the United States are routinely vaccinated for the Hib strain. Outbreaks of meningitis epidemics do occur throughout the world, although they are rare in the United States.
Cryptoccal meningitis is a type of meningitis that develops in people with HIV and is caused by a fungus. The course of the illness is often a slow one, with symptoms that may progress over days to weeks to even months.
No matter what causes meningitis, the symptoms are the same. The most common symptoms include headache, stiff neck, and fever. In infants, these symptoms may be difficult to detect. Other symptoms include vomiting, nausea, photophobia (sensitivity to light), confusion, sleepiness, and seizures. Some people may develop a skin rash or joint pain. Some may have an upper respiratory infection or other illness before the symptoms of meningitis start to show.
The symptoms may develop over the course of a few hours or a few days. They usually occur much more quickly in bacterial meningitis and, if untreated, can lead to unconsciousness.
A clinical and neurological examination can be used to diagnose meningitis. One of the most telling clinical symptoms of meningitis is a stiff neck. It is extremely painful for a person with meningitis to move their neck forward. The neck may be so stiff that if they try to move it, their whole body moves instead. Other clinical signs include a skin rash and a swelling of the nerves in the eye, which indicates an increased pressure in the brain.
Imaging Studies (e.g., CT scan) may be done to view the brain and rule out other possible neurological disorders.
Both viral and bacterial meningitis are usually positively diagnosed by doing a spinal tap, or lumbar puncture, which involves inserting a needle into the lower back (the lumbar area of the spine) and collecting some cerebrospinal fluid. The fluid is then sent to a lab where it is examined under the microscope to identify the microorganism that is causing the infection.
Most forms of viral meningitis are self-limitingthey disappear on their own without treatment. Bacterial meningitis is a potentially life-threatening emergency that should be treated with antibiotics as soon as possible. If bacterial meningitis is suspected, antibiotics should be administered even before the spinal fluid is collected to confirm the diagnosis. Secondary symptoms, like changes in blood pressure, must be treated as well.