Meningitis is inflammation of the membranes (meninges) covering the brain and the spinal cord. Although the most common causes are infection (either bacterial or viral), chemical agents and even tumor cells may cause meningitis. Encephalitis and brain abscess can complicate infective meningitis.
Causative organisms
Viruses are the most common cause of meningitis.
Major bacteria that cause meningitis are Neisseria meningitidis (meningococcus), Streptococcus pneumoniae (pneumococcus), and Haemophilus influenzae. Less common bacterial causes include Listeria monocytogenes, Staphylococcus and Escherichia coli. In developing countries, Mycobacterium tuberculosis is a common cause of bacterial meningitis.
In immunocompromised patients, fungal meningitis may occur, typically caused by Cryptococcus neoformans.
Non-infectious causes include: -
Tumors
Leukemia
Lymphoma
Brain tumors
Brain metastasis
Sarcoidosis
Drugs
Intrathecal drugs
Methotrexate
Lead poisoning
Incidence
20,000 to 25,000 cases of bacterial meningitis are seen in the United States every year. Mostly adults are infected, where it can be community acquired or nosocomial. Vaccination against Haemophilus influenzae has reduced the incidence in children.
Meningitis may occur in outbreaks in communities who have close contact with each other, such as in dorms or military establishments. In the large majority of such outbreaks, neisseria meningitidis is the etiologic agent.
Common Neurological Disorders
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