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INTRODUCTION AND EPIDEMIOLOGY
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Meningitis is an inflammation of the leptomeninges, tissues that cover the brain and spinal cord. Untreated bacterial meningitis has a mortality of nearly 100%, so treat suspected bacterial meningitis promptly. Unfortunately, even with rapid antibiotic treatment, long-term neurologic sequelae occur. Viral meningitis has a range of severity. Mild cases resolve without sequelae. However, some viruses, such as herpes virus, can cause severe infections. Meningoencephalitis is an inflammation of the brain as well as the meninges. It is less common than meningitis but can be devastating.
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The most common causes of bacterial meningitis vary with the child's age. In neonates, important organisms are group B Streptococcus, Escherichia coli, and Listeria monocytogenes. Other gram-negative bacteria can be occasional causes of meningitis as well. In infants >1 month old and children, the leading organisms are Neisseria meningitides, Streptococcus pneumoniae, and Haemophilus influenzae type b. Vaccination programs have had a huge impact on the epidemiology of bacterial meningitis in developed countries. Prior to the widespread use of H. influenzae type b (Hib) conjugate vaccines, H. influenzae type b was the most common cause of bacterial meningitis in children in the United States. Since the introduction of Hib vaccines, the incidence of H. influenzae type b meningitis has decreased by 99% in the United States.1 Similar dramatic decreases have occurred in other developed countries. Immunization has also had a big impact on the incidence of meningitis from S. pneumoniae in the United States and other developed countries. At present, the primary cause of bacterial meningitis in the United States is N. meningitides.2 Other important causes of bacterial meningitis in children include Mycobacterium tuberculosis and Borrelia burgdorferi, the causative agent of Lyme disease.
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Viral meningitis is fairly common. Enteroviruses are the most frequent cause. Meningoencephalitis can be caused by enteroviruses, arboviruses (including West Nile virus), and herpes viruses. Herpes simplex virus type 1 (HSV-1) infection occurs sporadically and causes a severe meningoencephalitis in children and adults. Herpes simplex virus type 2 (HSV-2) develops in neonates born to infected mothers. Varicella-zoster virus can cause CNS infections including acute cerebellar ataxia. Many other viruses can cause CNS infections, including cytomegalovirus, Ebstein-Barr virus, mumps virus, adenovirus, influenza virus, parainfluenza virus, rubeola virus, rubella virus, and rabies virus.
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Fungal meningitis can occur in both normal and immunocompromised hosts. Important causes include Cryptococcus neoformans, Coccidioides immitis, and Candida albicans.
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Parasite infections can cause eosinophilic meningitis, defined as meningitis with at least 10 eosinophils/mm3 of cerebrospinal fluid (CSF).3 The most frequent cause of eosinophilic meningitis throughout the world is helminth infection.
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Bacterial meningitis in children usually results from bacteremia, arising from organisms colonizing the nasopharynx. Less commonly, meningitis is caused by direct spread of bacteria from a contiguous site of infection, such as sinusitis, or from penetration ...