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Meningitis is defined as an inflammation of the leptomeninges. Causes of meningitis are summarized in Table 19-1. Bacteria cause meningitis by invading and replicating in the subarachnoid space, causing significant morbidity and mortality. Although viruses, most commonly enteroviruses, also cause meningitis, few children with viral meningitis suffer any long-term sequelae. Therefore, the focus of this chapter is on bacterial meningitis.

TABLE 19-1Etiology of Meningitis

Overall, there has been a remarkable decline in the rate of bacterial meningitis in the developed world with the introduction of the Haemophilus influenzae type b conjugate vaccines and the Streptococcus pneumoniae conjugate vaccines, and greater use of meningococcal vaccines.1 Haemophilus influenzae type b was once the leading cause of bacterial meningitis in children but has been virtually eliminated in countries utilizing the conjugate vaccine. In the first 2 months of life enterobacteriaceae (e.g., E. coli, Klebsiella spp.), group B Streptococcus, and occasionally Listeria monocytogenes, Salmonella spp., or enterococci cause bacterial meningitis. Infections due to Streptococcus pneumoniae and Neisseria meningitidis occur with increasing frequency over the second month to become the most likely cause of bacterial meningitis. Neisseria meningitidis is the most common cause of bacterial meningitis by one year of age. Streptococcus pneumoniae remains the second most common cause after one year of age, and all other pathogens trail behind (Table 19-2). These two pathogens occur more commonly in the winter months, presumably in association with common respiratory viruses that disrupt mucosal barriers, thereby allowing these colonizing pathogens to move from the nasopharynx to the bloodstream more easily.2

TABLE 19-2Causes of Bacterial Meningitis by Age Group

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