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Meningitis, an infection of the subarachnoid space and leptomeninges
caused by a variety of pathogenic organisms, continues to be an
important source of mortality and morbidity. Despite the introduction
of new vaccines that prevent the most severe causes, bacterial, or purulent,
meningitis remains the most important form in the United
States in terms of incidence, sequelae, and ultimate loss of productive life. Aseptic
meningitis, usually caused by viruses, especially enteroviruses
(see Chapter 306) is more common; however,
significant sequelae are uncommon and the disease is usually self-limited. Granulomatous
meningitis, caused either by M tuberculosis or
fungi, is a major cause of neurologic injury and death in the developing
world (See Chapter 269).
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The first month after birth represents the period of highest
attack rate for meningitis, with likely pathogens including group
B streptococci (Streptococcus agalactiae), Escherichia coli, other
gram-negative enteric organisms, and less commonly, Listeria
monocytogenes (Table 231-1). Beyond
the neonatal period, the most important pathogens are Streptococcus
pneumoniae and Neisseria meningitidis. Formerly, Haemophilus
influenzae type b (Hib) was the most common
pathogen causing meningitis in infants and children, but the incidence
has been reduced substantially by immunization with conjugate vaccines
in developed countries.1,2 Recent studies of conjugate
pneumococcal vaccine, introduced in the United States in 2000, demonstrate
that it is effective in preventing pneumococcal meningitis.3 Similarly,
the meningococcal polysaccharide vaccine introduced in the early 1970s
has been effective in reducing meningococcal meningitis. Thus, the
incidence of infection and prevailing predominant causative organisms
varies depending upon the immunization status of the population.
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Bacterial meningitis is reported with increased frequency among
African Americans, Native Americans, and individuals in rural areas.
It is unclear whether environmental or genetic factors are responsible
for enhanced susceptibility. Seasonal patterns of disease have been
noted to occur, with meningitis caused by N meningitidis and S
pneumoniae peaking in the winter months, Hib showing
a biphasic distribution with peaks in the early winter and spring,
and L monocytogenes occurring most frequently in
the summer months. In the “meningitis belt” of
sub-Saharan Africa, the shift from the wet to the dry season is
associated with an increase in meningitis. These patterns are likely
due to the modes for acquiring the organisms, with N meningitidis, S
pneumoniae, and Hib spread by the respiratory
route, in months with increased ...