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Viral infections of the central nervous system (CNS) may be variously
categorized by type of onset (ie, acute, subacute, recurrent, or
chronic), by the level of the CNS involved (ie, brain, brain stem,
or spinal cord), and by the viral agent causing disease. The approach
to diagnosis and management of CNS viral infection depends greatly on
the age, immunization history, and immune status of the patient,
and also the epidemiologic setting including season, location, and
exposure to viruses that are circulating in the community or transmitted
by arthropod vectors.
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Acute Viral Meningitis
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Community-acquired viruses and arthropod-borne viruses are the
major causes of the acute “aseptic meningitis” syndrome
that, by definition, is accompanied by symptoms and signs of meningeal
inflammation in the absence of acute bacterial or fungal meningitis.
Although meningitis may occur in the course of infection with many
viruses (Table 232-1), the human enteroviruses
have been shown to be responsible for the majority of cases of viral meningitis,
most prominently the group B enteroviruses, polioviruses, and enterovirus
71. Other well-known causes of viral meningitis include mumps virus,
lymphocytic choriomeningitis virus, herpes simplex virus, and the
arthropod-borne viruses (including West Nile virus, St. Louis encephalitis
virus, La Cross virus, and eastern equine encephalitis virus).
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Because enteroviruses cause more than 90% of cases,
even during periods of peak arbovirus transmission, the epidemiology
of viral meningitis usually reflects the trends of enterovirus infection
in the population, including seasonal peaks in late summer and fall
and a strong inverse correlation between age and observed rates
of disease. Overall rates of enterovirus infection are severalfold
higher for infants under 12 months of age than older children. The
observed rates of meningitis among children with documented enterovirus
infection are highest under 4 months of age when approximately 50% of
infants undergoing lumbar puncture in the course of an evaluation
for fever will have laboratory evidence of meningitis.1
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Mumps virus infection, once a common cause of viral meningitis,
is now seen only in locations where mumps virus circulation is not controlled
by immunization (see Chapter 318). More than ...