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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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Etiology

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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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Table 232-1. Important Causes of Viral Meningitis and Encephalitis in North America
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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 ...

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