Epidemiology

Viral meningitis is one of the most common infections of the central nervous system. It is difficult to estimate the number of cases because symptoms are often so mild they are mistaken for flu, and many cases do not undergo diagnostic lumbar puncture. Viral meningitis affects all ages but is most commonly diagnosed in children. Although most cases resolve without treatment, viral meningitis is responsible for a significant number of hospitalizations. In the US in 2006, approximately 40,000 people with viral meningitis were admitted to hospital.[6] No difference in incidence has been described among people of different ethnic groups. Males appear to be affected more commonly than females.[7][8] Enteroviruses are responsible for the majority of cases.[9][8] In temperate climates the incidence of enteroviral meningitis shows marked seasonal variation with peaks in summer and autumn months. Arboviruses are responsible for a substantial proportion of nonenteroviral viral meningitis. In North America the incidence of arboviral infection is maximal in the summer and fall when the mosquito or tick vectors are most active. Many arboviruses are confined to a particular geographic area; this range may change, as the emergence of the West Nile virus infection in Europe and North America demonstrates.[10][11][12]

Risk factors

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infants and young children

Enteroviral meningitis most commonly affects children under 5 years old.[4][21]​​ Symptoms in children generally abate within 1 week; adults may have a more prolonged clinical course.[2]

young adults

Herpes simplex follows a bimodal age distribution with infection in young adults as a result of primary exposure and in older adults as a result of waning immunity.

older people

Herpes simplex follows a bimodal age distribution with infection in young adults as a result of primary exposure and in older adults as a result of waning immunity.

summer and fall

In temperate regions enteroviral meningitis shows a marked seasonality with more cases seen in summer and fall.[21][22]

exposure to mosquito or tick vector

Infections with arboviruses are more common when contact with the mosquito or tick vectors is more likely.

unvaccinated for mumps

Meningitis is a common manifestation of mumps occurring in up to 10% of cases.[15] Mumps is now uncommon in vaccinated populations.

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use of swimming pools and ponds

Outbreaks of enteroviral meningitis have been associated with the use of swimming pools and ponds.[23]

immunosuppression

Impaired cell-mediated immunity is associated with an increased risk of viral meningitis, in particular infection with cytomegalovirus (CMV) and varicella zoster virus.[24][25]​​ Agammaglobulinemia is associated with chronic infection with echovirus-11.​[26]​​

exposure to rodents

Lymphocytic choriomeningitis virus is carried by rodents such as hamsters, mice, and rats. Close contact with infected animals may lead to an influenza-like illness, which may include meningitis.

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