Description

• Clinical syndrome characterized by acute meningeal inflammation without an identifiable bacterial pathogen in the CSF.
• System(s) affected: Nervous
• Synonym(s): Abacterial meningitis, Aseptic meningitis

Epidemiology

• Estimated 26,000–42,000 hospitalizations each year in the US for viral meningitis (VM)
• In 2006, there were 72,000 meningitis-related hospitalizations, with 58% of those having meningitis as the primary reason for hospitalization. Of all 72,000 hospitalizations, 56.4% were determined to be viral cases (1)[A].
• More common than bacterial meningitis:
  • Annual incidence of viral meningitis is higher than total number cases of meningitis caused by all other etiologies combined.
• Peaks in late summer to early fall:
  • Enteroviruses and arthropod-borne viruses predominate in warm months.
  • Mumps usually occurs in the winter and spring, often in epidemics.
• Occurs in both outbreak and sporadic forms

Risk Factors

• Close contact with known cases of VM
• Immunocompromised hosts may be more susceptible to cytomegalovirus (CMV), herpes simplex virus (HSV), and adenovirus.
• Lymphocytic choriomeningitis virus (LCMV) is commonly transmitted via exposure to rodent feces, bodily fluids, or nesting materials:
  • Rodent bites and vertical transmission as mechanisms of infection are possible, but unconfirmed.

Geriatric Considerations
Cases of VM in the elderly are rare, but are documented. Consider alternative diagnoses (e.g., carcinomatous meningitis, NSAID- or medication-induced meningitis) in the elderly population.

Genetics
None

General Prevention

Limit exposure to known hosts; hand washing, and general hygiene.

Pathophysiology

• First described by Wallgren in 1925
• In immunocompetent hosts, VM is generally caused by a systemic viral infection with predilection to neurologic involvement.
• Less commonly, direct neural transmission occurs from a self-limited infection such as HSV already present in the immunocompetent host.

Etiology

• >90% of cases caused by enterovirus family, which includes coxsackievirus A and B, echovirus, poliovirus, and E# variants: E9 and E30 strains specifically implicated in eastern and western hemispheres, respectively.
• Less common causes include HSV-1 and HSV-2, varicella-zoster virus (VZV), adenovirus, LCMV, CMV, Epstein-Barr virus (EBV), HIV, and mumps
• Increasing frequency of neonatal morbidity and mortality associated with human parechovirus strains
• Recurrent (Mollaret's) meningitis shows 80% association with HSV-2.
• Arthropod-borne viruses: West Nile virus, St. Louis encephalitis virus, and California encephalitis virus
• Parvovirus B19 is found in the CSF of 4.3% of undiagnosed meningoencephalitis patients (2)[B].

Commonly Associated Conditions

Encephalitis; neurologic deficits; myopericarditis; neonatal enteroviral sepsis