Viral meningitis

Most infections are acute and the commonest pathogens are viruses, especially in children and young adults. Patients with viral meningitis often present with an influenza-like illness with headache, sore throat and muscle pains. The features of meningitis then follow but tend to be milder than in bacterial infections and less rapid in onset. The common causes are the herpesviruses (family Herpesviridae) herpes simplex virus (HSV), varicella zoster virus and Epstein–Barr virus; the enteroviruses (family Picornaviridae) echovirus, coxsackievirus and mumps virus; and the Flaviviridae family, which includes West Nile virus and Japanese encephalitis virus.

Most viral meningitis resolves completely without specific treatment. However HSV meningitis, which occurs after primary HSV2 infections or in HSV reactivations in the immunosuppressed and elderly, requires intravenous aciclovir treatment.

Enteroviruses, HSV and mumps are common causes of viral meningitis. The most prominent manifestation of mumps is, however, parotitis. Epididymo-orchitis may, uncommonly, result in sterility; thyroiditis, pancreatitis, meningo-encephalitis, myocarditis and arthritis are rare complications.

Bacterial meningitis

In contrast to viral forms, bacterial meningitis may be life threatening and have serious sequelae for those who survive. While it may be impossible to predict the causative agent from the clinical features, some pathogens are more common at certain ages (Fig. 3.16.1). Neonatal meningitis may be early (within 7 days of birth) or late (occurring between 1 week and 3 months) onset. Early infections are acquired from the mother, whereas late infections may result from cross-infection after birth. The commonest causes of early-onset disease are group B β-haemolytic streptococci and coliforms such as Escherichia coli. Listeria monocytogenes and group B β-haemolytic streptococci can cause late-onset disease. Most bacterial meningitis occurs in childhood. The introduction of Hib vaccine against type B strains of Haemophilus influenzae has significantly reduced the incidence of invasive infections caused by this organism. The commonest cause is now Neisseria meningitidis. The three common serotypes A, B and C vary in prevalence, but B and C are commonest in western Europe and A in Arabic countries. The introduction of conjugated meningococcal C vaccine in the UK significantly reduced the incidence of meningococcal meningitis. Meningitis caused by Streptococcus pneumoniae occurs at all ages but particularly in children under 2 years, the elderly and those with immune defects (e.g. HIV infection, sickle-cell disease and postsplenectomy). Meningitis in adolescents and young adults is most commonly caused by meningococci. In later life, pneumococci are more likely. L. monocytogenes is a relatively rare cause but should be considered particularly in pregnant and immunocompromised patients. Tuberculous meningitis occurs more commonly in immigrants from developing countries.