Serious infection of the meninges, the outer membranes covering the brain and spinal cord

Aetiology

Bacterial meningitis

Age-specific common causes

• ­Neonates: Listeria monocytogenes, group B Streptococci, E. coli
• ­Infants and young children: H. influenza
• ­Ages 10 to 21: Neisseria meningitidis, Streptococcus pneumoniae
• ­Age over 21: Streptococcus pneumoniae, Neisseria meningitidis
• ­Over 65 : Streptococcus pneumoniae, Listeria monocytogenes

Causes associated with specific patient factors

• ­Decreased cell-mediated immunity: Listeria monocytogenes
• Neurosurgery/ head trauma: Staphylococcus, Gram negative bacilli (Klebsiella pneumoniae, E.coli, Pseudomonas aeruginosa)
• Fracture of the cribiform plate: Streptococcus pneumoniae

Viral meningitis

• Most common cause of meningitis
• Common causative organisms include: enteroviruses (echovirus, Coxsackievirus), mumps, HSV and herpes zoster virus, HIV, measles, influenza, arboviruses
  • Enteroviruses are the most common cause of meningitis in immunocompetent adults in the UK

Aseptic meningitis

• CSF has cells but is Gram-stain negative and no bacteria can be cultured on standard media
• Viral meningitis will be aseptic
• Other (rarer) causes include fugal infection, parasites, atypical TB, syphilis, Lyme disease, Kawaskaki disease