Aetiology of meningitis

The most common causes of bacterial meningitis are Streptococcus pneumoniae and Neisseria meningitidis. In young children who are not fully vaccinated, Haemophilus influenzae type b (Hib) is also common. In neonates and children younger than 2 months, Streptococcus agalactiae (group B streptococcus), Escherichia coli and other aerobic gram-negative bacilli are important pathogens. Listeria monocytogenes is more common in adults older than 50 years, neonates and patients with immune compromise.