Table 1: Causative organisms.

Organism Comment   Streptococcus pneumoniae Commonest organism Affects healthy children Additional risk factors: basilar skull or cribriform fracture, asplenism, HIV, and cochlear implants   Neisseria meningitidis Can cause epidemic, endemic, or sporadic infections   Haemophilus influenzae type B Reduced incidence after introduction of vaccination program   Group B streptococcus The less common pathogens Group B streptococcus, E. Coli and L. monocytogenes more common in neonates   Escherichia coli   Non typeable H. influenzae   Other gram-negative bacilli   Listeria monocytogenes   Group A streptococci   Staphylococcal species Penetrating head trauma and neurosurgery   Streptococci     Aerobic gram-negative bacilli