Table 1: Causative organisms.

OrganismComment

Streptococcus pneumoniaeCommonest organism
Affects healthy children
Additional risk factors: basilar skull or cribriform fracture, asplenism, HIV, and cochlear implants

Neisseria meningitidisCan cause epidemic, endemic, or sporadic infections

Haemophilus influenzae type BReduced incidence after introduction of vaccination program

Group B streptococcusThe 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 speciesPenetrating head trauma and neurosurgery
Streptococci
Aerobic gram-negative bacilli