Organism

Bacterial meningitis

Neonate: Group B streptococci (GPC) (70%), L. monocytogenes (GPR) (20%), S. pneumoniae (GPC) (10%), E. coli (GNR) and Klebsiella sp. (GNR) (1%), and other streptococci.

Infant: S. pneumoniae (GPC) (47%), N. meningitidis (GNDC) (30%), group B streptococci (GPC) (18%), Listeria monocytogenes (GPR), H. influenzae (GNCB) (due to vaccination, now very rare).

Child: N. meningitidis (60%), S. pneumoniae (25%), H. influenzae (now very rare) , and other streptococci.

Adult: S. pneumoniae (60%), N. meningitidis (20%), L. monocytogenes (6%), group B streptococci (4%), other Hemophilus sp., and staphylococci (1%) , Ehrlichia chaffeensis (rare).

Postneurosurgical: S. aureus (GPC), S. pneumoniae, P. acnes (GPR), coagulase-negative staphylococci (GPC), pseudomonas (GNR), E. coli (GNR), other Enterobacteriaceae, Acinetobacter (GNR).

Alcoholic patients and the elderly: In addition to the adult organisms, Enterobacteriaceae, pseudomonas, H. influenzae.

Immunocompromised: as above, L. monocytogenes .