Organism | Site of entry | Age range | Predisposing conditions |
Neisseria meningitidis | Nasopharynx | All ages | Usually none, rarely complement deficiency |
Streptococcus pneumoniae | Nasopharynx, direct extension across skull fracture, or from contiguous or distant foci of infection | All ages | All conditions that predispose to pneumococcal bacteremia, fracture of cribriform plate, cochlear implants, cerebrospinal fluid otorrhea from basilar skull fracture, defects of the ear ossicle (Mondini defect) |
Listeria monocytogenes | Gastrointestinal tract, placenta | Older adults and neonates | Defects in cell-mediated immunity (eg, glucocorticoids, transplantation [especially renal transplantation]), pregnancy, liver disease, alcoholism, malignancy |
Coagulase-negative staphylococci | Foreign body | All ages | Surgery and foreign body, especially ventricular drains; dermal sinus |
Staphylococcus aureus | Bacteremia, foreign body, skin | All ages | Endocarditis; surgery and foreign body, especially ventricular drains; cellulitis; dermal sinus; decubitus ulcer |
Gram-negative bacilli | Various | Older adults and neonates | Advanced medical illness, neurosurgery, ventricular drains, disseminated strongyloidiasis |
Haemophilus influenzae | Nasopharynx, contiguous spread from local infection | Adults; infants and children if not vaccinated | Diminished humoral immunity |
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