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III. Meningitis (Leptomeningitis)

A. Pathogenesis:

Hematogenous spread of organisms from primary infection in lungs or elsewhere in body;  including infection by organisms in birth canal and aspiration of contaminated amniotic fluid.

Direct inoculation: secondary to trauma  or iatrogenic (e.g. introduction of organism into CSF during lumbar puncture in patient with septicemia).

Direct spread from contiguous infection.

B. Etiologic Agents:

  • Bacteria are the most common. In general, pneumococcal and meningococcal meningitis are the most common types, but there is distinct variation by age group. In neonates, two of the most common organisms are Escherichia coli and the group B streptococci. In the elderly, Streptococcus pneumoniae and Listeria monocytogenes are common.
  • Viruses, spirochetes, fungi, and M. tuberculosis are less common agents.