Bacterial infections of the leptomeninges and subarachnoid space, frequently involving the cerebral cortex, cranial nerves, cerebral blood vessels, spinal cord and nerve roots; causative organism varies with age and clinical status (eg, postoperative, immunodeficient, posttraumatic states); clinical manifestations include the acute onset of fever, stiff neck, altered mentation, seizures, and focal neurologic deficits; death may occur within 24 hours of disease onset; pathologic features include a purulent exudate in the subarachnoid space, and diffuse inflammation of neural and vascular structures.