The patients with diabets mellitus, malignancies and those on immunosuppressive drugs have reduced resistance and are more susceptible to develop meningitis due to infection with Eisteria monocytogenes and mycoplasma pneumoniae, etc, The infection is more common in infants and young children because their immune mechanism and phagocytic functions are not fully matured. Meningitis may follow upper respiratory infection, otitis media, Pyoderma and head injuries.
The infection may spread to meninges from other sources such as nasopharynx, the organism invade surrounding blood vessels and enter the cerebrospinal fluid spreading throughtout the subarachnoid space. As a result of inflammatory process, there is an increase in cerebrospinal fluid (CSF) exudate in the ventricles and interference in the CSF flow throughout the ventricular aqueduct. The fluid in subarachnoid spaces may be cloudy or opaque or purulent depending upon the type of organism identified. Ependymal cells are also destroyed and purulent exudate collects at the base of the brain. Thrombophelbitis of cerebral vessels may occur leading to infection and cerebral damage and cranial nerves may also be affected, resulting in deafness, blindness, and weakness or paralysis of the muscles of the face and neck.