Recent survey of infectious meningitis in adults: review of laboratory findings in bacterial, tuberculous, and aseptic meningitis.

Infectious meningitis in adults was reviewed to establish the frequency of meningitis due to each causative agent and to reexamine the laboratory parameters that help to distinguish aseptic, bacterial, and mycobacterial meningitis. Aseptic meningitis occurred 2.2 times more often than bacterial and mycobacterial meningitis combined. The most common nonviral causative agent was the pneumococcus (23 cases) followed by the tubercle bacillus (11 cases) and the meningococcus (5 cases). Cerebrospinal fluid (CSF) Gram stain was the most useful study to rule in a bacterial cause: 89% of cases of bacterial meningitis had a positive initial Gram stain. Hyponatremia occurred in 73% of cases of tuberculous meningitis; hyponatremia combined with a negative Gram stain was highly suggestive of a tuberculous cause. One third of all patients with tuberculous and aseptic meningitis had a predominance of neutrophils in the CSF. No patient with aseptic meningitis had a CSF while count higher than 2,800 cells/cu mm or a CSF protein value higher than 250 mg/100 ml. Other reviews confirm this if cases due to lymphocytic choriomeningitis (LCM) are excluded. One patient with tuberculous meningitis in this series, and none of those cases reviewed, had a CSF white count higher than 1,200 cells/cu mm. Only 3.7% of the patients with aseptic meningitis had hypoglycorrhachia. Series reporting exclusively disease due to mumps and LCM have a higher frequency of hypoglycorrhachia.