Diagnosis of bacterial meningitis

To diagnose bacterial meningitis, CSF examination is mandatory. CSF culture remains the gold standard for the diagnosis of bacterial meningitis; aerobic culturing techniques are obligatory for community-acquired bacterial meningitis. Anaerobic culture may be important for post-neurosurgical meningitis or for the investigation of CSF shunt meningitis. In a retrospective series of 875 community-acquired bacterial meningitis patients for whom the diagnosis was defined by a CSF white blood cell count of over 1,000 cells per mm3 and/or more than 80% polymorphonuclear cells, the CSF culture was positive for 85% of cases in the absence of prior antibiotic treatment.5

 

CSF culture is obligatory to obtain the in vitro susceptibility of the causative microorganism and to rationalize treatment. CSF Gram staining, latex agglutination testing and PCR are additional diagnostic tools that might aid in etiological diagnoses, especially for patients with negative CSF cultures (i.e., after antibiotic pretreatment).6 Characteristic CSF findings for bacterial meningitis consist of polymorphonuclear pleocytosis, hypoglycorrhachia, and raised CSF protein levels. A prediction model based on 422 patients with bacterial or viral meningitis showed that individual predictors of community-acquired bacterial meningitis were a glucose concentration of less than 1.9 mmol per liter (0.34 g/liter), a ratio of CSF glucose to blood glucose of less than 0.23, a protein concentration of more than 2.2 g per liter, or a white cell count of more than 2,000 cells per mm3.7