Ruling Out Bacterial Meningitis in Patients with CSF Pleocytosis

With widespread use of Haemophilus influenzae type b and pneumococcal vaccines in the U.S., bacterial meningitis has become far less common in children. These authors previously developed a clinical prediction rule (the Bacterial Meningitis Score) to classify risk for bacterial meningitis in children with cerebrospinal fluid (CSF) pleocytosis and validated it at a single site. Now they report the results of a retrospective validation study at 20 U.S. academic medical centers.

They reviewed the charts of patients aged 29 days to 19 years who presented from 2001 to 2004 with CSF pleocytosis (≥10 white blood cells/µL, corrected for CSF red blood cells using a ratio of 1 WBC per 500 RBCs). The prediction rule classifies patients as being at low risk for bacterial meningitis if they have none of the following criteria: positive CSF Gram stain, CSF absolute neutrophil count (ANC) ≥1000 cells/µL, CSF protein ≥80 mg/dL, peripheral blood ANC ≥10,000/µL, and history of seizure before or at presentation. Patients with CSF pleocytosis who required hospital admission (e.g., had sepsis or were immunocompromised) were excluded from the study, regardless of their risk for meningitis. Bacterial meningitis was diagnosed when a patient had a positive CSF culture, CSF pleocytosis with a positive blood culture for a bacterial pathogen, or CSF pleocytosis with a positive CSF latex agglutination test for a bacterial pathogen.

Of 3295 patients with CSF pleocytosis, 3.7% had bacterial meningitis, and 96.3% had aseptic meningitis. Only 2 patients were misclassified as being at low risk. Both patients were younger than 2 months and had Escherichia coli isolated from CSF and urine, despite negative urinalyses at presentation. Overall, the negative predictive value of the rule for patients categorized as very low risk for bacterial meningitis was 99.9%. Positive CSF Gram stain was the strongest predictor of bacterial meningitis (odds ratio, 866).