Diagnostic accuracy of cerebrospinal fluid gram stain for bacterial meningitis in patients with a suspected central nervous system infection.

OBJECTIVES

Bacterial meningitis is a life-threatening disease requiring rapid pathogen identification and prompt initiation of treatment. Cerebrospinal fluid (CSF) Gram stain is a widely recommended, rapid diagnostic test, yet its diagnostic accuracy in unselected patients with suspected central nervous system (CNS) infection remains insufficiently defined.

METHODS

We assessed the diagnostic accuracy of CSF Gram stain for bacterial meningitis in patients aged ≥16 years old who underwent a lumbar puncture for a suspected CNS infection. The reference standards were microbiologically confirmed bacterial meningitis, and a clinical diagnosis of bacterial meningitis as scored by two physicians.

RESULTS

Among 1637 episodes, CSF Gram stain was performed in 1226 (75%), in which bacterial meningitis was microbiologically confirmed in 135 (11%) cases and clinically diagnosed in an additional 53 episodes (4%). The sensitivity of CSF Gram stain was 53% (95% CI: 42-59) for microbiologically confirmed meningitis and 38% (95% CI: 31-46) for clinically diagnosed meningitis, whereas specificity was 100% in both groups. In 16 CSF culture-negative cases, Gram stain identified a bacterial pathogen in CSF. Antibiotic treatment was adjusted within 24 hours more frequently in bacterial meningitis patients with a positive CSF Gram stain compared with those with a negative results (20 of 68 [29%] vs. 11 of 114 [10%], p <0.001).

CONCLUSIONS

CSF Gram stain has excellent specificity but low sensitivity for the diagnosis of bacterial meningitis in patients with a suspected CNS infection. Although positive results reliably confirm disease, the impact on clinical management is modest.