CLINICAL CHARACTERISTICS AND OUTCOMES IN ADULTS WITH BACTERIAL MENINGITIS AND NEGATIVE CEREBROSPINAL FLUID CULTURES

Ten to thirty percent of patients with bacterial meningitis have negative CSF cultures, yet their clinical characteristics and outcome remain poorly defined.

Between 2006 and 2023, adults with bacterial meningitis were prospectively included in a nationwide cohort study. Patients with negative CSF cultures were compared to those with positive CSF cultures. Outcome was assessed using the Glasgow Outcome Scale, with scores of 1-4 classified as unfavourable. CSF samples from microbiology-negative patients underwent additional testing with the IS-pro assay, a broad-spectrum PCR technique.

CSF cultures were negative in 413 of 3,132 episodes (13%). A pathogen was identified in 328 (80%) through blood culture, CSF bacterial PCR, or antigen testing, leaving 85 episodes without microbiological confirmation. Patients with negative CSF cultures more often received pre-admission antibiotics (13% vs 10%, p=0.02) and had lower rates of unfavourable outcome (29% vs 39%, p<0.001). Blood cultures were positive in 53%, and CSF PCR detected a pathogen in 49%. The IS-pro assay detected Streptococcus pneumoniae (n=5), Streptococcus bovis group/Streptococcus intermedius (n=5), and Streptococcus constellatus (n=1).

Bacterial meningitis patients with negative CSF cultures have more favourable outcomes. Combining CSF cultures with blood cultures and CSF PCR improves pathogen detection, while broad-spectrum PCR may help identify atypical pathogens.