Dittrich T, Marsch S, Egli A, et al. - Cerebrospinal fluid (CSF) analyses are recommended in patients with meningitis and/or encephalitis, but there is low evidence concerning its diagnostic yield. Researchers here investigated predictors of infectious pathogens in the CSF of adult patients presenting with meningitis, and/or encephalitis. In this cross-sectional study, inclusion of 372 patients from 2011–17 at a Swiss academic medical care center, was performed. Among these, infections were diagnosed in 42.7% presenting as meningitis (51%), encephalitis (32%), and meningoencephalitis (17%). Following were the most frequent infectious pathogens: Streptococcus pneumoniae, Varicella zoster, and Herpes simplex 1&2. Multivariable analysis revealed lactate concentrations and decreased glucose ratios as the only independent predictors of bacterial infection and increased CSF mononuclear cells as the only predictors of viral infections. All predictors revealed good calibration. These findings suggest a possible utility of CSF data in guiding clinicians when infection is suspected prior to microbiologic workup, while other laboratory and neuroradiologic characteristics appear less useful.