Interpretation of positive molecular tests of common viruses in the cerebrospinal fluid.

Many central nervous system infections are historically difficult to diagnose. Polymerase chain reaction (PCR) has revolutionized the diagnosis of these infections because of their high sensitivity despite the lack of data on clinical usefulness. We conducted a retrospective study that included patients with positive cerebrospinal fluid (CSF) PCR for herpes simplex virus, varicella-zoster virus, JC virus, cytomegalovirus (CMV), and Epstein-Barr virus (EBV) between January 2009 and December 2011. The positive results were grouped into definite, likely, and possible true positives and likely false-positive categories based on pre-specified definitions specific to each virus. Of 1663 CSF viral PCR tests, 88 were positive (5%). The combined positive predictive value (PPV) was 58%. The PPVs were least for CMV and EBV at 29 and 37%, respectively. A positive CSF viral PCR result has to be interpreted with caution due to several false-positive results.