Identifying the agent responsible for suspected cases of viral central nervous system (CNS) infection poses tremendous diagnostic challenges, and a specific organism is identified in only ∼30% of cases of suspected viral encephalitis.¹ Traditionally, definitive diagnosis has depended on: 1) culture of virus from cerebrospinal fluid (CSF) or brain tissue; 2) identification of viral particles, inclusions, antigen, or nucleic acid in brain tissue; or 3) demonstration of virus specific intrathecal antibody synthesis.

The ability to amplify small amounts of viral nucleic acid from CSF using the polymerase chain reaction (PCR) technique has revolutionised the diagnosis of viral CNS infections. CSF PCR is rapid, inexpensive, and only minimally invasive. Unfortunately, validation of the sensitivity and specificity of CSF PCR by comparison to a “gold standard” such as brain biopsy, is only rarely available.^2,3 False positive CSF PCR …