Background Varicella zoster virus (VZV) is a common cause of viral encephalitis with wide spectrum of morbidity and mortality. The pathophysiology remains poorly understood and few prognostic markers are available. A few studies have attempted to use the viral load of the cerebrospinal fluid (CSF), to investigate the pathophysiology and prognosis, with contradictory results. However, these studies have not assessed the viral load in the context of time.

Objectives To determine the CSF viral load in VZV encephalitis in relation to time and outcome.

Study Design The Liverpool Specialist Virology laboratory database was screened to identify patients with CSF positive for VZV over 5 years. Viral load was determined by qPCR. A poor outcome was defined as moderate disability to death (Glasgow outcome score 2–5).

Results 608 patients were screened, 36 had VZV PCR performed, 12 were positive and had clinical features consistent with encephalitis. There was a strong negative correlation between the time from symptom onset to LP and the viral load (τ b=−0.59, p=0.036). There was no significant difference in viral load between those with good and poor outcome.

Conclusions In this study of VZV encephalitis, CSF viral load appears to more closely relate to time of LP from symptom onset than to outcome. Timing of LP should be taken into account in future studies of viral encephalitis which aim to relate viral load to outcome in viral encephalitis.