Aim: To investigate the sensitivity of various laboratory approaches in the diagnosis of herpes zoster from patient serum.
Methods: Paired sera from 53 consecutive adult patients with acute herpes zoster were tested for the presence of varicella-zoster virus (VZV) antibodies. All acute sera were tested subsequently by real-time polymerase chain reaction (PCR) for the presence of VZV DNA. In addition, convalescent sera of patients who tested initially positive for VZV DNA underwent PCR analysis.
Results: VZV IgM antibodies were found by enzyme immunoassay (EIA) in 5 acute (9%) and 20 convalescent (38%) zoster sera. VZV DNA was detected by PCR in 21 (40%) acute zoster sera and was no longer detectable in the convalescent samples. A seroconversion or a fourfold or greater titre increase was found by complement fixation (CF) test in 41 (77%), by IgG indirect fluorescent antibody assay (IgG IFA) in 43 (81%) and by CF and IgG IFA combined in 45 of 53 (85%) paired zoster sera. The combination of all serological methods detected 51 (96%) and PCR combined with serology identified 52 (98%) of 53 patients.
Conclusions: Optimal laboratory sensitivity in the diagnosis of herpes zoster from serum can be achieved by the combination of PCR and serology of paired serum samples. Serological methods alone are of limited value for early diagnosis of zoster when therapy can be initiated, because CF and IgG IFA need convalescent serum and IgM test sensitivity is insufficient. Early diagnosis of VZV reactivation is possible from serum by PCR in the first days of illness and test sensitivity needs further improvement. The findings highlight the need for future studies into the usefulness of PCR and serology in atypical cases of VZV reactivation.