Literature review > Issue 8 > Review on Schmutzhard et al. 

Diagnostic modalities for the detection of herpes viruses have evolved rapidly over the last decade, and PCR has become an acceptable alternative to virus isolation by traditional culture methods due its high specificity and sensitivity. The newer methods of diagnosis have changed the awareness of the epidemiology of the herpes viruses, as the older culture methods were quite specific but only moderately sensitive. Initially, PCR was used only as a research tool, as its use was tedious and expensive, but recent developments have allowed PCR to become more automated and less difficult to perform. Consequently, it can now be used for clinical diagnoses, which is significant, since rapid diagnosis of herpes virus infections can assist in the proper choice of interventions.

Schmutzhard et al. compared two types of PCR with the standard virus isolation techniques for HSV-1, HSV-2, and VZV. Their purpose was to validate the use of a commercially available real-time PCR over the more traditional nested PCR. Samples were collected from 110 consecutive clinical samples from either dermal or genital lesions of patients with suspected mucocutaneous HSV infections and another 110 samples of patients with suspected mucocutaneous VZV infections. Among HSV-1, 24 samples (22%) were positive by virus isolation, with no increase by nested PCR and only 2 additional positives by real-time PCR. For HSV-2, 30 samples (27%) were positive by virus isolation, 41 samples (37%) were positive by nested PCR, and 40 were positive by real-time PCR. In cases with suspected VZV, only 15 samples (14%) were detected by isolation methods, and 51 samples (46%) were detected both by nested PCR and real-time PCR. There were no samples that were positive by isolation only. The authors conclude that nested and real-time PCR were equivalent to each other, and that they demonstrated an increased yield of diagnosis that made either suitable for diagnosis of HSV and VZV in suspected mucocutaneous lesions. This paper is a useful addition to the growing literature that validates the use of real-time PCR for rapid diagnosis of clinical specimens as an essential tool that aids clinicians in the identification and management of these infections.

There were several deficiencies, however. First, the study population was not completely described; it is stated that the samples were consecutive clinical samples from dermal or genital lesions. A breakdown of anatomic locations would have been informative. Second, they report that the two PCR methods are equivalent, but there were 2 samples positive for HSV-1 by real-time PCR that were not detected by nested PCR, and there was one sample positive for HSV-2 by nested PCR but not detected by real-time PCR. Certainly these are small numbers, but with the extreme sensitivity of PCR it would have been instructive to show additional information on whether these where false negatives or false positives, and a brief discussion as to why this had been so. Third, the authors report only a doubling in positive samples overall with their techniques. Prior studies have shown that the differences range from 3-fold to 5-fold between culture and DNA detection methods [1]. Fourth, one of the advantages of real-time PCR is a quantitative report on the DNA detected, and although they mention this as useful, they did not report the quantities obtained in the specimens collected.

References:

1. Wald A, Huang M, Carrell D, Selke S, Corey L. Polymerase chain reaction for detection of herpes simplex virus DNA on mucosal surfaces: comparison with HSV isolation in culture. J Infect Dis 2003;188:1345-51.

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