DETECTION OF VZV IN HSV-NEGATIVE CSF SAMPLES AND HSV IN VZV-NEGATIVE CSF SAMPLES BY SimplexaTM VIRAL ENCEPHALITIS ASSAY

Introduction: Herpes simplex virus type-1 (HSV-1) and type-2 (HSV-2), varicella-zoster virus (VZV), and enterovirus (EV) are important viral pathogens that cause CNS infection. Detection of the virus in cerebrospinal fluid (CSF) confirms infection. The most commonly used methods for detecting these pathogens are single-plex PCR assays for the detection of both HSV-1 and -2, VZV, or EV. In this study, we evaluated HSV-negative CSF samples for the presence of VZV and EV, and VZV-negative CSF samples for the presence of HSV-1/-2 and EV using Focus Diagnostics’ Simplexa Viral Encephalitis assay* (Simplexa VE assay).

Methods: De-identified remnant HSV-negative CSF specimens (n = 89) and VZV-negative CSF specimens (n = 40) were randomly collected from the Focus Diagnostics Reference Laboratory in 2006. The Simplexa VE assay was used for detection of HSV-1/-2, VZV, and EV. Specimens were also tested by the Focus Laboratory’s in-house single-plex analyte TaqMan^® assays for HSV-1/-2, VZV, and EV for confirmation. Historical percent positivity data from Focus Diagnostics Reference Laboratory for 2006 were used for comparison.

Results: Of 89 HSV-negative samples, 4 (4.5%) were positive for VZV and 2 (2.2%) were positive for EV. Of 40 VZV-negative samples, 5 (12.5%) were positive for HSV-1/-2 and 1 (2.5%) was positive for EV. Historical data for in-house single-target PCR testing from 2006 showed: 1) of all CSF samples submitted for HSV 1/2 testing, 0.7% were positive for HSV-1 and 2.4% for HSV-2; 2) of all samples submitted for VZV testing, 6.9% were VZV-positive; and 3) of all samples submitted for EV testing, 12.3% were EV-positive.

Conclusion:  A noteworthy percentage of VZV-positives were detected in the in-house HSV-negative CSF samples, and a noteworthy percentage of HSV-1/-2 positives were detected in the in-house VZV-negative CSF samples. EV positive results were also found in both VZV-negative and HSV-negative samples, but at a lower rate. These results suggest that single-analyte testing for HSV or VZV may fail to provide the correct diagnosis. A multiplex-assay approach, such as the Simplexa VE assay, that can detect each of these pathogens, can be a useful tool to aid in making a diagnosis of CNS viral infections.

*The Focus Diagnostics Simplexa^TM Viral Encephalitis assays are for research use only in the USA.