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Aiding in the rapid diagnosis of herpes simplex virus (HSV) infections, including qualitative detection of HSV DNA in cerebrospinal fluid and other (non-blood) clinical specimens
Qualitative detection of HSV DNA
Herpes simplex virus (HSV) causes various clinical syndromes. Anatomic sites infected include skin, lips, oral cavity, eyes, genital tract, and central nervous system (CNS). Systemic involvement may also occur.
Fresh brain tissue is the definitive specimen for detection of HSV from patients with CNS disease. However, because brain biopsy is an invasive procedure, it is infrequently performed for laboratory diagnosis. Similarly, it is difficult to recover HSV from cerebrospinal fluid (CSF) specimens in culture systems, and the serologic diagnosis of HSV CNS disease has not been informative during early onset disease. HSV PCR detection from CSF is a sensitive and specific alternative for detection of disease involving the CNS, as well as oral, genital, ocular, and other sites.
This is a qualitative assay; results are reported either as negative or positive for herpes simplex virus (HSV) type 1 or HSV type 2. In a small number of cases (eg, <1%), HSV is detected but this assay may not be able to provide a definitive subtype (HSV-1 versus HSV-2). This is due to mutations in the region of the HSV genome that the PCR probes bind to. When this is observed, the report will go out as "Indeterminate", which means that HSV DNA was detected, but the assay was unable to provide a specific subtype.
Detection of HSV DNA in clinical specimens supports the clinical diagnosis of infection due to the virus.
HSV DNA is not detected in cerebrospinal fluid from patients without central nervous system disease caused by this virus.
A negative result does not eliminate the possibility of herpes simplex virus (HSV) infection. HSV DNA may not be detectable in the early acute stages of the central nervous system disease. In addition, in some cases, after initial detection (positive result), HSV DNA may only be present in cerebrospinal fluid (CSF) for 3 to 4 weeks after initial presentation of symptoms. DNA levels may fall to undetectable with time.
Although the reference range is typically "negative" for this assay, this assay may detect viral shedding in asymptomatic individuals. This may be especially relevant when dermal or genital sites are tested, since intermittent shedding without noticeable lesions has been described.(1) CSF DNA is not expected to contain detectable HSV DNA in patients without related disease. This assay is only to be used for patients with a clinical history and symptoms consistent with HSV infection, and must be interpreted in the context of the clinical picture. This test should not be used to screen asymptomatic patients.
Accuracy/Diagnostic Sensitivity and Specificity:
Of 200 specimens processed by both shell vial assay and LightCycler, herpes simplex virus (HSV) was detected in 88 specimens (44%). All 88 positive specimens were detected by LightCycler compared with 69 by the shell vial assay. The 19 discrepant results (LightCycler positive, shell vial assay negative) were resolved as true positive results by using a PCR assay directed to another gene target (thymidine kinase) of the virus.
Of 100 cerebrospinal fluid (CSF) specimens tested by both conventional PCR and LightCycler, HSV was detected in 38 specimens by both techniques. Four specimens were detected only by conventional PCR; however 6 specimens were detected exclusively by LightCycler. Fifty-two specimens were found to be negative for HSV by both techniques.
Supplemental Data (Spiking Studies):
To supplement the above data, approximately 30 negative specimens each of various types were spiked with HSV 1 and HSV 2 plasmid control at the limit of detection (10 copies DNA target/microliter). The spiked specimens were run in a blinded fashion along with approximately 30 negative (nonspiked) specimens each of various specimen types; among the spiked specimen types, the assay was positive in 92% to 100% of the replicates tested. Furthermore, 100% of the nonspiked specimens were negative.
Analytical Sensitivity/Limit of Detection (LoD):
The lower LoD of this assay is 10 DNA target copies per microliter. This was established in anogenital swabs and confirmed in each specimen type accepted for this assay.
No PCR signal was obtained from extracts of 27 bacterial, viral, and fungal isolates that could be found as normal flora in sites normally tested for this organism or that could cause similar symptoms.
Inter-assay and intra-assay precision was 100% and 100%, respectively.
1. Schiffer JT, Corye L: New concepts in understanding genital herpes. Curr Infect Dis Rep Nov 2009;11(6):457-464
2. Espy MJ, Uhl JR, Svien KA: Laboratory diagnosis of herpes simplex virus infections in the clinical laboratory by LightCycler PCR. J Clin Microbiol 2000;38(2):795-799
3. Espy MJ, Ross TK, Teo R: Evaluation of LightCycler PCR for implementation of laboratory diagnosis of herpes simplex virus infections. J Clin Microbiol 2000;38(8):3116-3118
4. Sauerbrei A, Eichhorn U, Hottenrott G, Wutzler P: Virological diagnosis of herpes simplex encephalitis. J Clin Virol 2000;17(1):31-36
5. Mitchell PS, Espy MJ, Smith TF, et al: Laboratory diagnosis of central nervous system infections with herpes simplex virus by PCR performed with cerebrospinal fluid specimens. J Clin Microbiol 1997;35(11):2873-2877
6. Yi-Wei T, Mitchell PS, Espy MJ, et al: Molecular diagnosis of herpes simplex virus infections in the central nervous system. J Clin Microbiol 1999;37(7):2127-2136