Herpes simplex direct detection of genital lesions

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Associate Editor-In-Chief: Lakshmi Gopalakrishnan, M.B.B.S.

Overview

The confirmation and characterisation of the infection and its type, by direct detection of herpes simplex virus (HSV) in genital lesions, are essential for diagnosis, prognosis, counselling, and management.

• Isolation of HSV in cell culture is the preferred virologic test for patients who seek medical treatment for genital ulcers or other mucocutaneous lesions. However, the sensitivity of culture is low, especially for recurrent lesions, and declines rapidly as lesions begin to heal.

• PCR assays for HSV-DNA are more sensitive and have been used instead of viral culture; however, PCR tests are not FDA-cleared for testing of genital specimens. PCR is the test of choice for detecting HSV in spinal fluid for diagnosis of HSV-infection of the central nervous system.

• In all patients with newly diagnosed genital herpes, viral culture isolates should be typed to differentiate between HSV-1 and HSV-2. Lack of HSV detection (by culture or PCR) does not indicate a lack of HSV infection, as viral shedding is intermittent.

• The use of cytologic detection of cellular changes of HSV infection is an insensitive and nonspecific method of diagnosis, both for genital lesions (by Tzanck preparation) and for cervical Pap smears, and should not be relied upon.

Recommendations

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Methods should be used that directly demonstrate HSV in swabs or scrapings from a lesion. Cytological examination (Tzanck and Papanicolaou smears) has modest diagnostic specificity and sensitivity and should not be relied upon for diagnosis. HSV isolation in cell culture is the diagnostic gold standard and the current routine diagnostic method. Isolates can be typed and tested for antiviral susceptibility. Virus culture is slow, labour-intensive and expensive. Specificity is virtually 100%, but levels of virus shedding, quality of specimens, and transport conditions influence sensitivity. First-episode ulcers more often yield the virus than recurrent lesions (82% versus 43%). Average sensitivity is 52% to 93% for vesicles, 41% to 72% for ulcers and 19% to 27% for crusted lesions. Delayed sample processing and lack of specimen refrigeration after collection and during transport significantly reduce the yield of virus culture. HSV DNA detection by polymerase chain reaction (PCR) increases HSV detection rates by 11 to 71% compared with virus culture. HSV PCR is widely available for testing of cerebrospinal fluid in patients with neurological disease. There have been at least 14 large studies comparing virus culture with PCR for the detection of HSV in muco-cutaneous swabs, together comprising data from over 3,500 patients. These studies demonstrated that the relative sensitivity of virus culture averaged 70% and ranged between 25% and 89%. PCR should be implemented, after local validation, as the preferred diagnostic method for genital herpes. Unlike virus culture, PCR-based methods do not rely on virus growth and may allow less stringent conditions for sample storage and transport. Real-time PCR assays allow detection and typing of HSV in a single reaction tube, with faster turn-around-times (potentially 2 hours) and lower risk of contamination than traditional PCR assays. Viral antigen can be detected by direct immunofluorescence assay (IFA) using fluorescein-labelled monoclonal antibodies on smears, or by enzyme immunoassay (EIA) on swabs. IFA shows lower sensitivity (74%) and specificity (85%) than virus culture and cannot be recommended. Commercially available EIAs (e.g., HerpChek, PerkinElmer, Belgium) show ≥ 95% specificity and 62% to 100% sensitivity relative to virus culture. Sensitivity may be higher than virus culture for typical presentations and late specimens, but lower for cervical or urethral swabs and recurrent episodes. HerpChek does not differentiate between HSV types.

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Source

National Guidelines