Genital Herpes Simplex Laboratory diagnosis

Laboratory diagnosis

The sensitivity of all laboratory methods depends on the stage of lesions (sensitivity is higher in vesicular than in ulcerative lesions), on whether the patient has a first or a recurrent episode of the disease (higher in first episodes), and on whether the sample is from an immunosuppressed or an immunocompetent patient (more antigen is found in immunosuppressed patients). It is crucial to document genital herpes simplex infection in pregnant women and cutaneous herpes in newborn infants. Consequently, in these instances suspicious vesicular and eroded lesions should be cultured. In all other forms the clinical presentation is usually so characteristic that an accurate diagnosis can be made by inspection. A number of laboratory procedures are available if confirmation is desired.

Culture.

The most definitive method for diagnosis in patients who present with genital ulcers or other mucocutaneous lesions is viral culture which can distinguish between HSV-1 and HSV-2. The culture must be obtained from active lesions during viral shedding, which, on average, lasts 4 days. 50% of cultures are negative in recurrent lesions. Vesicles and wet erosions give a higher yield than dry erosions or crusts. Vesicles are punctured and the fluid is absorbed into the swab, which is then rubbed vigorously onto the base of the lesion. Cervical samples are taken from the endocervix with the swab. From the viewpoint of cost, the insertion of separate swabs from a number of anatomic sites (cervix, vaginal ulcers, vaginal fissures, anus) into one culture vial is the most efficient way to collect genital samples for viral culture. Specimens are inoculated into transport media. Results may be available in 1 to 7 days.

Cytology and histology

Cytologic detection of cellular changes of herpes virus infection is insensitive and nonspecific, both in genital lesions (Tzanck preparation) and cervical Pap smears, and should not be relied on for diagnosis of HSV infection.

The histologic picture is characteristic but not unique for herpes simplex. Polymerase chain reaction assays for HSV is available in some laboratories and is the test of choice for detecting HSV in spinal fluid for diagnosis of HSV-infection of the central nervous system.