Introduction
The prevalence of genital herpes simplex virus type 2 (HSV-2) infection is greater than 20% among adults in the United States.[1] According to the recent National Health and Nutrition Examination Survey, (NHANES III)[2] the prevalence of seropositivity among race and gender is 20% in white women, 15% in white men, 55% in black women, and 35% in black men. Eighty percent of HSV-2 infected persons have unrecognized genital herpes, 20% have no symptoms, and 60% have atypical symptoms.
Clinical Approach
Identified risk factors for acquiring genital herpes infection include larger number of lifetime sexual partners, history of sexually transmitted infections, increasing age, and sexually transmitted disease clinic attendees.[3,4] Including a questionnaire regarding risk factors as part of the evaluation of the patients not only serves its purpose of identifying those who are at risk of contracting the infection, but would help increase the positive predictive value of the specific serological tests if they were to be necessary (see below).
The typical clinical presentation of genital herpes usually includes classic vesicular lesions, bilateral genital ulcers, tender inguinal lymphadenopathy, and constitutional signs. Two different scenarios may occur. The first, known as primary genital herpes, occurs when the patient has no antibodies to HSV-1 or HSV-2. It is expected to present as a severe and prolonged episode (up to 21 days) of multiple coalescent vesicular-ulcerative lesions with systemic illness, in which common symptoms are headache, photophobia, and neck stiffness. In the presence of HSV-1 antibodies, the first episode of HSV-2 infection is usually milder. The second scenario constitutes recurrent episodes that typically last 7-10 days, and symptoms are less severe than for the first episode. Local prodromal symptoms (e.g., itching, tingling, pain) may "announce" the next episode hours or days before the lesions develop. While primary HSV-1 genital infections are clinically indistinguishable from primary episodes caused by HSV-2, recurrent episodes are more likely with HSV-2 infection, as HSV-2 reactivates more frequently than HSV-1.[5]
A great number of cases may present in an atypical way with skin splits, fissures, minor abrasions, erythema, and pain. Primary genital herpes may appear benign, with no signs or symptoms recognized by the patients or their health care providers as being due to genital HSV infection.[6] Rarely, recurrent infection may present with systemic symptoms such as fever, chills, and myalgias.[7]
Clinician detailed interviews are not effective in identifying the infection[8] and a diagnosis based solely on clinical presentation has a poor sensitivity. The predictive value of a genital herpes diagnosis based on clinical signs alone is only about 40%.[9] Therefore, laboratory methods of diagnosis are an inherent and essential step in the diagnosis of genital herpes.
Direct Methods
These methods are called direct because the sample is taken from the lesion at or near a genital site or from genital secretions. Samples should be taken early in the genital herpes outbreak and no later than the vesicular stage. Sampling should be multifocal. Sensitivity of these tests is lower in individuals with recurrent lesions than those with first episodes.[10]
Cytologic Diagnosis. A Tzanck smear is obtained when scrapes of herpetic lesions are followed by Wright-Giemsa staining. It is simple, rapid, and inexpensive, but has a high rate of false negatives and does not distinguish between HSV-1 and HSV-2. The Tzanck test may be conveniently considered as a complement to the initial clinical evaluation of the patient with symptomatic infection because its result will provide additional evidence of the herpetic nature of the lesion.
Viral Culture. Currently, viral culture is the principal means of diagnosing genital herpes, constituting the first choice for patients presenting with genital lesions. Specificity is 100% for both HSV-1 and HSV-2, but up to 50%-60% of cultures are negative. A sensitivity of 75% for the first episode and of 50% for recurrences has been reported.[10,11] Results are available in 2-3 days. Despite the fact that the sensitivity is low and dependent on the stage of the genital herpes episode at which the swab is taken, this test should always be pursued because of its specificity for both HSV-1 and HSV-2; along with polymerase chain reaction (PCR), it is the only test which directly identifies the nature of the herpetic infection (HSV-1 vs. HSV-2) within the lesion itself.
PCR for HSV-1 and -2. The PCR method has a 100% specificity and higher sensitivity than viral culture.[2] Financial justification and benefits of using HSV PCR for genital herpes diagnosis instead of viral culture remains to be established. Viral DNA detection by PCR is still very much a research tool.
Indirect (Serologic) Methods
Western Blot Assay. Considered the gold standard for the detection of antibodies to HSV, this test uses denatured, separated proteins fixed on paper strips (blots) of either HSV-1 or HSV-2. This method is accurate in detecting type-specific antibody responses and it identifies seroconversion more quickly because of the greater numbers of antigens available. It can also detect early seroconversion to HSV-2 in patients with prior HSV-1 infection.[12] Its specificity and sensitivity are nearly 100%[13]; however, it is expensive, requires 2-5 days for screening and confirmation by preadsorption, is not easy to use, and is not available in many laboratories. University of Washington (Seattle, USA) Western blot (UW WB) is available as a gold standard HSV type-specific test for regional or reference testing.
Enzyme Immunoassays. These tests have not been used in recent years due to their lack of specificity (HSV-1 and HSV-2). They have been commercially available for some time and are based on crude antigen preparations, which are inaccurate and misleading because of extensive cross-reactivity between HSV-1 and HSV-2. A list of these not recommended tests is available.[14]
Glycoprotein G-Based Tests (Type-Specific Antibody Tests). The new generation of enzyme immunoassays are called the glycoprotein G (gG)-based type-specific serologic assays for HSV-1 and HSV-2. Glycoprotein G is an envelope protein from the virion and contains predominantly type-specific epitopes, unique to either HSV-1 or HSV-2. Antibodies to gG1 (elicited by HSV-1) or to gG2 (elicited by HSV-2) are therefore valuable markers of infection with these viruses. Until March of 2001, three companies, Meridian Bioscience Inc., MRL Diagnostics (now called "Focus Technologies"), and Diagnology, had received approval from the US Food and Drug Administration for a total of six gG based diagnostic tests kits: two for HSV-1, three for HSV-2, and one that combines both in one kit.[14]
Food and Drug Administration Licensed Kits
POCkit HSV-2 Rapid Test (Diagnology, Belfast, Northern Ireland). This test uses capillary blood from a fingerstick or serum and provides rapid results (6 minutes). It is considered moderately complex and can be performed in clinics or offices that are certified under the Clinical Laboratories Information Amendment (CLIA). When compared with Western blot analysis its sensitivity was 96% and specificity was 97%.[15] This test is able to detect HSV-2 antibodies in 2 weeks, with a response time that varies from 3-102 days (seroconversion detected within 4 weeks in 80% of patients with HSV-2 episodes). It detects human light chain as well as human heavy chain IgG. As a result, early determination of HSV-2 IgM antibody is possible, making this test valuable for the diagnosis of patients with a first episode of HSV-2 infection.[8] This test is approved only for use in adult men and women. Another test version of the test, but less complex, is in trials as a CLIA-waived device. Its name is POCkit-HSV-2 holos. This test is supposed to be used in clinics and office settings that do not have CLIA accreditation.[16]
HerpeSelect (Focus Technologies/MRL Diagnostics, Cypress, CA). This brand includes two enzyme-linked immunosorbent assays (ELISA) and one immunoblot test. All three tests are approved for use in adults and in pregnant women, and they are marketed as kits under the brand name HerpeSelect. HerpeSelect HSV-1 ELISA and HSV-2 ELISA are separate kits and are sold individually. HSV-2 ELISA has a sensitivity of 96%-100% and a specificity of 92%-95% when compared with UW WB.[17] HSV-1 ELISA had 91%-96% sensitivity and 96%-97% specificity in these groups.[17,18] The other HerpeSelect test is an immunoblot that includes both gG1 and gG2. The test has a 97%-100% sensitivity for HSV-2 immunoblot, and 94%-98% specificity in clinical trials. For HSV-1 immunoblot a sensitivity of 99%-100% and a specificity of 92%-95% have been reported.[16]
Premier Type (Gull Laboratories/Meridian Diagnostics). The Premier Type tests consisted of ELISA kits for gG1 and gG2, but these tests are no longer available. When compared with Western blot analysis, the sensitivity for HSV-1 was 81%-90% and the specificity 96%. For HSV-2, sensitivity was 98% and specificity was 97%.[19]
Interpretation of the Type-Specific Antibody Tests
Positive predictive values depend on the performance of the test in both high- and low-incidence populations.[2] Despite the progress that gG2-based ELISAs bring, determination of the individual serostatus may require confirmation in a second assay, such as immunoblotting, or even a combination of sequential use of two screening ELISAs and retesting of sera with equivocal results by immunoblotting.[20] Evaluation of confirmatory strategies for detection of type-specific antibodies against HSV-2 showed an increase in the specificity of HSV-2 specific serology.[20]
As in any test based on antibodies to only one protein, gG-based test results are vulnerable to variations in the titers and timing of the antibody responses to that protein.[21] Antibodies to gG arise relatively late, first appearing 2-3 months after the infection in 60%-70% of newly diagnosed patients.
Positive Test Result. Nearly all patients with positive specific serology for HSV-2 have genital herpes, although rare HSV-2 infection limited to the oral mucosa may occur.[10] Oral HSV-2 infection in the absence of genital HSV-2 infection is thought to be rare. Specificity is high for the type-specific test already mentioned; however, the positive predictive value of these tests decreases as the prevalence of infection in the population decreases.[2,16] Therefore, for patients without a history of risk factors, or in pregnant women, confirmation of a positive test is advisable. Testing a second sample later or requesting a different gG-based test on the positive sample is advisable.[16,13,22] Confirmation can be done using UW WB.[23,24,25] HerpeSelect immunoblot has been used with success to confirm HerpeSelect ELISA results in a low prevalence population.[26]
Negative Test Result. Negative results can mean the patient does not have the infection, has not made antibodies yet, or has made antibodies that do not react in the given test.[16] A low-risk patient with a negative test is likely to be uninfected, and therefore susceptible to infection. If a patient is symptomatic or has risk factors, a repeat test should be performed. The median time to seroconversion of the test in use should be considered. HerpeSelect ELISA detects seroconversion at a median of 3 weeks. POCkit has a median time to seroconversion of 2 weeks.[15]
Indications to Test
Symptomatic Patients. Patients in whom there is a clinical suspicion of genital herpes infection, and direct methods of diagnosis have failed to show a postive result, can benefit from having type-specific antibody testing for HSV-2 (Figure 1). A positive HSV-2 serologic test does not exclude other causes of a genital eruption, but it supports a diagnosis of infection. Conversely, a negative serology may be useful to exclude genital herpes. If a patient has strong clinical evidence of genital herpes and repeated specific serology for HSV-2 is negative, then a HSV-1 specific serology may be recommended. If it is positive it may be possible that the genital lesion is caused in that patient by HSV-1. Unfortunately, the serology does not differentiate between oral and genital infection.
Suggested algrorithm for the diagnosis of symptomatic genital herpes infection HSV-1/2=herpes simplex virus type 1/type 2.
Pregnant Women. Neonatal herpes is most common when the mother develops primary infection late in pregnancy.[6] Therefore, establishing the susceptibility of the mother to acquire genital herpes infection during the third trimester may be recommended.[7,21]
Monogamous Couples in Discordant Relationship. If a couple is seeking ways to minimize transmission, a reliable blood test may show if they are indeed discordant given that many apparently HSV-negative people are infected. If serology confirms they are discordant, the frequency of transmission, asymptomatic shedding, and suppressive therapy can be discussed.
STD Clinic Attendees and Individuals at Risk of Acquiring HIV Infection. This population has high risk factors for genital herpes infection. Patients should be tested after informed consent is obtained. HSV genital ulcer disease is implicated in the risk of acquiring human immunodeficiency virus (HIV) infection.
© 2003 Le Jacq Communications, Inc.
Cite this: Genital Herpes Infection: Beyond a Clinical Diagnosis - Medscape - Mar 01, 2003.
