When should HSV IgG serology be performed after a suspected exposure, and what are the recommended diagnostic and treatment approaches for an active herpes infection?

HSV Diagnostic Testing and Treatment Approach

Perform HSV IgG serology at least 12 weeks after suspected exposure, and always use NAAT/PCR—not serology—to diagnose active lesions. 1

Timing of HSV IgG Serology After Exposure

Wait a minimum of 12 weeks after suspected exposure before ordering HSV serology, as antibodies may not be detectable earlier and will yield false-negative results. 1 Testing before this window is unreliable and should be deferred. 1

Critical Limitations of Serologic Testing

Even when performed at the correct time, HSV serology has significant performance issues that you must communicate to patients:

• HSV-1 IgG sensitivity is only ~70%, meaning approximately 30% of truly infected individuals will test falsely negative. 1, 2
• HSV-2 IgG sensitivity is better at ~92%, but still misses about 8% of true infections. 1, 2
• Never tell a patient that negative serology definitively excludes HSV infection—the false-negative rates are too high. 1

Specificity Problems with HSV-2 Serology

HSV-2 serology has poor specificity at low-positive index values (1.1–2.9), with specificity of only ~40%, meaning more than half of results in this range may be false positives. 1

• Specificity improves to ~79% when index values are ≥3.0, but this remains suboptimal. 1
• Patients with prior HSV-1 infection are particularly prone to false-positive HSV-2 results at low index values due to cross-reactivity. 1
• Consider confirmatory testing (ideally Western blot, though typically limited to research settings) when HSV-2 index values fall between 1.1–2.9. 1
• Recent data show that certain platforms (e.g., DiaSorin) have particularly poor performance, with nearly one in three positive HSV-2 results being false positives. 2

Diagnostic Approach for Active Herpes Infection

When Lesions Are Present

Always obtain HSV NAAT/PCR directly from active genital ulcers or lesions—this is the gold-standard diagnostic method with >90% sensitivity and specificity. 1, 3

• Never use serology to diagnose active lesions; serology only indicates past exposure, not current infection. 1, 4
• The PCR assay must distinguish HSV-1 from HSV-2, as this affects counseling and management. 1
• NAAT/PCR is vastly superior to viral culture, which loses sensitivity as lesions heal. 1
• If only viral culture is available due to cost or laboratory constraints, use it but recognize its limitations and consider follow-up serology at ≥12 weeks if results are negative and suspicion remains high. 1

Avoid These Obsolete Tests

• Do not order direct immunofluorescence assays or Tzanck smears—they lack adequate sensitivity. 1
• Do not order HSV IgM—it is useless for diagnosing genital herpes. 3

When No Lesions Are Present

Do not order molecular testing when no visible lesions are present, as intermittent viral shedding renders the test insensitive. 1

In this scenario, type-specific HSV IgG serology (detecting antibodies to glycoprotein G-1 and G-2 via EIA or CLIA) is the only option, but only if performed ≥12 weeks after exposure and with full awareness of the limitations described above. 1

Specific Indications for Serologic Testing

Order HSV serology in these clinical scenarios:

• Patients with recurrent genital symptoms when active lesions are unavailable for NAAT/PCR. 1
• Sexual partners of individuals known to be HSV-positive. 1
• High-risk groups: persons living with HIV, individuals with multiple sexual partners. 1
• Pregnant women when clinically indicated (though universal screening is not recommended). 1, 3
• Patients with uncertain clinical diagnosis who present without active lesions. 1

Note: The USPSTF recommends against routine population-based serologic screening for HSV in asymptomatic adolescents, adults, and pregnant persons, as harms outweigh benefits. 5

Treatment of Active Infection

First-Line Antiviral Therapy

Initiate antiviral therapy promptly when HSV infection is suspected clinically, even before laboratory confirmation, as early treatment reduces illness duration and prevents complications such as urinary retention, meningism, or severe systemic illness. 6

• Current first-line antivirals target viral DNA polymerase (acyclovir, valacyclovir, famciclovir). 7
• These medications have limited efficacy in preventing recurrences and are susceptible to resistance, particularly in immunocompromised populations. 7
• Foscarnet is reserved for acyclovir-resistant cases but has significant toxicity. 7

Severe or Disseminated Infection

For suspected disseminated HSV with multi-organ involvement (hepatitis, encephalitis, myocarditis), order serum PCR for HSV DNA immediately and start intravenous acyclovir without delay. 8

• Serum PCR is an excellent initial diagnostic modality for systemic HSV infection. 8
• Maintain a low threshold for suspecting HSV in patients on corticosteroids or with other immunosuppressive factors. 8
• For CNS manifestations, the Simplexa HSV 1 & 2 Direct is currently the only FDA-approved device for use on cerebrospinal fluid. 4

Pregnancy-Specific Considerations

In pregnant women with genital lesions and no prior history of genital herpes, perform both PCR and type-specific HSV IgG to distinguish true primary infection from non-primary first episode versus recurrence, as this distinction affects delivery planning. 3

• Cesarean delivery reduces neonatal transmission risk when genital lesions or prodromal symptoms are present at delivery. 5
• If a pregnant woman has a history of genital herpes but no current lesions, do not perform genital sampling or serology. 3