Herpes Simplex Testing: Methods, Limitations, and Interpretation

Herpes simplex virus (HSV-1, HSV-2) infection is common and often asymptomatic. Testing strategies depend on clinical context.

Virologic Tests (Active Lesions)

• NAAT (PCR) – Gold standard: Swab lesion base. Sensitivity >95%, specific, types HSV-1/2. Preferred over culture.
• Viral culture: Lower sensitivity (50–70%), slower (2–5 days), but allows susceptibility testing. Declining use.
• Direct fluorescent antibody (DFA) / Antigen detection: Rapid, lower sensitivity than NAAT.

Serologic Tests (Asymptomatic / Past Exposure)

• Type-specific IgG (glycoprotein G-based): Detects HSV-1 vs HSV-2 antibodies. IgM is unreliable – do not use.
• Window period: 2–12 weeks (up to 16) post-exposure for seroconversion.
• Interpretation:
  • HSV-2 IgG+ = genital herpes (almost always).
  • HSV-1 IgG+ = oral or genital (increasing genital HSV-1).
  • Both negative = no evidence of past infection (if past window).
• Limitations: Cannot determine site of infection (except HSV-2 ≈ genital), timing of acquisition, or infectiousness. False positives occur at low index values (1.1–3.5) – confirm with second test or Western blot (UW).

Clinical Scenarios

• Symptomatic: NAAT swab lesion. If negative but high suspicion, repeat or serology later.
• Asymptomatic screening: Not routinely recommended (USPSTF Grade D). Consider: partner with HSV, HIV+, MSM, pre-pregnancy counseling.
• Pregnancy: Serology at first visit if partner history. Suppressive acyclovir from 36 wks if HSV-2+.

Counseling Points

• Asymptomatic shedding occurs (10–20% days HSV-2; less HSV-1 genital).
• Condoms reduce transmission ~50%; suppressive antiviral (valacyclovir 500 mg daily) ↓ transmission 48%.
• Neonatal herpes rare but devastating; cesarean if active lesions/prodrome at labor.

Test with purpose. A positive serology without symptoms requires careful counseling about implications.