What is the window period for detecting a primary herpes simplex virus infection and when should PCR or type‑specific serology be performed?

HSV Window Period and Testing Timing

Antibodies to HSV develop during the first several weeks after infection with a critical 12-week window period, meaning serological testing performed before 12 weeks post-exposure may yield false-negative results and should be repeated after this interval if recent acquisition is suspected. 1, 2, 3

Understanding the Window Period

The window period represents the time between HSV infection and detectable antibody development:

• Antibodies typically develop within several weeks after primary infection but can take up to 12 weeks to reach detectable levels 1, 3
• Testing performed within 12 weeks of potential exposure may produce false-negative results during this serological window period 2, 3
• The incubation period for symptomatic disease is 2-10 days (up to 4 weeks), which is distinct from the antibody window period 1

When to Perform PCR Testing

PCR/NAAT should be performed when active lesions are present, as this is the optimal time for viral detection:

• Collect specimens from active vesicles or ulcer bases during symptomatic episodes for maximum sensitivity (>90% for FDA-approved assays) 4, 5
• PCR has 11-71% superior sensitivity compared to viral culture and is now considered the gold standard for diagnosing genital herpes with active lesions 4, 6
• Never perform PCR/NAAT in the absence of active lesions, as HSV shedding is intermittent and swabs without lesions are insensitive and unreliable 3, 4

When to Perform Type-Specific Serology

Type-specific serology using glycoprotein G-based assays should be performed in specific clinical scenarios:

Appropriate Testing Scenarios:

• Pregnant women at risk of acquiring HSV infection close to delivery 1, 2, 3
• Men who have sex with men 1, 2, 3
• People who are HIV-positive 1, 2, 3
• Sexual partners of individuals with known genital herpes 3
• Patients presenting without active lesions but with history suggestive of genital herpes 1, 4

Testing Algorithm for Serology:

• Order type-specific HSV-2 IgG using glycoprotein G-based EIA or CLIA as initial test 2
• If testing within 12 weeks of potential exposure and result is negative, repeat testing after 12 weeks to account for the window period 2, 3
• For low-positive results (index value 1.1-2.9), confirm with a second assay using different glycoprotein G antigen, as these have only 39.8% specificity 2, 4

Critical Pitfalls to Avoid

Testing too early is the most common error:

• A negative serological test within 12 weeks of exposure represents a true false-negative during the window period, not absence of infection 2, 3
• Ordering serology when active lesions are present misses the opportunity for definitive PCR diagnosis, which provides both detection and typing 2
• Reporting low-positive results (index 1.1-2.9) without confirmation leads to false-positive diagnoses with 60% false-positive rate 2, 3
• HSV-1 serology has only 70.2% sensitivity, resulting in frequent false-negatives and should not be relied upon for diagnosis 2, 3

Screening Recommendations

Widespread screening for HSV antibodies in asymptomatic general populations is not recommended:

• The U.S. Preventive Services Task Force gives a Grade D recommendation against routine screening in asymptomatic adolescents and adults 3
• Screening should be limited to high-risk groups as outlined above 1, 2, 3