What is the rate of neonatal Herpes Simplex Virus (HSV) transmission during vaginal delivery with non-primary active lesions?

Rate of Neonatal HSV Transmission During Vaginal Delivery with Non-Primary Active Lesions

The rate of neonatal HSV transmission during vaginal delivery with non-primary active lesions (recurrent infection) is approximately 0-5% for women shedding HSV caused by reactivated infection at the time of delivery. 1

Understanding HSV Transmission Risk Based on Infection Type

The risk of neonatal HSV transmission varies significantly based on the type of maternal infection:

1. Primary HSV infection (first episode, no prior antibodies):

   • Transmission rate: 30-50% 1
   • Highest risk scenario, especially in third trimester

2. Non-primary first episode (first clinical episode but with prior antibodies to a different HSV type):

   • Intermediate risk

3. Recurrent HSV infection (reactivation):

   • Transmission rate: 0-5% 1
   • Lower risk due to maternal antibodies providing partial protection to the neonate

Risk Factors That Increase Transmission Probability

Even with recurrent lesions, certain factors increase the risk of transmission:

• Presence of active genital lesions at delivery
• Viral shedding at the time of delivery (may be asymptomatic)
• Prolonged rupture of membranes (>6 hours) 1
• Invasive monitoring procedures (e.g., fetal scalp electrodes) 1
• Prematurity of the infant

Prevention Strategies for Mothers with Active Lesions

When active non-primary lesions are present during labor:

• Cesarean delivery substantially lowers the risk for transmission 1
• Cesarean section should be performed before rupture of membranes when possible
• If membranes have been ruptured >4-6 hours, the protective effect of cesarean delivery is reduced but still beneficial

Important Clinical Considerations

1. Asymptomatic shedding is common:

   • Among women without HIV, approximately 2-3% will be shedding HSV on the day of delivery 1
   • This rate increases to approximately 10% in HIV-coinfected women 1

2. Maternal antibody status significantly affects transmission risk and severity of neonatal disease 1

3. Clinical manifestations of neonatal HSV infection include:

   • Disseminated multiorgan disease (25% of cases)
   • Localized CNS disease (35% of cases)
   • Localized skin, eye, and mouth disease (40% of cases) 1

Pitfalls to Avoid

• Do not rely solely on visible lesions to determine risk - asymptomatic viral shedding is common and can still lead to transmission
• Do not assume previous cesarean delivery history protects against current transmission - each delivery must be evaluated independently
• Do not delay antiviral therapy for neonates with suspected HSV exposure - early treatment is critical for improving outcomes
• Do not underestimate recurrent lesions - while the risk is lower than primary infection, transmission can still occur (0-5%)

The 0-5% transmission rate with recurrent lesions represents a significant risk given the potentially devastating consequences of neonatal HSV infection, including long-term neurological sequelae and mortality.