Neonatal Herpes: The 24th-Hour Workup

Christopher J. Chiu, MD; Justin L. Berk, MD, MPH, MBA


July 30, 2021

Christopher J. Chiu, MD: Hello. We are The Cribsiders. On our pediatric medicine podcast, we interview leading experts in the field to bring you clinical pearls, practice-changing knowledge, and answers to lingering questions about core topics in pediatric medicine. Today we're going to talk about neonatal herpes simplex virus (HSV).

Justin L. Berk, MD, MPH, MBA: We talked about neonatal HSV with Dr Christopher Golden, neonatologist and associate professor of pediatrics at Johns Hopkins University School of Medicine.

Chiu: Neonates who are exposed to HSV in the first 30 days of life are at very high risk of developing infection. But the scariest thing about this is that they can present up to 6 weeks of age. How do they get infected? We learned that 85% of these infections arise from exposure during delivery. Only 10% arise from postnatal exposure, like being kissed or touched by someone with a cold sore or herpetic whitlow.

Berk: It was a big teaching point for me that the majority of these exposures are not from women who have recurrent infections. In fact, the increased likelihood of vertical transmission occurs with mothers who have active primary infections. If the mother has active lesions anywhere, regardless of whether it's primary or recurrent, that can still clearly cause vertical transmission. You can have some asymptomatic shedding at delivery. But it's mainly the new HIV infections (occurring during the third trimester) that can cause problems. The risk is even higher if there is any disruption of the neonate's cutaneous barrier (eg, use of a fetal scalp electrode).

C-sections have actually been demonstrated to decrease the risk because there's less exposure to the vaginal mucosa, but this isn't 100% effective. There's great guidance in the 2018 Red Book, as Dr Gordon mentioned, to help monitor and treat exposed infants.

Because the risk for vertical transmission is so high in primary infections (40%-60%) and lower in recurrent infections (less than 5%), management can vary (Figure).

Management of asymptomatic neonates exposed to active genital lesions. Courtesy of The Cribsiders. Download PDF

Known prior maternal genital HSV. With known prior genital HSV in the mother, we can assume recurrent infection. This was a learning point for me. This actually suggests a lower risk for vertical transmission because the mother has had time to develop antibodies and pass them along to the unborn baby.

We pretty much do routine care for asymptomatic babies until the 24th hour of life. At that time, we obtain HSV surface cultures (and/or PCRs) and blood HSV PCR.

No known prior maternal genital HSV. However, if there is no pre-pregnancy history of HSV, this suggests a primary infection during pregnancy, posing a bigger risk for neonatal infection and disease.

In this case, if the infant remains asymptomatic, at 24 hours we'll do a full workup, including HSV surface cultures, blood HSV PCR, CSF for indices, culture, and HSV PCR, and serum ALT. We also start IV acyclovir.

Chiu: Why are we waiting until the baby is 24 hours of age?

Berk: It's a great point. You would think you'd want to start this workup immediately, but during those first 24 hours, you can have a lot of false positives just because of maternal secretions that are still present, and that can really confuse the results. After 24 hours, the vernix is gone, and you are really just sampling the neonate's skin and mucosa without any type of maternal contamination.

Chiu: If you want to hear a little more about neonatal HSV treatment and monitoring, check out our podcast, Neonatal HSV – Plain and Simplex.

You can download the podcast on any podcast player or check out our website.


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