A Vesicle on Day 9: When a Well-Appearing Neonate Is Not Reassuring
A 9-day-old girl, born at term after an uncomplicated vaginal delivery, is brought for a 24-hour history of poor feeding and a 2-cm cluster of vesicles on the left scalp. She is afebrile, alert, and has a normal neurologic examination. The mother has no history of genital herpes, and no lesions were noted at delivery. The emergency department resident obtains a surface swab for HSV PCR, sends blood for HSV PCR and liver enzymes, and plans to discharge the infant on oral acyclovir after the swab result returns. The parents are reluctant to agree to a lumbar puncture because the baby 'looks well.'
1. The resident's plan is unsafe. What evaluation and initial therapy does this infant need, and why is oral acyclovir inappropriate?
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Any neonate with a vesicular rash must be evaluated for disseminated and CNS HSV, even if well-appearing and afebrile. The evaluation includes swabs of the vesicles, conjunctivae, mouth, and nasopharynx for HSV PCR; blood HSV PCR; liver enzymes; CBC; and CSF PCR with cell count and protein. A lumbar puncture is required because CNS involvement can occur without neurologic signs and alters duration.
Start empiric IV acyclovir 60 mg/kg/day divided every 8 hours (20 mg/kg/dose) immediately after specimens are collected; do not wait for results and do not use oral acyclovir, which has unreliable exposure in neonates and is inadequate for CNS or disseminated disease. The absence of maternal genital herpes and a normal examination do not exclude HSV; most neonatal HSV is perinatally acquired, and maternal history is often absent. Use contact precautions and monitor renal function and neutrophils.
2. The CSF PCR returns negative at 36 hours. How do you interpret that, and does it change duration?
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A negative CSF PCR at 36 hours does not exclude CNS HSV, especially if the specimen was obtained early or after a traumatic tap. If surface or blood PCR is positive and the infant has vesicles, the diagnosis is at least skin-eye-mouth disease; treat for 10–14 days if CNS and disseminated disease are excluded. If CNS disease is possible-seizures, lethargy, CSF pleocytosis, or positive blood PCR-treat for 21 days and repeat CSF PCR near the end; a negative repeat supports stopping.
In this well-appearing infant with a normal CSF and negative CSF PCR, the minimum is IV acyclovir for 10–14 days for SEM disease, with close neurologic monitoring. Do not shorten to a few days based on one negative PCR; the risk of relapse and late neurologic injury is the reason for prolonged therapy.
3. What follow-up and counseling are needed at discharge?
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At discharge, complete the acyclovir course, ensure renal function and neutrophil counts are monitored, and teach the family to return for lethargy, seizures, poor feeding, or new vesicles. Ophthalmologic examination before discharge is needed if there was eye involvement; developmental follow-up is appropriate after CNS or disseminated disease. Counsel that HSV can reactivate and that future febrile illness or skin lesions should prompt evaluation.
If the infant had SEM disease only, the prognosis is good but not zero; if CNS disease is later confirmed, longer therapy and neurology follow-up are required. Review infection prevention at home-hand hygiene and avoiding kissing the infant with active herpes labialis-because susceptible neonates remain at risk.