How can neonatal herpes simplex virus infection be clinically recognized in infants under 12 weeks, including signs, lesions, and maternal risk factors?

Clinical Recognition of Herpes Simplex Virus in Infants

Neonatal HSV infection presents most commonly at 8-11 days of age with three distinct patterns: disseminated disease (25%), CNS disease (35%), or skin-eye-mouth disease (40%), but critically, vesicular lesions are absent in 40% of CNS/disseminated cases, making clinical recognition challenging and requiring a high index of suspicion in any unwell neonate. 1

Clinical Presentation by Disease Type

Disseminated Disease (25% of cases)

• Timing: Typically appears at 6-9 days of age 1
• Key features:
  • 65.8% are afebrile 2
  • 73.7% have no skin lesions 2
  • Non-specific signs of sepsis predominate
  • Encephalitis occurs in 60-75% of these infants 1
  • Median CRP only 4 mg/L (IQR 1-14) 2
  • Involves liver, adrenals, lung, kidney, spleen, brain 1
  • Highest mortality: 65.8% 2

CNS Disease (35% of cases)

• Timing: Median onset at 14 days 1
• Presentation: Seizures, lethargy, irritability, poor feeding
• Critical finding: Only 60% have vesicular rash 1
• CSF pleocytosis typically present 3

Skin-Eye-Mouth Disease (40% of cases)

• Timing: Appears at 8-10 days 1
• Presentation: 80% have vesicular rash 1
• Lesions on skin, conjunctiva, or oral mucosa
• Best prognosis but can progress without treatment

High-Risk Clinical Scenarios

16% of infants present without classic signs (no seizure, vesicular rash, or critical illness) 3. These infants share specific characteristics:

• Age ≤14 days 3
• CSF pleocytosis present 3
• Most develop classic signs within 24 hours 3

Maternal Risk Factors

81.4% of infected infants are born to mothers without known/disclosed genital herpes history 2, making maternal history unreliable for excluding HSV.

Highest Risk Maternal Factors:

• Primary maternal HSV infection near delivery: 30-50% transmission risk 4, 1
• Maternal HSV-2 seropositivity with HIV coinfection: 10% cervical shedding at delivery 1
• Recurrent maternal HSV: only 0-5% transmission risk 4, 1
• Prolonged rupture of membranes >6 hours 1
• Vaginal delivery with active lesions 5, 1

Preterm Infants at Higher Risk:

• 34.5% of HSV cases occur in premature infants 2
• Preterm infants with maternal HSV history have 2.51-fold increased odds 6
• Prolonged rupture of membranes: 2.64-fold increased odds 6
• Leukopenia: 3.65-fold increased odds 6
• Thrombocytopenia: 2.25-fold increased odds 6

Key Laboratory Findings

Standard infection markers are often normal or minimally elevated:

• Median CRP: 4 mg/L 2
• Leukopenia and thrombocytopenia more predictive than elevated markers 6

Critical Diagnostic Algorithm

Test for HSV in any infant <90 days with:

1. Any vesicular lesions (regardless of other symptoms)
2. Seizures in first 6 weeks of life
3. Septic appearance with normal bacterial cultures
4. Age ≤14 days with CSF pleocytosis 3
5. Fever + irritability + oral ulcers (gingivostomatitis)
6. Maternal history of genital herpes during pregnancy 5
7. Preterm infant with prolonged rupture of membranes + thrombocytopenia 6

Diagnostic Testing

For suspected neonatal HSV, obtain cultures from: 1

• Blood
• Skin vesicles (if present)
• Mouth/nasopharynx
• Eyes
• Urine
• Stool/rectum
• CSF for HSV PCR (gold standard for CNS disease) 1

Positive cultures from mucosal sites >48 hours after birth indicate viral replication rather than contamination 1.

Common Pitfalls

1. Waiting for vesicular lesions: 40% of CNS/disseminated cases never develop skin lesions 1, 2
2. Relying on fever: 65.8% of disseminated cases are afebrile 2
3. Trusting normal inflammatory markers: CRP often remains low 2
4. Excluding HSV based on negative maternal history: 81.4% of mothers had no known history 2
5. Delaying empiric treatment: 56.7% of infants started acyclovir >24 hours after symptom onset, contributing to poor outcomes 2

Outcomes Without Recognition

• Overall mortality: 23.9% 2
• Disseminated disease mortality: 65.8% 2
• Neurodevelopmental impairment at 24 months: 29.3% overall (45% CNS, 25% disseminated, 11.8% SEM) 2

The evidence strongly supports maintaining a low threshold for empirically testing and treating HSV in any unwell neonate, particularly those ≤14 days of age, given the devastating consequences of delayed recognition and the frequent absence of classic clinical features. 2, 7, 8