Epidemiology of Herpes Simplex Virus in Infants Aged 0-42 Days: 2008-2024

Infant herpes simplex virus (HSV) incidence ranges from 1.7 to 13.4 per 100 000 live births, varies by region, and prior to 2019, has been increasing. HSV-1 has surpassed HSV-2 as the predominant subtype. We aimed to report trends in infant HSV disease.

This was a retrospective study of infants aged 0-42 days born between October 1, 2008 to September 30, 2024 with HSV disease. Demographics, clinical symptoms, type of HSV disease, and subtype of HSV were captured. Trends of HSV disease and subtype were reported.

In our 16-year cohort of 632 979 infants, we identified 62 cases of HSV disease, with a cumulative incidence of 9.8 (95% CI 7.6-12.5) per 100 000 births. The cumulative incidence of skin, eye, and/or mouth (SEM), disseminated (DIS), and central nervous system (CNS) disease were 5.4 (95% CI 3.7-7.5), 2.8 (95% CI 1.7-4.5), and 1.6 (95% CI 0.8-2.9) per 100 000 births, respectively. SEM and CNS disease incidence remained stable during the study period. However, there was a statistically significant change in the incidence of DIS disease between 2008-2021 and 2021-2024 with a rise in DIS disease of 4.5 per 100 000 births per year from 2021 to 2024. HSV-1 disease occurred in 61% and HSV subtype distribution was stable over time.

SEM disease and HSV-1 were predominant throughout the study period. Incidence of DIS disease increased significantly after the COVID-19 pandemic, likely reflecting changing sexual practices during the pandemic and a population vulnerable to primary HSV-1 genital lesions.