Age-Dependent Assortativeness in Herpes Simplex Virus Type 1 Oral Transmission in the United States: A Mathematical Modeling Analysis.

Background: Herpes simplex virus type 1 (HSV-1) is a highly infectious, globally prevalent lifelong infection. Despite advancements in understanding its epidemiology, the assortativeness in the age-dependent transmission patterns remains unclear. This study aimed to estimate the degree of assortativeness in age group mixing for oral-to-oral HSV-1 transmission within the United States (U.S.) population.

Methods: An age-structured mathematical model was employed to describe HSV-1 transmission dynamics in the population, incorporating its different modes of transmission. The model was fitted to nationally representative HSV-1 data from the National Health and Nutrition Examination Surveys (NHANES) spanning 1976-2016 using a Bayesian inference framework. The degree of assortativeness in age group mixing was calibrated on a scale from 0 (no age group bias in close-proximity interactions) to 1 (exclusive mixing within the same age group).

Results: The model demonstrated robust fits to U.S. demographics, age-specific HSV-1 prevalence, and temporal trends in both HSV-1 prevalence and ever-symptomatic HSV-1 genital herpes prevalence. The degree of assortativeness was estimated as 0.87 (95% CI: 0.64-0.99) for children, indicating strong age-based assortativity, and as 0.04 (95% CI: 0.004-0.10) for adults, indicating weak age-based assortativity.

Conclusion: Most HSV-1 infections among children are acquired from peers within their own age group, whereas adults acquire HSV-1 infections from a broad range of age groups.