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

## TL;DR

This study uses a mathematical model to show that HSV-1 spreads more among children of similar ages but more broadly among adults in the US.

## Contribution

The study introduces a novel mathematical modeling approach to quantify age-dependent assortativeness in HSV-1 oral transmission.

## Key findings

- Children show strong age-based assortativity in HSV-1 transmission (assortativeness of 0.87).
- Adults exhibit weak age-based assortativity in HSV-1 transmission (assortativeness of 0.04).
- Children primarily acquire HSV-1 from peers, while adults get it from multiple age groups.

## Abstract

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 (US) population.

An age-structured mathematical model was employed to describe HSV-1 transmission dynamics in the US population, incorporating its different modes of transmission. The model was fitted to nationally representative HSV-1 data from the National Health and Nutrition Examination Survey (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).

The model demonstrated robust fits to US 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% credible interval [CrI], .64–.99) for children, indicating strong age-based assortativity, and as 0.04 (95% CrI, .004–.10) for adults, indicating weak age-based assortativity.

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.

Herpes simplex virus type 1 transmission exhibits distinct age-related patterns, characterized by strong age assortativity among children and weak age assortativity among adults. This distinction highlights the critical role of age-specific social networks in shaping transmission dynamics.