Study protocol for estimating modern US social contact patterns: the ENGAGED study

Abstract Background: Accurately capturing social contact data is essential for developing effective mathematical models to forecast disease trends and evaluate interventions. There are limited population-based data of social contacts in the United States (US) which limits our ability to accurately model infectious disease transmission. Methods: To fill in this gap, we conducted a staggered longitudinal cohort study in metropolitan Atlanta, Georgia, USA. We aimed to characterize contact patterns and examine how they varied by i) participant demographics, ii) seasonality, and iii) self-managed and medically-attended symptoms. Once per month for six months, participants reported individual contacts they can name, individual contacts they cannot name, and contacts that occurred in group settings. We defined individual contacts as a two-way conversation with five or more words in the physical presence of another person or physical skin-to-skin contact, and group contacts as contacts with a group of people with whom participants talked, interacted, or shared space. Participants were enrolled on a rolling basis, and data is collected from November 2024 through April 2026. Data analysis will generate age-specific contact matrices using individual contacts and compare contact rates by symptoms. We will also analyze the number and characteristics (e.g. indoor/outdoor) of each type of contacts. The contact matrices and results will be publicly available for the wider modeling community. Discussion: This study is among the first population-level longitudinal studies of social contact patterns in the US. By capturing behavioral changes during periods of both health and illness, and across seasons, this study will provide insights into the complex dynamics of human behavior relevant to infectious disease transmission in the US.