On campus dormitories as viral transmission sinks: Phylodynamic insights into student housing networks during the COVID-19 pandemic

University student housing environments are often viewed as hotspots for infectious disease transmission due to their high-density living conditions and high frequency of interpersonal interactions. During the COVID-19 pandemic, concerns arose that on campus dormitories could serve as amplifiers of viral spread, seeding outbreaks into surrounding off campus student residences. However, whether on campus housing acts as a primary driver of transmission or as a recipient of infections introduced from the broader off campus community remains unresolved. Here, we analyzed 1,431 SARS-CoV-2 genomes collected from students residing on and off campus at the University of North Carolina at Charlotte (UNCC) between September 2020 and May 2022. Sequencing was conducted using an amplicon based whole genome sequencing approach on the Oxford Nanopore PromethION platform. Using Bayesian phylodynamic and ancestral state reconstruction approaches, we traced viral transmission pathways to determine the directionality of spread between residential settings. Our results indicate that transmission from off campus housing consistently seeded on campus dormitory outbreaks. In contrast, viral movement from on campus to off campus housing was minimal. These patterns persisted across all major pandemic waves, regardless of shifting mitigation strategies, and suggest that on campus residences acted as transmission sinks rather than sources of broader student outbreaks. These findings raise the possibility that on campus residences may be more vulnerable than often considered, functioning as epidemiological 'islands' that primarily receive infections from off campus sources.