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SARS-CoV-2 transmission is largely driven by heterogeneous dynamics at a local scale, leaving local health departments to design interventions with limited information. We analyzed SARS-CoV-2 genomes sampled between February 2020 and March 2022 jointly with epidemiological and cell phone mobility data to investigate fine scale spatiotemporal SARS-CoV-2 transmission dynamics in King County, Washington, a diverse, metropolitan US county. We applied an approximate structured coalescent approach to model transmission within and between North King County and South King County alongside the rate of outside introductions into the county. Our phylodynamic analyses reveal that following stay-at-home orders, the epidemic trajectories of North and South King County began to diverge. We find that South King County consistently had more reported and estimated cases, COVID-19 hospitalizations, and longer persistence of local viral transmission when compared to North King County, where viral importations from outside drove a larger proportion of new cases. Using mobility and demographic data, we also find that South King County experienced a more modest and less sustained reduction in mobility following stay-at-home orders than North King County, while also bearing more socioeconomic inequities that might contribute to a disproportionate burden of SARS-CoV-2 transmission. Overall, our findings suggest a role for local-scale phylodynamics in understanding the heterogeneous transmission landscape.One Sentence SummaryAnalysis of SARS-CoV-2 genomes in King County, Washington show that diverse areas in the same metropolitan region can have different epidemic dynamics.

Concurrent sexual partnerships (i.e., relationships that overlap in time) contribute to higher HIV acquisition risk. Social capital, defined as resources and connections available to individuals is hypothesized to reduce sexual HIV risk behavior, including sexual concurrency. Additionally, we do not know whether any association between social capital and sexual concurrency is moderated by gender. Multivariable logistic regression tested the association between social capital and sexual concurrency and effect modification by gender. Among 1445 African Americans presenting for care at an urban STI clinic in Jackson, Mississippi, mean social capital was 2.85 (range 1–5), mean age was 25 (SD = 6), and 62% were women. Sexual concurrency in the current year was lower for women compared to men (45% vs. 55%, χ2(df = 1) = 11.07, p = .001). Higher social capital was associated with lower adjusted odds of sexual concurrency for women compared to men (adjusted Odds Ratio [aOR] = 0.62 (95% CI 0.39–0.97), p = 0.034), controlling for sociodemographic and psychosocial covariates. Interventions that add social capital components may be important for lowering sexual risk among African Americans in Mississippi.