Socioeconomic transitions and the spatial dynamics of syphilis transmission in urbanizing China

Syphilis remains a re-emerging sexually transmitted infection in China, with transmission increasingly shaped by regional socioeconomic disparities. Understanding spatial heterogeneity and inter-provincial inequality is essential for equitable disease control.

A balanced panel dataset of syphilis incidence was constructed across 31 provinces in mainland China from 2004 to 2020. Temporal trends were stratified by age and disease stage using joinpoint regression analysis. Spatial clustering patterns of syphilis incidence were evaluated through Global Moran's I and Local Moran's I statistics. To disentangle the socioeconomic determinants of spatial inequality, the Spatial Durbin Model (SDM) for regional spillovers and Multiscale Geographically Weighted Regression (MGWR) were employed to detect structural heterogeneity in risk factors associated with a regime shift external shocks (the Global Financial Crisis and COVID-19).

Syphilis incidence rose substantially (AAPC = 10.69%), driven predominantly by a surge in latent infections among the elderly (≥ 65 years). Spatially, the epidemic exhibited a distinct "westward shift" from affluent coastal regions to the less-developed Northwest. The SDM indicated that economic growth and population mobility generally increased risk, while educational investment exerted a robust protective spillover effect. Crucially, MGWR revealed a deepening spatial inequity in risk mechanisms: Specifically, the 2008 Financial Crisis associated with a regime shift in the less-developed Northwest, transitioning the epidemic from a "wealth-driven" model to a "poverty-driven" risk model. Furthermore, The COVID-19 pandemic inverted the role of transportation, shifting it from a protective factor associated with urban resilience into a primary vector for disease diffusion.

Syphilis transmission in China exhibits clear spatial stratification, where the burden is increasingly shifting to resource-constrained regions. The divergence between consumption-based risk in developed areas and survival-based risk in underdeveloped hinterlands underscores how macroeconomic instability amplifies health inequalities Equity-oriented interventions must prioritize "poverty-driven" transmission pathways and vulnerable older populations to prevent the entrenchment of disease in lagging regions.