Sub-district spatial heterogeneity in trachoma seroprevalence as populations approach elimination

Abstract Programmatic decisions regarding surveillance and intervention for trachoma are made at the district level, reflecting an implicit assumption that transmission within districts is sufficiently homogeneous. However, as trachoma transmission declines, residual pockets of transmission may become spatially heterogeneous at sub-district scales. Using cluster-level data from 12 districts in Amhara, Ethiopia (2019–2023), we assess the spatial structure of Pgp3 antibody responses, a sensitive measure of infection transmission. Spatial clustering was evident in higher prevalence districts but diminished as populations approach elimination. We show that as districts approach elimination sub-district heterogeneity disappears, and district-level summaries are likely sufficient to guide decision-making.