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

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 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 approached elimination. We show that as districts approach elimination sub-district heterogeneity likely disappears, and district-level summaries may be sufficient to guide decision-making.