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Purpose: Population-based prevalence surveys are essential for decision-making on interventions to achieve trachoma elimination as a public health problem. This paper outlines the methodologies of Tropical Data, which supports work to undertake those surveys., Methods: Tropical Data is a consortium of partners that supports health ministries worldwide to conduct globally standardised prevalence surveys that conform to World Health Organization recommendations. Founding principles are health ministry ownership, partnership and collaboration, and quality assurance and quality control at every step of the survey process. Support covers survey planning, survey design, training, electronic data collection and fieldwork, and data management, analysis and dissemination. Methods are adapted to meet local context and needs. Customisations, operational research and integration of other diseases into routine trachoma surveys have also been supported., Results: Between 29 th February 2016 and 24 th April 2023, 3373 trachoma surveys across 50 countries have been supported, resulting in 10,818,502 people being examined for trachoma., Conclusion: This health ministry-led, standardised approach, with support from the start to the end of the survey process, has helped all trachoma elimination stakeholders to know where interventions are needed, where interventions can be stopped, and when elimination as a public health problem has been achieved. Flexibility to meet specific country contexts, adaptation to changes in global guidance and adjustments in response to user feedback have facilitated innovation in evidence-based methodologies, and supported health ministries to strive for global disease control targets.

Trachoma, caused by repeated ocular infection with Chlamydia trachomatis (Ct), is targeted for elimination as a public health problem. Serological testing for antibodies is promising for surveillance; determining useful thresholds will require collection of serological data from settings with different prevalence of the indicator trachomatous inflammation-follicular (TF). Dried blood spots were collected during trachoma mapping in two districts each of Togo and Democratic Republic of the Congo. Anti-Ct antibodies were detected by multiplex bead assay (MBA) and three different lateral flow assays (LFA) and seroprevalence and seroconversion rate (SCR) were determined. By most tests, the district with > 5% TF (the elimination threshold) had five-sixfold higher seroprevalence and tenfold higher SCR than districts with < 5% TF. The agreement between LFA and MBA was improved using a black latex developing reagent. These data show optimization of antibody tests against Ct to better differentiate districts above or below trachoma elimination thresholds.