Strengthening laboratory capacity for trachoma serological surveillance in Amhara, Ethiopia: Use of the lateral flow assay

Trachoma programs are increasingly using serological tools to complement clinical indicators and to measure current and historical transmission of Chlamydia trachomatis (Ct). In January 2024, the Amhara Trachoma Program in Ethiopia implemented the Pgp3 lateral flow assay (LFA) for trachoma serosurveillance through the regional public health laboratory system. Three Amhara Public Health Institute Trachoma Molecular Laboratory scientists were trained and passed competency testing on the assay. The scientists then conducted LFA testing on dried blood spot (DBS) samples collected during a December 2023 trachoma impact survey in Tach Gaynt, Amhara. During testing, 2,542 DBS samples were processed over 12 days. Age-specific seroprevalence and seroconversion rates (SCRs) were estimated. Among children ages 1-5 years, seroprevalence was 20.8% (95% confidence interval [CI]): 17.4-24.7%), and the SCR was 7.9 per 100 child-years (95% CI: 4.6-13.5). Among children ages 1-9 years, seroprevalence was 26.0% (95% CI: 22.9-29.3%), and the SCR was 7.0 per 100 child-years (95% CI: 4.6-10.6). Seroprevalence among individuals ages 15 years and older was 85.8% (95% CI: 83.9-87.4%). Trachomatous inflammation-follicular prevalence among children ages 1-9 years (TF1-9) was 28.6% (95% CI: 22.1-35.4%), and Ct infection among children ages 1-5 years was 5.7%, suggesting ongoing transmission. The concordance between LFA results, TF1-9 prevalence, and Ct infection prevalence supports the utility of the LFA for trachoma surveillance in Ethiopia, with Pgp3 LFA testing performed in a regional public health laboratory. Integrating LFA-based serology into the Ethiopia national trachoma surveillance systems offers a scalable approach to guide programmatic decisions and support trachoma elimination as a public health problem.