Evaluation of a field test for antibodies against Chlamydia trachomatis during trachoma surveillance in Nepal

•Surveillance tools for trachoma are needed.•Tests for antibody to Chlamydial antigen pgp3 show promise.•A lateral flow assay was developed for field assessment of antibody status and compared to multiplex bead array assessment during surveillance surveys in Nepal.•Sensitivity was 40%, specificity was 99%, with inter-reader reliability of 0.65.•Further optimization of the LFA is needed.

PurposeTesting for antibodies to Chlamydia trachomatis has potential as a surveillance tool. Our evaluation compares lateral flow assays (LFAs) during surveillance surveys in Nepal with Multiplex bead array (MBA). Fifty children were randomly sampled from each of 15 random clusters in two districts of Nepal. Finger prick blood samples were collected from 1509 children and tested onsite for anti-Pgp3 antibodies by LFA. The LFA was read at 30 min as negative, positive, or invalid. Tests results were also rated as difficult to read (“equivocal”). Blood was processed at Johns Hopkins University using the MBA.ResultsThe LFA had agreement of 40.0% for MBA-positive samples and 99.3% for MBA-negative samples. Inter-reader reliability was kappa = 0.65 (95% CI = 0.56-0.74). If the equivocal results (7%) could be decreased, reliability could be improved.ConclusionsFurther optimization and testing of the LFA test are needed to improve agreement with MBA and the interpretation of the results.