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

Purpose: Testing 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. Results: The 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. Conclusions: Further optimization and testing of the LFA test are needed to improve agreement with MBA and the interpretation of the results.