Optimization of a rapid test for antibodies to the Chlamydia trachomatis antigen Pgp3.

Serological surveillance for trachoma could allow monitoring of transmission levels in areas that have achieved elimination targets. Platforms that allow testing in basic laboratories or testing of easy-to-manage samples such as dried blood spots would contribute to the feasibility of serologic testing. Blood from 506 1-12-year-olds in 2 villages in Kongwa district, Tanzania, was tested for antibodies against the antigen Pgp3. Whole blood, plasma, and dried blood spots (DBS) were tested in lab and field settings using a cassette-enclosed Pgp3 lateral flow assay (LFA-cassette) and a pared-back "dipstick" assay (LFA-dipstick). DBS were also tested with a bead-based multiplex assay (MBA). There was no significant difference in antibody positivity between the MBA and either LFA format (ranging from 42.5% to 48.4%). Interrater agreement between an expert rater and 3 different raters in field and lab settings was uniformly good, with Cohen's kappa >0.81 in all cases.