Evaluation of the reproducibility of a serological test for antibodies to Chlamydia trachomatis pgp3: A potential surveillance tool for trachoma programs

Purpose: Serological testing for antibodies to Chlamydia trachomatis pgp3 is being evaluated as a tool to use for trachoma surveillance. There are limited data on the reproducibility of the test results using a multiplex platform. Methods: We tested the reproducibility of a serologic test for C. trachomatis pgp3 in 6 dried blood spots collected from a random sample of 45 children from a trachoma endemic area. The spots were tested on a multiplex bead array platform, using one bead set twice, using another bead set at the same time as the first, and using the same bead set twice on different days separated by several months. Seropositivity was defined using ROC analyses from the same external controls for both bead sets. We compared the mean fluorescent intensity unit minus background (MFI-BG) results using the intraclass correlation coefficient (ICC), and analyzed the concordance of seropositivity designation using the kappa statistic. Results: The tests using the same bead set were highly correlated, ICC = 0.997 (0.995–1.00). Even tested months apart, the slight loss of signal was not statistically significant (p = 0.06). The test of the two different bead sets showed high correlation, but the differences in MFI-BG was statistically significant. However, the serostatus of the children was unchanged comparing the seropositivity using one bead set compared to a second bead set. Conclusion: The reproducibility of the multiplex bead array for serological testing of antibodies to Chlamydia trachomatis pgp3 is high when the same bead set is used for testing.