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Evaluation of Dual Path Platform optical density in relation to RPR titers and serological response in syphilis: a
Sara Buezo1, Roser Escrig-Sarreta1, Dan Ouchi2
1Section of Communicable Diseases, Hospital Universitari Germans Trias i Pujol, Badalona, Spain; Skin Neglected Tropical Diseases and Sexually Transmitted Infections Section, Fight Infections Foundation, Badalona, Spain.
Objectives:
The Dual Path Platform (DPP) detects treponemal and lipoidal antibodies at the point of care, with an automated reader generating quantitative optical density (OD) values. We assessed the association between DPP OD and RPR titers and post-treatment DPP OD trajectories according to serological cure.
Methods:
We conducted an observational study comprising cross-sectional and longitudinal analyses. The cross-sectional analysis assessed the association between DPP OD and RPR titers in anonymized serum samples. The longitudinal analysis assessed post-treatment changes in DPP OD according to RPR-based serological cure.
Results:
The cross-sectional analysis included 1,222 samples. DPP OD increased with RPR titer, with a quadratic model showing attenuation of the increase at higher titers. Differences between consecutive RPR categories were significant through 1:64 but not at higher titers, with substantial overlap between categories. The longitudinal analysis included 118 participants. Mean DPP OD declined from 89.1 at baseline to 32.4 at week 12, 20.8 at week 24, and 17.0 at week 48. DPP OD declined after treatment in cases with serological cure and increased during recurrent RPR increases.
Conclusions:
DPP OD was quantitatively associated with RPR titer and longitudinal changes reflected RPR-based serological response, supporting further evaluation as a complementary approach for treatment monitoring.
