Background When Chlamydia trachomatis (CT) is detected after adequate treatment, this may reflect treatment failure or re-infection due to sexual re-exposure. For sexual exposure, researchers rely on self-reported data. Biomarkers such as Y-chromosomal DNA (Y-DNA) from vaginal and rectal samples may be used to support the validity of the self-reported sexual exposure data. The aim of this study was to validate detection of Y-DNA in a cohort of treated female CT patients, the Femcure study.

Methods Participants provided self-swabs for various days after treatment. For each swab, self-reported last unsafe (vaginal or rectal) sexual exposure (LUSE) was recorded in days (range t0-t14). Samples consisted of vaginal (n=120: 20 swabs at t=0,1,2,3,4; and 20 swabs at t=7,8) and rectal (n=43, 6 swabs at t0–1; 15 swabs at t2–5 and 22 swabs at t6–14) CT negative swabs in Roche COBAS PCR uniswab media (FemCure 2016–2017). CT negative human semen was used for spiking experiments. Quantitative detection of Y-DNA was performed using Quantifiler® Duo DNA Quantification Kit.

Results Samples with realistic spiked concentrations of ∼0.5 ng/microliter Y-DNA remained stable and detectable until at least 35 days in the medium at 4°C. For vaginal swabs, detection of Y-DNA correlated inversely with LUSE: the Y-DNA detection percentage was 90%, 60%, 30%,10%, 20% at t=0,1,2,3,4, and 5% at t7,8. In anal swabs, detection was 33% at t0–1 and 13% at t2–5 and t6–14.

Conclusion Y-DNA correlates strongly with LUSE in vaginal swabs, with high Y-DNA detection in the first 48 hours. Y-DNA detection data can be used to support self-reported sexual exposure data used in most research. The detection of Y-DNA in anal swabs has to be further validated as our study only included a limited number of anal samples at early time-points.

Disclosure No significant relationships.