Background:
Detection of vaginal Y-chromosome sequences (YCS) has been shown to be a potentially useful biomarker to validate sexual behavior reporting in women.

Objective:
To characterize the effects of condom use during sexual intercourse on the detection of vaginal YCS.

Method:
56 women were asked to abstain from sexual intercourse for 14 days and were instructed by a trained clinician on the proper use of condoms. On day 14, two baseline self-collected vaginal swabs were obtained. On day 15, participants were asked to engage in sexual intercourse with their male partners using condoms. Two additional self-collected vaginal swabs were obtained each on days 16 and 17. Women were asked to keep daily diaries and report on intercourse, contraceptive use, menses, douching, receptive oral sex, and any digital vaginal penetration during the 17-day study period. YCS were detected using the Roche LightCyclerŽ with the use of appropriate controls. Prostate-Specific Antigen (PSA) levels were also measured.

Result:
44 of 56 women completed the study. 39 women (88.6%) had no detectable YCS on any of the collected swabs. After excluding 1 participant with a baseline positive swab, the overall specificity of the YCS assay with condom use was 92% (95% CI: 80%-98%).Three of 4 women (75%) with detectable YCS had reported at least one episode of digital penetration and/or receptive oral sex within 48 hours preceding swab collection (none had detectable PSA). The relative risk of detecting vaginal YCS in women who reported receptive oral sex and digital penetration compared to those who did not was 2.3 (95% CI: 1.1-4.6) and 3.6 (95% CI: 1.6-8.5), respectively.

Conclusion:
Condom use during intercourse appears to prevent vaginal YCS detection. The impact of oral sex on YCS detection needs further characterization.

Implications:
Our data suggest that, in women, YCS detection may be a useful biomarker to validate self-reported condom use.