Unprotected sex in an STD clinic population: agreement between self-reported condom use and PCR detection of y-chromosome in vaginal fluid

Alia A. Al-Tayyib, University of North Carolina at Chapel Hill
William Miller, University of North Carolina at Chapel Hill
Jonathan M. Zenilman, Johns Hopkins University

Objective: To assess agreement between self-reported condom use and results of a PCR assay developed to test for presence of Y-chromosome fragment in vaginal fluid. Study Design: In a cross-sectional study, 477 women, ages 15-39 years, attending an urban STD clinic provided self-collected vaginal swabs for Y-chromosome testing and completed an audio computer-assisted self-interview in which they self-reported condom use behaviours. Y-chromosome is detectable by PCR in vaginal fluid up to 2 weeks post-coitus. Results: Fair agreement was found between self-reported condom use in the past two weeks and assay result (kappa = 0.29, 95% confidence interval: 0.20, 0.38). Of the 34% with discordant results, 15.7% reported consistent condom use but tested positive for Y-chromosome while 18.4% reported no condom use and had a negative assay result. Conclusions: A combination of biological markers of exposure to seminal fluid and self-reported behaviours may provide a more valid measure of condom use in at risk populations.