Background: Self-reported measures of sexual behavior are subject to nontrivial reporting biases.
Objective: The objective of this study was to develop a behavioral biomarker of recent sexual activity among females that is inexpensive, easily administered, and can be used in low sexually transmitted disease prevalence populations.
Methods: We developed a polymerase chain reaction (PCR) assay to detect Y chromosome (Yc) fragments. The Yc primers were developed against a 200-basepair (bp) microsatellite repeat sequence, which is unique to the male genome. A standard PCR technique was used. Assay sensitivity was determined quantitatively using donated semen samples. To assess longevity of detectability, we recruited female subjects in monogamous relationships. Seventeen subjects had unprotected intercourse followed by 3 weeks of abstinence from vaginal intercourse. Self-administered vaginal swabs (SAVS) were collected every other day. In addition to the swabs, subjects kept daily sexual diaries. Swabs were processed by semiquantitative PCR, and Yc decay curves were determined for each subject. The half-life of Yc in vaginal fluid was calculated on the collection of individual decay curves by a random-effects regression model approach.
Results: The sensitivity of our Yc-PCR assay was determined to be 5 copies of Yc. In the longevity studies, Yc was detectable in SAVS up to 15 postcoital days (PCD). Mean Yc DNA concentration in SAVS eluate followed an exponential decay pattern for each subject. Mean concentrations were 66.7 ng/mL at PCD-1, 20.6 ng/mL at PCD-7, and 4.5 ng/mL at PCD-15. The estimated half-life for Yc clearance was 3.83 days.
Conclusion: The swab-based Yc-DNA PCR assay can detect coitus in women for a 2-week retrospective period. This can be used to validate sexual behavior-reporting and condom use in women and promises to be a useful tool in sexual behavior research.