(P30) Validity of self-reported recent condomless sex among couples in Vietnam

Background: Measurement of condom use via self-reports is prone to social desirability and recall bias. Prostate-specific antigen (PSA), a biomarker of vaginal semen exposure, is less susceptible to bias than self-reporting. We examined the agreement of self-reported recent condomless sex (RCS) within couples and how these reports related to PSA detection.

Methods: We analyzed data from a randomized controlled trial conducted in Vietnam in 2017–2020 of 500 different-sex couples using condoms, and no other contraceptive method, to prevent pregnancy for six months. Women completed questionnaires and had vaginal swabs collected at enrollment, 2, 4, and 6 months. Men completed questionnaires at enrollment and 6 months. Semen exposure was determined by PSA positivity of vaginal swabs. We defined RCS as penile-vaginal sex without a condom within two days, based on independent reports from both men and women. We calculated Prevalence-Adjusted Bias-Adjusted Kappa (PABAK) to evaluate agreement of men’s and women’s reports. Among couples with detected semen exposure, we assessed concordance of RCS reporting of men and women (both report RCS, neither reports RCS, discordant reports).

Results: One couple was excluded for missing data. At enrollment (n=499), 79.8% of couples reported no RCS, 16.4% reported RCS, and 3.8% had discordant reports (PABAK 0.93; 95% CI 0.91, 0.97). At 6 months (n=472), 91.7% reported no RCS, 5.7% reported RCS, and 2.5% had discordant reports (PABAK 0.98; 95% CI 0.96, 1.0). Among couples with detected PSA at baseline (11%, n=55), 36.4% reported no RCS, 54.6% reported RCS, and 9.1% had discordant reports; at 6 months (6.6%, n=31), 58.1% reported no RCS, 35.5% reported RCS, and 6.5% had discordant reports.

Conclusions: Research in other settings has demonstrated poor agreement between men and women regarding condom use; however, we saw high agreement within couples in a population using condoms as contraception in Vietnam. A high proportion of couples with detected PSA had both partners reporting no RCS, indicating that concordant reports of no RCS is does not imply lack of semen exposure.