RESUMO
BACKGROUND: Prostate-specific antigen (PSA), a biomarker of vaginal semen exposure, is less susceptible to bias than self-reported condom use behaviors. 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 study conducted in Vietnam, 2017 to 2020, of 500 different-sex couples using condoms and no other contraceptive method to prevent pregnancy for 6 months. We assessed enrollment and 6-month data from vaginal swabs and questionnaires from both partners. We calculated Prevalence-Adjusted Bias-Adjusted Kappa (PABAK) to evaluate agreement of men's and women's reports. Among couples with detected PSA, we assessed partner concordance of RCS reporting. RESULTS: At enrollment (n = 499), 79.8% of couples reported no RCS, 16.4% reported RCS, and 3.8% had partner-discordant reports (PABAK, 0.93; 95% confidence interval, 0.91-0.97). At 6 months (n = 472), 91.7% reported no RCS, 5.7% reported RCS, and 2.5% had partner-discordant reports (PABAK, 0.98; 95% confidence interval, 0.96-1.0). Among couples with detected PSA at baseline (11%, n = 55), 36% reported no RCS, 55% reported RCS, and 6% had discordant reports; at 6 months (6.6%, n = 31), 58% reported no RCS, 35% reported RCS, and 3% had discordant reports. CONCLUSIONS: We observed high agreement regarding condomless sex within couples in a population using condoms as contraception in Vietnam; however, a high proportion of couples with detected PSA had both partners reporting no RCS, indicating that concordant reporting of no RCS does not indicate lack of semen exposure.