Are hormonal contraceptive users more likely to misreport unprotected sex? Evidence from a biomarker validation study in Zimbabwe.

We analyzed biomarker validation data of unprotected sex from women in Zimbabwe to determine whether condom and sexual behavior misreporting differs between users of different contraceptive methods. Self-reported sexual behavior was compared with the presence of prostate-specific antigen (PSA) in vaginal fluid, a biomarker of semen exposure. Of the 195 women who were PSA positive, 94 (48 %) reported no sex or only condom-protected sex. Hormonal contraceptive users misreported sexual behavior less than women using non-hormonal methods (45 vs. 67 %, P = 0.03). This misclassification pattern could have implications on the elevated risk of HIV infection associated with hormonal contraception in some studies.