Fig. 1

Individual elements of the composite measure of adherence, protocol compliance, and semen exposure. Returned, used TFV 1% gel applicators were swabbed with three swab heads to capture biomarkers and residual drug on the barrel of the applicator. The first swab head was used to detect of vaginal bacterial DNA and y-chromosomal DNA. The second swab head was used to detect the presence of CK4 in vaginal cells left on the applicator. The third swab head was used for detecting residual TFV by LC–MS/MS and FTIR spectroscopy. More details have been previously published [10, 13]