Vaginal microbicide adherence biomarkers should be validated – Authors' reply

Only one validation study has been done with the staining method used in this efficacy trial.2 Women might have washed used applicators before returning them to the clinic; there are no published data on the validity of the stain on washed applicators.2,3 Furthermore, self-reported adherence was based on use during the last sex act only, as a proxy for all sex acts between quarterly follow-up visits, and reported sex acts were for the previous 2 weeks only. Recognising the limitations of selfreporting and the implementation of the applicator test in the Carraguard phase III trial, the Population Council is doing a simulated microbicide trial in which applicator test results are compared with self-reported gel use by women randomised to either monthly face-to-face interviews or audio computer-assisted self-interviewing.