Using objective markers to assess participant behavior in HIV prevention trials of vaginal microbicides.

The need to verify participant behavior exists in any study in which behavior may affect outcomes. In vaginal microbicide trials, the act of having sex and the use of study products and condoms all affect the risk of acquiring HIV/sexually transmitted infections (STIs). Until now, these behaviors have been assessed using self-reports. But self-reports are limited by participant cooperation in answering questions, imperfect recall, and social desirability biases. Biomarkers are increasingly being used in medicine to reduce the time and resources needed to bring a drug to market. The use of biomarkers in vaginal microbicide trials has been proposed as a means of assessing factors that affect the risk of sexual acquisition of HIV/STIs, namely, the presence of preexisting infection, cervicovaginal inflammation, and the presence of HIV/STIs. Biomarkers for some of these already exist. What are needed are validated markers of behaviors that might affect risk, namely, markers for sexual behavior and for the use of study products and condoms. Validating and working out the logistics of collecting such markers in large trials will be a challenge. But finding objective markers for behavior may help improve adherence measurement during a trial and is a rate-limiting step in the field of vaginal microbicides. Resources and funding should be mobilized to develop and validate markers of sexual behavior and product use as a high priority in vaginal microbicide research.