Brewer, D. D., Potterat, J. J., Gisselquist, D., & Collery, S. (2010). Vaginal tenofovir gel trial results suggest substantial nonsexual HIV transmission. WebmedCentral EPIDEMIOLOGY, 1(12):WMC001292 (http://www.webmedcentral.com/article_view/1292).
Abdool Karim and colleagues demonstrated that vaginal tenofovir gel provides partial protection against HIV in South African women. However, the study design of their double-blind, randomized, placebo-controlled CAPRISA 004 trial did not allow for determining the mode of HIV acquisition for participants with incident infection. The available evidence suggests substantial nonsexual transmission. Trial participants' reported exposure to HIV through penile-vaginal sex, at the aggregate level, was unrelated to HIV incidence over time. Moreover, the CAPRISA 004 trial data imply a questionably high nominal per act transmission probability for coital acts without a condom (1.8% in the tenofovir gel arm and 3.0% in the placebo arm). Based on the results of dosing studies, the vaginal tenofovir gel appears to be a somewhat inefficient vehicle for delivering tenofovir systemically, thereby serving to prevent HIV acquisition from either blood or sexual exposures. Further analysis of the trial data and making the full trial protocol and data public would allow competing interpretations of the CAPRISA 004 results to be investigated. New trials that include critical design features for determining modes of HIV transmission would provide the most definitive evidence.