Background: Carrageenan has been shown to inhibit Human papillomavirus (HPV) infection in vitro. A carrageenan containing vaginal microbicide, Carraguard developed by the Population Council was tested for its efficacy in prevention of genital HPV infection in South African women. This was a sub-study using data from the Population Council's randomised, double-blind, placebo-controlled trial which tested the efficacy of Carraguard to prevent HIV infection. Carraguard was not found to prevent HIV infection.

Methods: Participants in the study received Carraguard gel or placebo (methyl cellulose gel) plus condoms, and were instructed to use gel plus condoms during each act of vaginal intercourse. Oncogenic, high-risk, HPV (HR-HPV) detection was performed on study end cervical samples from 1723 women by Digene Hybrid Capture 2 analysis. Logistic regression analysis was used to assess the relative risk of contracting HR-HPV for individuals receiving Carraguard relative to individuals receiving placebo.

Results: End trial prevalence of HR-HPV was 23.2%. [95% CI(21.3, 25.2)]. In Carraguard users HR-HPV prevalence was 23.5% [95% CI (20.8, 26.3)] and 23.0% [95% CI (20.2, 25.8)] inplacebo users. Significant risk factors for HR-HPV infection were younger age, being single, an abnormal pap smear, multiple sexual partners (woman and primary partner) and promiscuous behaviour without the use of a condom. After adjusting for risk factors, Carraguard was found protective for HPV infection for women who inserted >80% of their returned applicators of test product with >30% confirmed covered sex acts. Within the latter category, Carraguard was almost 50% more efficacious than placebo. Carraguard users were 0.529 as likely to contract HR-HPV [95% CI (0.304, 0.920)] as women who used placebo (P=0.0176).

Conclusions: Carraguard was shown to be effective in protecting against vaginal transmission of HR-HPV. To our knowledge, this is the first report of successful protection against genital infection by a vaginal microbicide