Population-level impact of hormonal contraception on incidence of HIV infection and pregnancy in women in Durban, South Africa.

OBJECTIVE To estimate the potential impact of using hormonal contraceptives on rates of infection with human immunodeficiency virus type 1 (HIV-1) and pregnancy by theoretically removing the use of hormonal contraceptives from a study population. METHODS A prospective cohort study included 3704 HIV-negative women who were enrolled in two biomedical trials that tested two vaginal microbicides (PRO 2000 and Carraguard®) for the prevention of HIV-1 in Durban, South Africa, in 2004-2009. Cox proportional hazards regression models along with partial population attributable risks (PARs) and their 95% confidence intervals (CIs) were calculated to assess the relative population-level impact of the use of hormonal contraceptives on HIV-1 seroconversion rates and on pregnancy rates. FINDINGS Women who reported using hormonal contraceptives at enrolment in the trial had a higher risk of HIV-1 seroconversion (adjusted hazards ratio: 1.24; 95% CI: 0.97-1.58) than women who reported using other types of contraceptives at enrolment. At the population level, the use of hormonal contraceptives (pills or injectables) at baseline and during study follow-up accounted for approximately 20% (95% CI: 16-22) of HIV-1 seroconversions. However, the partial PAR indicated a relative impact of 12% (95% CI: 9.0-15.7). On the other hand, 72% (95% CI: 66-77) of the pregnancies could have been avoided if all women had used hormonal contraceptives. CONCLUSION Women using hormonal contraceptives need comprehensive counselling on simultaneous prevention of HIV-1 infection.