July 14, 2003
Lavreys et al. updated their impressive cohort study of Kenyan commercial sex workers and their risk of HIV-1 infection. A major goal of this cohort study is to examine the relationship between hormonal contraceptives and the risk of sexually transmitted infections, including HIV-1. Several years ago, they reported an association between depot methoxy-progesterone acetate (DMPA) and HIV-1 acquisition. In this abstract, they presented the 10-year follow-up to this cohort.
The analysis included 1,272 women who were followed for a total of 2,931 person-years. The women received monthly testing for sexually transmitted infections and HIV in addition to safer sex counseling and condoms. Most women used some form of contraception, and the choice of contraception was not randomized. The primary analysis compared the rate of HIV-1 acquisition in women using hormonal contraception (DMPA or oral contraceptives) to that of women either using no contraception or who had undergone surgical sterilization (e.g., bilateral tubal ligation).
Not surprisingly, they found a very high overall rate of HIV-1 acquisition: 8.5 infections/100 person-years. Consistent with their previous study, the rate of HIV-1 acquisition was 1.8 times higher for those women using DMPA, a very significant result. A new finding of this study was a significant association between oral contraceptive use and HIV-1 acquisition, a rate 1.5 times that of women using surgical sterilization or no contraception. The authors corrected for any differences between the groups in sexual behavior, other sexually transmitted infections and condom use that might explain these results.
The authors noted that very few women became pregnant during the study. Given that sexual behavior is difficult to measure accurately, it is reasonable to suspect that women using no contraception may have had different sexual behaviors than women using effective contraception, which may have explained some of the differences. The authors did not address the mechanism of this relationship, but other studies have provided insight. DMPA causes a thinning of the vaginal epithelium and decreases peroxide-producing lactobacilli, which are protective against HIV acquisition. Oral contraceptives increase cervical ectopy (extension of columnar epithelium onto the exocervix), which is also associated with increased HIV acquisition.
It is not at all clear what should be done with this information. Hundreds of millions of women are on hormonal contraception worldwide. In many parts of the world, including Kenya, pregnancy is associated with a significant risk of complications and death. Also, it is not known whether these results will apply to other groups of women who have less exposure to HIV. It does, however, indicate an important area for HIV prevention -- modifying the risk of HIV-1 infection in women using hormonal contraception.
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