Hormonal contraceptive associated with increased risk of HIV infection

Women using either the oral or injectable forms of the contraceptive DMPA are at a higher risk of HIV infection than those not using these methods, according to a study published in the March 5^th issue of the journal AIDS.

These “concerning” findings were the result of a ten-year study among HIV-negative women attending a prostitute clinic in Mombasa, Kenya, and were initially reported as a poster presentation at last summer's IAS Conference in Paris.

Until now, there have been insufficient data to make recommendations to women regarding the effect of contraceptive choices on the risk of HIV infection. However, this thorough prospective trial (now peer-reviewed) included monthly measurements of HIV status, contraceptive use, sexual behaviour and sexually transmitted infections (STIs), minimising the potential for bias.

The study began in 1993, and reported five years ago that women who used the injectable contraceptive depot medroxyprogesterone acetate (DMPA) were twice as likely to become infected with HIV than those women who did not use any contraceptives, after controlling for sexual behaviour, condom use and STIs.

Ten years on, with 1498 women in the cohort and 15,428 follow-up visits (reflecting 2931 person-years of follow-up) 248 women have now seroconverted, allowing for much more informed data.

Although the study was open to women attending a prostitute clinic, actual sexual activity was relatively low, with a median of one sexual partner and two sexual encounters per week. This was because most of the women supplemented their bar-work income with part-time commercial sex work. None of the women reported injection drug use and only three practised anal sex, making heterosexual vaginal intercourse the main HIV risk factor for more than 99% of the cohort.

The researchers used multivariate Cox proportional hazards models (controlling for sexual behaviour, condom use and STIs) to analyse the association between hormonal contraceptive use and the incidence of HIV infection.

Similar to their 1993 findings, DMPA use was associated with a risk that was 1.8-times greater than women using no hormonal contraceptives (95% CI 1.4 - 2.4; P <0.001).

Additionally, the use of the oral contraceptive pills was associated with a 1.5-times greater risk of HIV infection compared with women not using contraceptives (95% CI 1.0 - 2.1; P = 0.04).

Women who used the implantable contraceptive Norplant were considered to be at increased risk (Hazard Ratio: 1.6; 95% CI 0.5 - 5.7; P = 0.5), but the findings were not statistically significant.

There was no increased risk seen in women using an intrauterine device (IUD), which suggests that the use of contraceptives does not lead to higher HIV risk across-the-board.

The authors caution, however, that although this study found that the use of both injectable and oral contraceptives may increase the risk of HIV acquisition, independent of sexual behaviour and STI exposures, these results may be most applicable to women at high risk.

Nevertheless, although these women changed partners weekly, their average sexual frequency was similar to that reported in surveys among the general population of African women. Since the majority of the cohort used condoms sporadically for STI protection, regardless of contraceptive use, these results may reflect real-world risk more accurately than other studies performed amongst low-risk populations, such as women who attend family planning clinics.

The authors conclude that “given the widespread use of hormonal contraception in areas of high HIV-1 prevalence, our findings are concerning. Regardless of the method women choose for pregnancy prevention, healthcare providers must emphasise that condoms are the only method proved to prevent HIV-1 transmission. Women who use hormonal contraception, especially those at high risk of HIV-1, should be especially encouraged to use condoms consistently.”

Further information on this website

Hormonal contraceptives increase risk of HIV infection - news story

Contraception and women's HIV risks - news story

Pregnancy & Contraception - fact sheet