New study ties injected birth control to risk of HIV transmission

A study that could have far-reaching implications on birth control regimens around the world has found an increased risk of HIV transmission for women on injection hormone therapies with an HIV-positive partner.

The Lancet Infectious Disease Journal published the study Monday. The study followed 3,800 couples in Botswana, Kenya, Rwanda, South Africa, Tanzania, Uganda and Zambia. Each couple was sero-discordant, meaning one was infected with HIV and the other was not. The New York Times reports on the findings of the two year long study:

The study found that women using hormonal contraception became infected at a rate of 6.61 per 100 person-years, compared with 3.78 for those not using that method. Transmission of H.I.V. to men occurred at a rate of 2.61 per 100 person-years for women using hormonal contraception compared with 1.51 for those who did not.

This study is one of several which have found an increased risk of HIV transmission connected to injection hormones, such as the Pfizer brand Depo-Provera. In addition to this finding, the study also made an unexpected discovery, reported separately in the Lancet: Pregnancy may also increase HIV transmission risks. Study authors are unsure why that is, whether it is the increased rate of unprotected sexual intercourse or some activity of the virus itself triggered by increased hormones in the body as a result of pregnancy.

Scientists did say that they have been unable to identify specifically why the injection hormones or pregnancy hormones may have such effects, but they noted that studies have found there are increased levels of HIV in the vaginal fluids of women on injection hormones — but that is not correlated with similar findings of virus in the blood of the women.

Injection hormones are popular birth control method in developing countries because the injections can be given once every three months and do not require a doctor in attendance. This means women in rural locations can access the medications without traveling long distances.