In regions where women often die during childbirth and infant mortality is high, the availability of effective birth control is an important tool to protect the health of women and their children. Hormonal contraceptives are effective and affordable, and the convenience of a once-a-month injectable version has made them popular in regions like sub-Saharan Africa. Unfortunately, they may also be increasing rates of HIV acquisition in women as well as transmission to their male partners.
Some smaller observational studies had already noticed higher infection rates in women using hormonal contraceptives, but results were inconsistent and it wasn't clear whether the contraceptives were responsible. A large study published last month lent more credence to this idea, finding that women using injectable hormonal contraceptives were acquiring HIV at nearly twice the rate of those who were not. The study, led by a group of researchers at the University of Washington, followed 3,750 serodiscordant couples (one partner has HIV and the other is uninfected) in seven countries in Africa for two years, and found that for relationships in which the woman was using hormonal contraceptives, the uninfected partner was twice as likely to become infected. And it wasn’t only the women who were more likely to become infected, as some of the previous studies had seen, but also their male partners.
This difference was clear enough to prompt the World Health Organization to schedule a meeting to discuss whether these findings are strong enough to advise women that hormonal contraception can increase the risk for HIV. If this turns out to be the case, it will be a tough situation: without an alternative method to offer, a decrease in the use of effective contraception would likely lead to increased mother-to-child transmission of HIV, without treatment available to everyone who needs it.
Considering the consequences such a shift in public health policy could have, it’s important to confirm that hormonal contraception is really at fault, rather than differences between women who choose to use hormonal contraception and those who do not. Only a controlled trial randomly assigning women to hormonal contraceptives could rule out other influences, but such a trial could be difficult to carry out. This study did try to take into account rates of condom use in their analysis, which were similar between groups, but self-reported data is not always reliable.
If the increased risk is not due to behavioral differences between groups such as condom use, then what is the biological basis for this difference? The study found slightly higher levels of virus in genital fluids of women using hormonal contraceptives, but whether this is enough to account for the results is unclear. Other potential mechanisms have been proposed: for example, studies in monkeys have found that hormonal contraceptives can thin the vaginal epithelium that normally acts as a barrier to incoming pathogens, but their importance in women is unclear. Uncovering the reasons that hormonal contraceptives could increase risk for HIV is an area where research is needed, as is developing or making available alternative methods of contraception. Until then, let’s hope a careful review of the studies that have already been done and an informed public health discussion will help navigate the path forward. (More details on the study’s findings and what they mean for public health policy can be found here).