The study followed 3800 heterosexual couples throughout Botswana, Kenya, Rwanda, South Africa, Tanzania, Uganda, and Zambia. Among each couple, either the man or the woman was already diagnosed as HIV-positive at the start of the study. Researchers measured the number of couples who after 2 years had both members test as HIV-positive, and their corresponding (self-reported) contraceptive use. Condom use was found to be roughly equivalent for both groups of couples (those using hormonal contraceptives and those not). The study found that for couples that used a popular injectable hormonal contraceptive, the rate of transmission to the uninfected partner almost doubled.
WHO (the World Health Organization) will be discussing the issue at a meeting in January, and reevaluating current clinical recommendations on contraceptive use - whether they should be advising female patients more about HIV risk when they prescribe contraceptives.
Personally, I find this study to simply reinforce the importance of condoms. While hormonal contraceptives provide an important tool to help lower unwanted pregnancies, condoms act as a 2-1 barrier against both pregnancy and infection. Most of the confounds I could think of for this study were already controlled for: that women on hormonal contraceptives were not having sex with more partners (because the study only looked at couples), and the fact that condom usage was not more prevalent among couples without hormonal contraception (which would have accounted for their lower rates of HIV transmission). I'm hoping that this will spark research into the field to perhaps look for a biological/chemical mechanism behind the correlation. In the meantime: condoms, condoms, condoms.