The most popular contraceptive for women in eastern and southern Africa, a hormone shot given every three months, appears to double the risk the women will become infected with H.I.V., according to a large study published Monday. And when it is used by H.I.V.-positive women, their male partners are twice as likely to become infected than if the women had used no contraception.
The findings potentially present an alarming quandary for women in Africa. Hundreds of thousands of them suffer injuries, bleeding, infections and even death in childbirth from unintended pregnancies. Finding affordable and convenient contraceptives is a pressing goal for international health authorities.
But many countries where pregnancy rates are highest are also ravaged by H.I.V., the virus that causes AIDS. So the evidence suggesting that the injectable contraceptive has biological properties that may make women and men more vulnerable to H.I.V. infection is particularly troubling.
The study, led by researchers at the University of Washington and published in The Lancet Infectious Diseases, involved 3,800 couples in Botswana, Kenya, Rwanda, South Africa, Tanzania, Uganda and Zambia. In each couple, either the man or the woman was already infected with H.I.V. Researchers followed most couples for two years, had them report their contraception methods, and tracked whether the uninfected partner contracted H.I.V. from the infected partner, said Dr. Jared Baeten, an author and an epidemiologist and infectious disease specialist.
The research was presented at an international AIDS conference this summer, but has now gained traction, scientists said, with publication in a major peer-reviewed journal.
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.
While at least two other rigorous studies have found that injectable contraceptives increase the risk of women’s acquiring H.I.V., the new research has some strengths over previous work, said Charles Morrison, senior director of clinical sciences at FHI 360, a nonprofit organization whose work includes researching the intersection of family planning and H.I.V.