What should be the policy on hormonal contraceptives in settings where the transmission of HIV is a serious concern – e.g. in sub-Saharan Africa? Some studies have indicated the possibility of added risk of heterosexual transmission between sero-discordant partners where this method of contraception is used. But given the need to balance that risk against the known benefit of hormonal contraception in reducing vertical transmission through unwanted pregnancy (also an important plank of public health policy), it is important to be as precise as possible about the extent and nature of the risk. So the WHO has called for further research in this area.
Highly relevant to these concerns is a large prospective cohort study of 3,790 African heterosexual HIV 1 sero-discordant couples in seven sub-Saharan countries, recently reported in The Lancet Infectious Diseases. This places the risk of transmission where hormonal contraception is used at approximately double – an adjusted hazard ratio of 1.98 of transmission from male to female partner, and of 1.97 from female to male. It should be added that it is hormonal contraception by injection that is primarily at issue here; the number of participants taking oral pills was insufficient to warrant any firm conclusions. These results bear out earlier findings concerning male to female transmission. They also establish, for the first time, a similar level of risk for female to male transmission.
The causes of this added risk are hard to determine with any precision. The participants in the present trial were recruited on the back of two longitudinal studies of HIV-1 incidence (2004-2010) – and required to complete standard questionnaires about their current contraceptive method at quarterly visits. The authors draw attention to possible physiological factors that could be operating alongside behavioural ones in increasing the risk for hormonal contraception users. But, as the authors themselves point out, it is hard to see how the respective influence of these or other factors could be determined without assigning groups of participants to specific contraceptive methods for the duration of the study – which is hardly feasible, or ethical!
There remains the question of how these findings should be embodied in health policy. What is the balance that should be reached between the risks of vertical and horizontal transmission? The authors confine themselves to emphasizing the importance of integrating contraceptive and HIV counselling and testing – as well as recommending that women should be warned of a potentially increased risk of horizontal transmission, and the value of dual protection (i.e. consistent condom use in addition to hormonal methods).
Renee Heffron, Jared M. Baeten et al., “Use of hormonal contraceptives and risk of HIV-1 transmission: a prospective cohort study” in The Lancet Infectious Diseases, available online 3rd October, 2011