Original research articleHormonal contraception and HIV prevalence in four African countries
Introduction
The relationship between hormonal contraception and susceptibility to the heterosexual transmission of HIV in developing countries remains controversial and has been the source of several reviews [1], [2], [3], [4], [5]. Part of the controversy stems from the variety of the epidemiological studies: some studies distinguish between oral contraceptives based on estrogens, and injectables or implants based on progestins, but others merged them together; some studies focused on young women, others on older women or women of any age; some studies focused on high risk or heavily exposed women, for example, commercial sex workers (CSWs) or sexually transmitted diseases (STDs) clinic patients, while others deal with general populations or subgroups: attendants of antenatal clinics or users of family planning clinics (FPC). Many studies had small sample size and not enough statistical power to confirm the effect. In addition, controls used for multivariate analysis were not always the same, and some are directly linked to the risk of HIV/AIDS, in particular patients with STDs.
First observations made in the early 1990s suggested an increased risk associated with hormonal contraception. In Thailand, a prospective study conducted among CSWs found a high risk ratio associated with the use of depot medroxyprogesterone acetate (DMPA) [6]. In Kenya, a similar prospective study among CSWs found a high risk ratio associated with oral contraceptives [7]. However, another study conducted later in Kenya found no effect of oral contraception but a significant effect of DMPA [8]. In Rwanda, a prospective study of pregnant women recruited in antenatal clinics found a significant effect of oral contraception [9]. A meta-analysis conducted in 28 countries suggested a 20% increased risk of HIV infection associated with oral contraception, and somewhat higher risks were found in Africa and when studies were conducted more rigorously [1]. Another review of 15 prospective studies concluded that hormonal contraception, and in particular DMPA, could increase the risk of HIV-1 acquisition among high-risk women but not in the general population [5]. Of course, various biases might be involved in these studies, since numerous interactions could exist between sexual behavior and the use of hormonal contraception [10].
Biological studies have also shown the complexity of the mechanisms involved in the differential susceptibility to HIV infection associated with hormonal contraception and the possible differential effects of estrogen-containing (pill) vs. progestin-only contraceptives (DMPA, implants). Simian models showed that simian immunodeficiency virus (SIV) transmission is possible through the vaginal epithelium [11] but that an intact lining is a formidable barrier to the virus [12]. Therefore, one could hypothesize that breaks in, or thinning of, the vaginal epithelium may be responsible for increased risk of vaginal transmission [13]. In simian models, progesterone leads to reversible vaginal thinning, whereas estrogens seem to be associated with thickening of the vaginal epithelium [14]. Sexual hormones can modify susceptibility to SIV among nonhuman primates, and progesterone may facilitate its vaginal transmission [15], whereas estrogens may be protective [16], [17]. In humans, the mechanisms might be somewhat different, and the physiological effects of progestins may be smaller than in monkeys [18], [19], [20]. Precise mechanisms by which hormones might modulate HIV susceptibility remain unclear [4]. Furthermore, age might be an important cofactor since the vaginal epithelium of adolescent and very young women is thinner than at older reproductive ages. In animal models, age was found as a factor of thickness and integrity of the vaginal epithelium [21]. In epidemiological studies, younger women appear most susceptible to HIV-1 infection, and a large proportion of HIV infections occurs prior to age 25 [9], [22].
The aim of this article is to help resolve these controversies from a demographic perspective. Some countries in sub-Saharan Africa have among the highest rates of HIV seroprevalence in the world and also use large amounts of hormonal contraception. In particular, young women of Southern and Eastern Africa often use DMPA and have high rates of HIV seroprevalence. Although use of DMPA among 15- to 24-year-old women is not higher than in many Latin American countries, where HIV seroprevalence is much lower, it might still be a risk factor. The Demographic and Health Surveys (DHS) provide an opportunity to investigate the relationship between HIV seroprevalence and hormonal contraception in the general population, since they provide both information for large samples of women and numerous potential cofactors. They permit the comparison of HIV seroprevalence among young women according to their pattern of use of hormonal contraception.
Section snippets
Study population
Demographic and Health Surveys are conducted on nationally representative samples of women in their reproductive ages, with sizes ranging from 3000 to 20,000 (see DHS Web site for more details [23]). They provide data on numerous aspects of demographic and health characteristics, in particular the use of contraceptive methods, and since 2001, some of the recent surveys include data on HIV seroprevalence. In Africa, 12 surveys with information on HIV were available at the time of this study,
Results
The samples in the four countries investigated (Kenya, Malawi, Lesotho and Zimbabwe) cumulated 4549 women aged 15–24 years, sexually active and with known HIV serologic status. The HIV prevalence differs between the countries and ranges from 8.2% in Kenya, 11.8% in Malawi, 18.9% in Zimbabwe, to 20.2% in Lesotho (Table 1). Contraceptive prevalence is rather high for African countries and varies from country to country. The proportion of women who ever used any method ranges from 47% in Kenya to
Discussion
Representative samples of the populations in the four countries investigated show that ever use of DMPA increased somewhat the risk of HIV among young women but that ever using the pill had no effect. The DMPA effect does not seem to be due to a selection bias associated with using contraception, since both traditional methods and the pill had no associated risk, since the effect was consistent in the four countries investigated and since the results were robust to various controls added in the
Acknowledgment
This study was not funded from an outside sort; all the authors are supported by their institutions and the study had no external cost.
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