Hormonal contraception does not increase HIV infection risk

A study published in the January 2^nd 2007 edition of AIDS has found that there is no association between the use of hormonal contraception and the risk of HIV acquisition. The study authors believe that this finding will “provide reassurance for women in a setting of moderate and high HIV prevalence who need effective contraception.” The study did, however, have one surprising result: women who used hormonal contraception and were negative at baseline for herpes simplex virus-2 (HSV-2), an ulcerative sexually transmitted infection (STI) associated with an increased risk of HIV acquisition, had a significantly increased risk of HIV acquisition than women who are non-hormonal contraception users and also HSV-2-negative.

Over 100 million women worldwide use hormonal contraception in either a combined oral contraceptives (COC) containing estrogen and progestin or a progestin-only injectable contraceptive depot-medroxyprogesterone actate (DMPA). The use of hormonal contraception is increasing in areas of high HIV prevalence. Therefore establishing if there is a link between the use of hormonal contraception and the risk of HIV infection is a matter of important public health concern.

Although the question has been explored in numerous studies previously, these yielded conflicting results and the studies were beset by methodological problems. Therefore an international team of investigators designed a statistically highly-powered, prospective study involving over 6,000 women in Zimbabwe, Uganda and Thailand to see if users of hormonal contraceptives had an increased risk of HIV acquisition. A sub-study looked at the effect of STIs on the risk of HIV infection amongst users of hormonal contraception.

The women, all of whom were aged between 18 and 35 years (with a median age of 25), were recruited and followed between 1999 and 2004. Follow-up was conducted every twelve weeks for 15 – 24 months and included tests for HIV, HSV-2 and other STIs. Women were also asked to provide details of their relationship status and sexual behaviour.

A total of 213 women became infected with HIV during the course of the study. However, the investigators’ analysis revealed that neither the COC hormonal contraception (hazard ratio 0.99), nor DMPA hormonal contraception (hazard ratio 1.25) were significantly associated with the risk of HIV acquisition. Among the factors associated with incident HIV infection were not living with a partner (p = 0.008), younger age (p = 0.001), behavioural risk (p = 0.002), and partner’s behavioural risk (p < 0.001).

In further analysis, the investigators found that there was no significantly different risk of HIV acquisition between COC and DMPA methods of hormonal contraception.

The infections trichomonas, bacterial vaginosis, candida, chlamydia, and gonorrhoea did not increase the risk of hormonal contraceptive users becoming infected with HIV.

As expected, women who were infected with HSV-2 at baseline were significantly more likely to become infected with HIV (p = 0.003). But when the investigators restricted their attention to women who were HSV-2-negative at baseline their analysis yielded a surprising result – women who used both forms of hormonal contraception had a significantly increased hazard of infection with HIV (COC, hazard ratio: 2.48; DMPA, hazard ratio: 4.96) compared to women who did not use hormonal contraception.

“We found no overall association between the risk of hormonal contraception and the risk of HIV acquisition”, comment the investigators. However they add, “the modifying role of HSV-2 serostatus reported here merits further investigation.”