Use of injectable progestin contraception and risk of STI among South African women.

OBJECTIVE

This study was conducted to determine the association between the use of injectable progestin contraception (IPC) and the risk of infection with Neisseria gonorrhoeae (GC), Chlamydia trachomatis (CT), bacterial vaginosis (BV) and Trichomonas vaginalis (TV) among women in South Africa.

METHODS

From August 1999 through May 2001, 643 HIV-1-negative women were recruited from family planning clinics in Orange Farm, South Africa. IPC [norethisterone enanthate (NET-EN) and depot medroxyprogesterone acetate (DMPA)] users and nonhormonal contraception users were recruited in approximately equal numbers. Eligible participants were seen at enrolment and on four follow-up visits over a 12-month period; 567 returned for at least one follow-up visit. Multivariable Poisson regression models with generalized estimating equations were used to compute the incidence rate ratios (IRRs) for infections with GC, CT, BV and TV by use of NET-EN or DMPA relative to nonuse during follow-up.

RESULTS

In multivariable models, the use of DMPA slightly increased the risk of infection with CT [IRR=1.24; 95% confidence interval (95% CI)=0.80-1.94] and GC (IRR=1.30; 95% CI=0.58-2.98), although these associations were not statistically significant. In contrast, DMPA appeared to be protective for TV (IRR=0.35; 95% CI=0.12-1.01), although this estimate was very imprecise. The use of both DMPA and NET-EN was associated with a decreased risk of BV.

CONCLUSIONS

The use of DMPA among women in this study population was associated with an increased - but not statistically significant - risk of cervical infection with chlamydia and gonorrhea, and a decreased risk of TV and BV. Given the inconsistencies and limitations of the data describing an increased risk of CT and GC with IPC use, the potential risk of sexually transmitted infections (STIs) must be balanced against the risk of unintended pregnancy and its health consequences, especially in developing countries. Women opting to use IPC should be counseled to use condoms to protect against STIs and HIV.