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Sex Transm Infect doi:10.1136/sti.2009.036731
  • Original Article

A comparison of four condom-use measures in predicting pregnancy, cervical STI and HIV incidence among Zimbabwean women

  1. Alexandra M Minnis*,
  2. Ariane van der Straten,
  3. Caitlin Gerdts,
  4. Nancy S Padian
  1. RTI International and University of California, United States
  1. Correspondence to: Alexandra Minnis, Women's Global Health Imperative, RTI International, 114 Sansome Street, Suite 500, San Francisco, CA, 94104, United States; aminnis{at}rti.org
  • Received 10 March 2009
  • Accepted 15 October 2009
  • Published Online First 1 November 2009

Abstract

Objective: To determine which condom-use measures best predict biological outcomes in STI/HIV prevention research.

Methods: In a prospective cohort study of 2,296 HIV negative Zimbabwean women aged 18-35 followed for up to two years, we compared four measures of condom use (use since last visit, use at last sex, frequency of use, and count of unprotected acts). We evaluated the performance of each in predicting incidence of pregnancy, cervical STIs (chlamydia/gonorrhea), and HIV.

Results: Over follow-up, 19.3% of women became pregnant; 10.3% acquired a cervical STI; and 6.9% acquired HIV infection. In multivariable analysis, all four condom-use measures were significantly associated with reduced pregnancy incidence; statistical tests-of-fit suggest that the frequency of use measure was most predictive. The time to pregnancy was longer for women who, in a typical month during the previous three months, reported always using condoms as compared with those who never used a condom (HR: 0.19, 95% CI: 0.14, 0.26). Among those women diagnosed with prevalent chlamydia/gonorrhea at study enrollment, three of the four reported condom use measures were associated with a non-significant but decreased risk of incident cervical STI. Reported condom use was associated with an increased risk for cervical STI among women without chlamydia/gonorrhea at enrollment. None of the condom-use measures were associated with HIV infection.

Conclusion: The frequency of reported condom use measure best predicted pregnancy incidence; however, we found no evidence for a clear “best” condom-use measure for use in STI/HIV prevention research in this population of Zimbabwean women.

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