Background:
Despite the importance of human immunodeficiency virus (HIV) transmission through heterosexual contact, the incidence of HIV infection in heterosexual cohorts has not been well studied, particularly in the developing world.

Objective:
To 1) determine the incidence of HIV infection in discordant heterosexual couples [couples in which one partner had HIV infection and the other did not] in Haiti and 2) assess risk factors for and methods of preventing HIV infection.

Design:
Prospective study.

Setting:
National Institute for Laboratory Research, Portau-Prince, Haiti.

Participants:
475 HIV-infected patients and their noninfected regular sex partners.

Measurements:
Patients and their partners were evaluated at 3- to 6-month intervals for HIV infection, sexually transmitted diseases, and sexual practices. The efficacy of counseling and provision of free condoms was also evaluated.

Results:
Among the 177 couples who remained sexually active during the prospective study period, 20 seroconversions to HIV positivity occurred, for an incidence rate of 5.4 per 100 person-years (95% CI, 5.16 to 5.64 per 100 person-years). Thirty-eight couples (21.5%) discontinued sexual activity during the study. Only 1 seroconversion occurred among the 42 sexually active couples (23.7% of the 177 sexually active couples) who always used condoms. In contrast, the incidence in sexually active couples who infrequently used or did not use condoms was 6.8 per 100 person-years (CI, 6.49 to 7.14 per 100 person-years).

Transmission of HIV was associated with genital ulcer disease, syphilis, and vaginal or penile discharge in the HIV-negative partner and with syphilis in the HIV-infected partner.

Conclusion:
Counseling and the provision of free condoms contributed to the institution of safe sex practices or abstinence in 45% of discordant heterosexual couples. However, 55% of couples reported that they continued to have unprotected sex, resulting in an incidence of HIV infection of 6.8 per 100 person-years.