Man-to-woman sexual transmission of the human immunodeficiency virus. Risk factors related to sexual behavior, man's infectiousness, and woman's susceptibility. Italian Study Group on HIV Heterosexual Transmission.

To investigate the risk factors for man-to-woman sexual transmission of the human immunodeficiency virus (HIV), we carried out a cross-sectional study of 368 women who were steady partners of HIV-infected men attending 16 Italian clinical centers. Information was collected from the medical records of the infected men and by direct interviews with the women. In a logistic regression analysis, the woman's awareness of her partner's seropositivity (odds ratio [OR], 0.2; 95% confidence interval [CI], 0.0 to 1.1), use of condoms (OR, 0.3; 95% CI, 0.1 to 1), and oral contraceptive use (OR, 0.5; 95% CI, 0.3 to 1.0) were negatively associated with transmission of the HIV infection. An increased risk was found in women having sexual intercourse more than twice a week (OR, 2.4; 95% CI, 1.2 to 4.9) and in women who had been sexually exposed to HIV for between 2 and 5 years (OR, 3.5; 95% CI, 1.8 to 6.7). The transmission rate was higher in couples who engaged in anal sex (OR, 2.8; 95% CI, 1.3 to 6.3); in women reporting vaginitis (OR, 4.9; 95% CI, 2.4 to 10.2) or genital warts (OR, 33.3; 95% CI, 4.5 to 244.1); and in those using intrauterine devices (OR, 3.1; 95% CI, 1.4 to 7.1). The risk for women was also associated with a CD4+ cell count lower than 400/mm3 in their partners. Knowledge of the HIV status of the partner led to increased condom use but did not induce a lower frequency of sexual intercourse or an avoidance of anal sex.