Man-to-woman sexual transmission of the human immunodeficiency virus. Risk factors related to sexual behaviour, man's infectiousness, and woman's susceptibility

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.