COMPARISON OF FEMALE TO MALE AND MALE TO FEMALE TRANSMISSION OF HIV IN 563 STABLE COUPLES

Objective - To identify risk factors for heterosexual transmission of HIV and to compare the efficiency of male to female and female to male transmission. Design - Cohort study of heterosexual couples. Regular partners of HIV infected subjects were tested and both members of the couples interviewed every six months. HIV prevalence in partners was a nalysed according to the characteristics of the couples. Setting - Nin e European countries. Subjects - 563 couples comprising 156 female ind ex patients with their 159 male partners and 400 male index patients w ith their 404 female partners. Partners reporting risk factors other t han sexual contacts with the index patient were excluded. Main outcome measures - HIV infection in partners and high risk sexual behaviour. Results - Overall, 19 (12%) male partners and 82 (20%) female partners were infected with HIV, suggesting that male to female transmission i s 1.9 (95% confidence interval 1.1 to 3.3) times more effective than f emale to male transmission. An advanced stage of HIV infection in the index patient (odds ratio 17.6; 4.9 to 62.7) and sexual contacts durin g menses (3.4; 1.0 to 11.1) increased the risk of female to male trans mission and stage of infection (2.7; 1.5 to 4.9), anal sex (5.1; 2.9 t o 8.9), and age of the female partner (3.9; 1.2 to 13.0 for age > 45 y ears) increased the risk of male to female transmission. None of the 2 4 partners who had used condoms systematically since the first sexual contact was infected. Conclusions - Several factors which potentiate t he risk of transmission through unprotected vaginal intercourse have b een identified. Knowledge of these factors could be helpful for counse lling patients infected with HIV and their sexual partners.