Male-to-female transmission of human immunodeficiency virus.

Ninety-seven female sexual partners of 93 men infected with human immunodeficiency virus were studied. All of the women had sexual contact within the year before their partner had been diagnosed as having acquired immunodeficiency syndrome or was found to have a positive reaction on the human immunodeficiency virus serologic test. Fifty-seven percent were the partners of bisexual men. Overall, 23% of the women were infected (95% confidence interval, 15% to 32%). The total number of exposures to the index case (sexual contacts with ejaculation) and the specific practice of anal intercourse, also with the infected partner, were associated with transmission. Neither condom use, total number of sexual partners since 1978, nor lifetime number of sexually transmitted diseases was associated with infection.