through contaminated blood transfusions, 5 percent were partners of men in multiple risk groups, and 4 percent were partners of men in unidentified risk groups. Of the 85 women who had 0 to 200 sexual contacts with their infected partners, 13 percent were HIV positive; of the 65 women who had 201 to 2,170 sexual contacts with their infected partners, 37 percent were HIV positive.

With regard to the infectiousness of the seropositive partner, a higher rate of infection among the female partners of men in advanced clinical stages of HIV disease has been well documented (Laga et al., 1989). This is probably due to the fact that declining immune function enhances infectivity in an HIV-positive individual, and as such, bodily fluids such as blood and semen contain higher concentrations of HIV. One factor in this regard is a history of sexually transmitted diseases (CDC, 1987).

One of the more comprehensive studies of heterosexual transmission to examine the full range of risk behaviors was conducted by the Italian Study Group on HIV Heterosexual Transmission (Lazzarin et al., 1991). The sample included 368 women whose only potential exposure to HIV was having a male sex partner who was HIV positive, and 27.7 percent of these women were seropositive. The findings of the study documented risk duration, type and frequency of sexual intercourse, the man's infectiousness, and the woman's susceptibility as the key factors. With respect to risk duration, for example, women having a relationship with an infected male for 1 to 5 years had the highest prevalence of seropositivity, and a frequency of sexual intercourse more than twice a week was associated with a twofold increased risk of infection. Seropositive women reported anal intercourse twice as frequently as seronegative women, but condom use had a clear association with reduced rates of heterosexual transmission. In addition, infected women were more frequently those whose partners' disease had progressed to AIDS. Finally, seropositive women also reported histories of syphilis, genital warts, or genital herpes more so than seronegative women.

All of these studies document that, although the transmission of HIV from an infected male to a female partner is not always certain with any amount of exposure, considerable risk is always present. Such risk can increase dramatically depending on the type and frequency of the sexual contacts and the immunological state of the partners.

Female-to-male sexual transmission of HIV is supported by biological plausibility, equal numbers of male and female AIDS cases in African and Asian countries, case reports of males with no risk

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