In fact, the distribution of AIDS cases, whether in the United States or elsewhere in the world, invariably mirrors the prevalence of HIV in a population (U.S. Bureau of the Census, 1994). In the United States, HIV first appeared in populations of homosexual men and injection drug users, a majority of whom are male (Curran et al., 1988). Because HIV is spread primarily through sex or by the exchange of HIV-contaminated needles during injection drug use, it is not surprising that a majority of U.S. AIDS cases have occurred in men.

Increasingly, however, women are becoming HIV-infected, usually through the exchange of HIV-contaminated needles or sex with an HIV-infected male (Vermund, 1993b; CDC, 1995a). As the number of HIV-infected women has risen, so too have the number of female AIDS cases. In the United States, the proportion of AIDS cases among women has increased from 7 percent in 1985 to 18 percent in 1994. AIDS is now the fourth leading cause of death among women aged 25 to 44 in the United States (CDC, 1994).

In Africa, HIV was first recognized in sexually active heterosexuals, and in some parts of Africa AIDS cases have occurred as frequently in women as in men (Quinn et al., 1986; Mann, 1992a). In Zambia, for example, the 29,734 AIDS cases reported to the WHO through October 20, 1993, were equally divided among males and females (WHO, 1995a,b).