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HIV is not transmitted by casual contact; transmission requires a direct exchange of body fluids, such as blood or blood products, breast milk, semen, or vaginal secretions, most commonly as a result of sexual activity or the sharing of needles among drug users. Such a transmission may also occur from mother to baby during pregnancy or at birth. Saliva, tears, urine, feces, and sweat do not appear to transmit the virus.
In 2001 it was estimated that 36 million people were infected with HIV worldwide, the great majority in Third World countries; nearly 22 million had died from AIDS. The disease in sub-Saharan Africa, which has been especially hard hit, in the main has been transmitted heterosexually and has been exacerbated by civil wars and refugee problems and less restrictive local mores with regard to sex. Some 25 million people were infected with HIV in this region. The estimated number of children orphaned by AIDS in sub-Saharan Africa was more than 10 million. The epidemic also has begun to manifest itself in Asia (especially in India, China, Myanmar, Thailand, and Cambodia) and Latin America.
In the United States, the demographics of AIDS have changed over time. In the 1980s it was seen mainly in homosexual and bisexual men and was one of the spurs to the gay-rights movement, as activists lobbied for research and treatment monies and began education and prevention programs. Also in the early years, before careful screening of blood products was deemed necessary, the virus was contracted by an estimated 9,000 hemophiliacs (see hemophilia), and a small number of people were infected by surgical or emergency blood transfusions. Before long, however, the majority of new HIV infections were seen in drug users who contracted the disease from shared needles or unprotected sex. A large proportion of infected women are drug users or partners of drug users. Nearly a third of the infants born to HIV-infected women are infected with the virus. (Some of these infants test positive for AIDS only because of the mother's antibodies and later test negative.)
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