Modes of Transmission
Researchers have isolated HIV from a number of body fluids, including blood, semen, saliva, tears, urine, cerebrospinal fluid, breast milk, and cervical and vaginal secretions. Strong evidence indicates, however, that HIV is transmitted only through three primary routes: sexual intercourse, whether vaginal or anal, with an infected individual; exposure to infected blood or blood products; and from an infected mother to her child before or during birth.
At least 97 percent of U.S. AIDS cases have been transmitted through one of these routes, with transmission by sex between men accounting for about 49 percent of the cases. Heterosexual transmission in the United States accounts for about 9 percent of cases but is rising; it is a significant mode of transmission in Africa and Asia. About 26 percent of AIDS cases occur in intravenous drug users exposed to HIV-infected blood through shared needles. Current practices of screening organ and blood donors and testing all donated blood and plasma for HIV antibodies have reduced the number of cumulative cases caused by transfusion to about 1 percent.
AIDS has become the leading cause of death for women between the ages of 20 and 40 in the major cities of North and South America, Western Europe, and sub-Saharan Africa, and it is spreading rapidly in Southeast Asia.
In the United States, AIDS has hit hardest among black and Hispanic women, who represent 17 percent of the female population but make up 78 percent of women with AIDS. AIDS is also having a devastating impact on infant mortality, since 91 percent of HIV-infected children under the age of 13 acquired HIV from their infected mothers. Between 24 and 33 percent of children born to infected women will develop the disease.
No scientific evidence supports transmission of HIV through ordinary nonsexual contact. Careful studies show that despite prolonged household contact with infected individuals, family members have not become infectedÑexcept through the routes described above. Health-care workers have been infected with HIV from exposure to contaminated blood or by accidentally sticking themselves with contaminated needles.