AIDS Acquired Immunodeficiency Syndrome (AIDS), is a kind of human viral disease (病毒病) that damages the immune system, weakening the body's ability to defend itself from infection and disease. Caused by the human immunodeficiency virus (HIV), AIDS leaves an infected person vulnerable to opportunistic infections. Such infections are harmless in healthy people, but in those whose immune systems have been greatly weakened, they can prove fatal. Although there is no cure for AIDS, new drugs are available that can lengthen the life spans and improve the quality of life of infected people. Infection with HIV does not necessarily mean that a person has AIDS. Some people who have HIV infection may not develop any of the clinical illnesses that define the disease of AIDS for ten years or more. Physicians prefer to use the term AIDS for cases where a person has reached the final, life threatening stage of H1V infection. AIDS was first identified in 1981 among homosexual (同性恋) men and drug users in New York and California. Shortly after its detection in the United States, evidence of AIDS epidemics (流行) grew among heterosexual (异性恋) men, women, and children in Africa. AIDS quickly developed into a worldwide epidemic, affecting virtually every nation. By 2002 an estimated 38.6 million adults and 3.2 million children worldwide were living with HIV infection or AIDS. The World Health Organization (WHO), a specialized agency of the United Nations (UN), estimates that from 1981 to the end of 2002 about 20 million people died as a result of AIDS. About 4.5 million of those who died were children under the age of 15. North America In the United States about 40,000 new HIV infections occur each year. More than 30 percent of these infectious occur in women, and 60 percent occur in ethnic minorities. In 2001 mere than 800,000 U.S. residents were infected with HIV, and more than 300,000 people were living with full-blown (全面的) AIDS. In Canada about 4,200 new HIV infectious occur each year. Nearly 25 percent of these infections occur in women. In 2002 about 55,000 Canadians were living with HIV infection and about 18,000 people were living with full-blown AIDS. The incidence of new cases of HW infections and AIDS deaths has significantly decreased in Canada and the United States since 1995. This decrease is attributed to the availability of new drug treatments and public health programs that target people most at risk for infection. But while the overall rate of HIV infection seems to be on a downturn (低迷时期), certain populations appear to be at greater risk for the disease. In the United States in 1987, Caucasians (白种人) accounted for 60 percent of AIDS cases and blacks and Hispanics only 39 percent. But by 2000 the trend had reversed: 26 percent of new eases were diagnosed in Caucasians and 73 percent in blacks and Hispanics. Likewise the number of female AIDS patients in the United States has increased significantly in recent years, from 7 percent of all AIDS cases in 1985 to 30 percent in 2000. In the United States, African American and Hispanic women accounted for 82 percent of AIDS cases among women in 2000. Europe In western Europe the first cases of AIDS were detected in the early 1980s, and by the late 1990s, at least 30,000 new HIV infections occurred each year. In 2002 about 570,000 western Europeans were HIV positive, and 25 percent of these cases were women. Before the dissolution (解散) of the Union of Soviet Socialist Republics (US.SR) in 1991, eastern Europe reported few HIV cases. But since 1995, HIV infection has spread rapidly in cities of several eastern European countries. The WHO estimates that the total number of HIV infections in this region may have risen from less than 30,000 in 1995 to about 1 million in 2002. Developing Nations While eases of AIDS have been reported in every nat