AIDS stands for acquired immunodeficiency syndrome: AIDS is a life-threatening disease that results from severe damage to part of the body's cellular immune system—the defense system against opportunistic infections and some cancers. The disease is acquired (as opposed to genetic or hereditary) and presents a myriad of clinical manifestations (syndromes) that result from severe damage to the immune system. AIDS was first identified in 1981 among homosexual men in California and New York, and among illicit injected-drug abusers in New York City. After 1981, the numbers and types of AIDS patients increased rapidly; it was diagnosed in millions of persons throughout the world. In the United States alone, the Centers for Disease Control (CDC) estimated in 1996 that 1 million persons were HIV-positive and 223,000 were living with AIDS.

By 1996, injecting drug abusers accounted for 26 percent of cases among men, 70 percent of cases among women, and...