There is a significant difference between HIV infection and AIDS. HIV infection refers to a person being infected with the HIV virus, but not yet reaching the stage of illness. At this time, the body's immune system is generally still normal, there are no other discomforts, and no opportunistic infections have occurred. This refers to HIV infection. AIDS, however, usually denotes the stage of illness onset, commonly featuring some opportunistic infections or opportunistic tumors, with many symptoms appearing. By testing CD4 cells, a diagnosis of AIDS is often made when CD4 cell counts are generally below two hundred.