Definition of AIDS AIDS is defined as a disease, at least moderately predictive of defects in cell-meditated immunity, occurring in a person with no known cause for diminished resistance to that disease. Such diseases include Kaposi's Sarcoma, Pneumocystiscarnii pneumonia, and serious other opportunistic infections. After the discovery of HIV and the development of HIV-antibody test, the case definition of AIDS was updated to reflect the role of the virus in causing AIDS, but the scope of the definition remained almost the same. Being one of the most fatal viruses in the nation, AIDS (Acquired Immune deficiency