1. An illness caused by an organism that usually does not cause disease in a person with a normal immune system. People with advanced HIV infection suffer opportunistic infections of the lungs, brain, eyes, and other organs.
2. Opportunistic infections common in AIDS patients include Pneumocystis carinii pneumonia; Kaposi's sarcoma; shigellosis; histoplasmosis; other parasitic, viral, and fungal infections; and some types of cancers.