Opportunistic infections (OIs) are infections that take the opportunity of a person’s weakened immune system to manifest itself and cause grievous effects on that person. Common opportunistic infections seen in patients at late stage HIV disease ie. AIDS stage include:

Candidiasis (oral, esophageal or vaginal) Disseminated Tuberculosis Pneumocystis pneumonia (PCP) Cerebral toxoplasmosis Cryptococcal meningitis Cytomegalovirus (CMV) retinitis Kaposi’s sarcoma

Many people are HIV-positive but don't get sick for many years. As HIV disease continues, it slowly wears down the immune system and progresses to AIDS. AIDS is a condition in which the body's immune system breaks down and is unable to fight off certain infections, known as opportunistic infections and other illnesses that take advantage of a weakened immune system.