HIV is the shortened term for human immunodeficiency virus. It belongs to a group of viruses called retroviruses. Retroviruses infect immune cells in the body depleting the body’s defense system against disease. These cells are known as T-cells or CD4 cells. Acquired immunodeficiency syndrome (AIDS) is a clinical disease diagnosed when HIV-infected persons are depleted of CD4 cells to a serum level of less than 200. When the body’s CD4 levels are this low, opportunistic infections or infections that would otherwise be destroyed by T-cells, are able to bypass the body’s defense mechanisms and cause disease. Treatments for HIV have drastically reduced the number of deaths from HIV/AIDS infection.