Acquired Immunodeficiency Syndrome (AIDS) and Human Immunodeficiency Virus (HIV) are not the same thing. AIDS and HIV are unquestionably related, yet different. HIV is the virus that causes AIDS. A person may test positive for the presence of HIV in his or her bloodstream, yet not have AIDS. An HIV-positive individual may be diagnosed with AIDS at some later point in time or not at all.

To understand how AIDS and HIV are related, it is necessary to understand how HIV infection works. Basically, HIV damages cells within the body’s immune system. The immune system is responsible for fighting off diseases and infections. As HIV does its work, more and more cells become damaged, and the immune system gradually loses its ability to ward off disease and infection.

HIV damages cells rather slowly. This is a major reason why making the distinction between AIDS and HIV is important. A person with HIV can appear and feel healthy for years before beginning to experience symptoms. An infected person may be completely unaware that he or she is positive for HIV. This is why testing is so important.

AIDS can be described as the final stage of infection with HIV. Once HIV has weakened an individual’s immune system beyond a certain point, his or her body becomes more vulnerable to infections. Infections that often affect those with AIDS include certain types of pneumonia and cancers. AIDS patients are also vulnerable to eye infections. Without the protection of the immune system, a person cannot fight off infections and could even die from a fairly common illness.

A key to the distinction between AIDS and HIV is the development of an AIDS defining illness. An AIDS defining illness is one that is very serious and opportunistic. Though AIDS defining illnesses can occur in individuals who are completely free of AIDS and HIV, they commonly, and often tragically, afflict those with AIDS. Such diseases include, but are not limited to, Kaposi's sarcoma, tuberculosis, cytomegalovirus, recurrent pneumonia, and wasting syndrome.

A doctor’s diagnosis is required to differentiate between AIDS and HIV infection. As a positive HIV test result does not carry with it the automatic diagnosis of AIDS, physicians use a range of clinical criteria in diagnosing AIDS. However, many individuals use the terms AIDS and HIV interchangeably, leading to confusion among those who do not know the difference.