Human Immunodeficiency Virus (HIV) is the virus that causes AIDS (Acquired Immune Deficiency Syndrome). Being HIV–positive or having HIV disease is not the same as having AIDS. Many people are diagnosed with HIV but may not get sick for many years. Once in a person's system, HIV begins to attack the immune system and for many who are HIV–positive, over a period of time, they can become ill with a number of conditions.
An HIV–positive person is diagnosed with AIDS when that person has developed certain opportunistic infections or other medical conditions such as a T–cell or CD4 (the most basic element of the immune system) count of less than 200. Only a physician can officially make the diagnosis that a person with HIV now has "AIDS". Generally an AIDS diagnosis occurs many years after infection.
HIV is the virus, AIDS is the disease and "HIV disease" is the most appropriate way to describe the continuum of HIV to AIDS. It is important to note that an AIDS diagnosis does not mean that an individual will soon die. While severe illness can develop, there are many medications available to help treat these. With good medical care it is possible for a person to maintain good health even after an AIDS diagnosis.