AIDS Definition and Characterization

Man holding HIV medication cocktail, close-up
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Acquired immunodeficiency syndrome, Advanced HIV (human immunodeficiency virus) infection

Medical Specialties:

Internal medicine, Family medicine, Infectious disease

Clinical Definition:

Acquired immune deficiency syndrome, most commonly called AIDS, is a serious infection caused by the human immunodeficiency virus or HIV. The body cannot get rid of HIV. There are treatments but there is still no cure for this disease.

The virus is transmitted when an infected person's bodily fluids, such as blood, semen, vaginal fluids or breast milk, enter the blood stream of another person. Among the common routes of infection are sharing a needle to take drugs or having sex with a person infected with the virus.

In Our Own Words:

AIDS, or acquired immune deficiency syndrome, is the later stage of infection with HIV, the human immunodeficiency virus. The immune system is so badly damaged (low CD4 cells or T cells) that it becomes vulnerable to infections and to infection-related cancers. Those with AIDS need medical treatment to avoid dying of the infection and its complications. Testing is advised if HIV is suspected, since many people infected do not suffer any symptoms for 10 years or longer.

More Information About AIDS

In 1981, AIDS was first identified in the United States among several homosexual men living in both Los Angeles and New York City.

These men, who had been previously healthy, came down with Pneumocystis jiroveci (formerly P. carinii) pneumonia and Kaposi’s sarcoma (KS), both AIDS-defining opportunistic infections otherwise rarely seen. Shortly thereafter, AIDS was recognized in various other patient populations, including men and women who used intravenous drugs, female sexual partners of men with AIDS, infants born to mothers with AIDS, people who received infected blood transfusions and so forth.

By the mid-1980s, AIDS was a bona fide global pandemic. Fortunately, this explosion in disease incidence was matched by a concomitant explosion in our appreciation of the virology, pathogenesis and treatment of HIV, the virus that causes AIDS. Nowadays, we have very effective treatment for infection with this virus, such as combined antiretroviral therapy as well as treatment and prophylaxis for associated opportunistic infections. (Opportunistic infections affect people with compromised immune systems like those with AIDS.) A person with HIV who vigilantly takes her medications and is closely monitored by her physician can expect to live a long and healthful life. In sum, a diagnosis with HIV is no longer nearly as lethal as it once was.

It should be noted that HIV and AIDS are not synonymous. Specifically, there are 5 stages of HIV infection (0, 1, 2, 3 and unknown), and AIDS is advanced HIV infection (stage 3). To be diagnosed with AIDS or stage 3 HIV infection, a person must either have a really low CD4 T+ lymphocyte count or develop an AIDS-defining illness, such as Mycobacterium avium complex, progressive multifocal leukoencephalopathy as well as the aforementioned Kaposi's sarcoma or Pneumocystis jiroveci.

In other words, only really sick people with HIV have AIDS, and many otherwise healthy people receiving proper treatment harbor the HIV virus without exhibiting symptoms.


The Cleveland Clinic. "HIV/AIDS." Diseases & Conditions. Jan. 2010. 

Centers for Disease Control and Prevention. "What is HIV?" A-Z Topics. May 2013.

The Cleveland Clinic. “AIDS and Women” 2011 "What is AIDS?" 2011. 

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