What is the difference between HIV and AIDS?

Question: What is the difference between HIV and AIDS?

Answer: The quick answer is that the difference between HIV and AIDS is that HIV is a virus and AIDS is a definition.

What does HIV stand for?

HIV stands for "human immunodeficiency virus." In other words, it is a virus that infects human being and leads to problems with their immune system. The immune system is the body's system for fighting disease.

It is made up of several types of cells that. Working together with specialized proteins such as antibodies, these cells fight bacteria, viruses, and other agents that cause disease.


Understanding what it means to be HIV positive is relatively simple. Either you are infected with the virus or you aren't. However, understanding AIDS is a bit more complex. 

AIDS stands for "Acquired Immune Deficiency Syndrome." The diagnosis of AIDS is a way of describing a whole group of symptoms and diseases associated with the damage HIV does to the immune system. As an untreated HIV infection progresses, there is ongoing damage to immune defense cells. As this happens, the body becomes increasingly less able to fight off infections. This means that individuals with advanced HIV disease are susceptible to infections that don't show up in people with healthy immune systems. In fact, HIV and AIDS were initially recognized because of outbreaks of rare diseases and cancers that had not previously been seen in large numbers in the U.S.

Such infections are known as opportunistic infections because they take advantage of the weakened ability of an HIV positive individual to fight off disease. In other words, they are opportunistic. Some diseases considered to be opportunistic infections for the purpose of an AIDS diagnosis include:

  • Candidasis (yeast infections) of the throat and lungs
  • Invasive cervical cancer
  • Fungal infections caused by Cryptococcus or Coccidioides
  • HIV related brain infections
  • Kaposi's sarcoma

As HIV treatments have improved, opportunistic infections have become less common. Some people may live a lifetime with HIV without ever developing an opportunistic infection. So what is AIDS?

A person is said to have AIDS, as opposed to simply being HIV positive, when two things are true. First of all, they must have an HIV infection. Second, either the numbers of specific types of cells in their immune system must drop below a certain level or they must develop one of the specific group of diseases that are designated as opportunistic infections. That is why AIDS is considered a definition. It requires a patient to fulfill several objective criteria for diagnosis but is not the necessary result of infection with a pathogen. In contrast, HIV infection is sufficient for an HIV diagnosis. That's true whether or not someone has any symptoms or negative effects from the virus.


It is important to know that a person can live with HIV for many years without developing AIDS or any symptoms of HIV infection. In fact, highly effective treatment options are increasingly available. Therefore, many people with HIV live long, healthy lives without any signs of immune system dysfunction. However, appropriate treatment is essential for long-term health and well-being for people with HIV. That is why it is important to be regularly tested for the virus. Even if a person does not know they are infected, they can still transmit the virus to other people through unprotected sex. They can also transmit HIV through other risky behaviors that directly expose other people to their blood, semen, breast milk, and other potentially infectious bodily fluids. HIV is not spread through casual contact.

Pitchenik AE, Fischl MA, Dickinson GM, Becker DM, Fournier AM, O'Connell MT, Colton RM, Spira TJ. Opportunistic infections and Kaposi's sarcoma among Haitians: evidence of a new acquired immunodeficiency state. Ann Intern Med. 1983 Mar;98(3):277-84.

Schroff RW, Gottlieb MS, Prince HE, Chai LL, Fahey JL. Immunological studies of homosexual men with immunodeficiency and Kaposi's sarcoma. Clin Immunol Immunopathol. 1983 Jun;27(3):300-14.

What is AIDS? from the CDC. Accessed at www.cdc.gov/hiv/resources/qa/qa2.htm

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