What is the difference between HIV and AIDS?

Cell infected with HIV, SEM
THOMAS DEERINCK, NCMIR/SCIENCE PHOTO LIBRARY / Getty Images

Decades have passed since HIV was first discovered, and people still use the terms HIV and AIDS interchangeably. Unfortunately, AIDS and HIV are not the same, and mixing up the terms can be very misleading.

The difference between HIV and AIDS is actually quite straightforward. HIV is a virus. AIDS is a definition. You cannot have AIDS without being infected with HIV. However, people can live long, healthy lives with HIV without ever developing AIDS. 

Defining HIV

HIV stands for "human immunodeficiency virus." In other words, it is a virus that infects a 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 a variety of specialized cells and proteins, such as antibodies. As a whole, the immune system works together to fight bacteria, viruses, and other agents that cause disease.

Diagnosing HIV

HIV is diagnosed through HIV testing. A person who has been infected with the virus is considered to be HIV positive. If there is no evidence of infection, they're considered to be HIV negative. It's possible for tests to be wrong in the case of new infections, but the definition of HIV of what it means to be HIV positive is relatively simple. Either you are infected with the virus or you aren't. Understanding AIDS is a bit more complex. 

Defining AIDS

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. If 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. When the immune system is made less effective in this way, a person is considered to have an acquired immune deficiency. That's the origin of the term AIDS.

Diagnosing AIDS in the Era of Opportunistic Infection

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:

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

AIDS can be diagnosed if someone is both HIV positive and has a specified opportunistic infection.

Defining and Diagnosing AIDS in the Modern Treatment Era

As HIV treatments have improved, opportunistic infections have become less common. Some people may live a long life with HIV without ever developing an opportunistic infection. So what does it mean to have AIDS today?

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 they must have one of the specific group of diseases that are designated as opportunistic infections OR numbers of specific types of cells in their immune system must drop below a certain level. That is why AIDS is considered a definition. It's not as simple as looking for a virus. AIDS requires a patient to fulfill several objective (and changing) criteria for diagnosis.

AIDS is not the necessary result of infection with a pathogen. It may or may not occur in someone with HIV. 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. 

HIV Doesn't Always Mean AIDS

Not everyone with HIV will develop HIV. In fact, as treatment improves, fewer and fewer HIV positive people will develop AIDS. That's because the virus can generally be kept under control with appropriate medication. When the virus is suppressed, people may never become immune deficient. They may never develop AIDS.

We talk about preventing HIV because it is a virus that can be transmitted. Transmission can be prevented through safe sex and other practices that protect people from exposure to potentially infected blood and bodily secretions. In contrast, discussions about preventing AIDS are really discussions about treating HIV. It is keeping the virus under control that stops the development of the syndrome.

A Word from Verywell

People can live with HIV for many years without developing AIDS or any symptoms of HIV infection. Highly effective treatment options are increasingly available. 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 of people with HIV. Treatment also reduces the likelihood that someone will pass the virus to a someone new.

The importance of early, appropriate treatment means that it's critical for anyone at risk to be regularly tested for HIV. Without testing, people can be infected for years without ever knowing it. Unfortunately, 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. However, HIV is not spread through casual contact.

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