Human Immunodeficiency Virus (HIV)

Medically Reviewed on 6/30/2022

What is HIV?

  • HIV (human immunodeficiency virus) is a sexually transmitted virus that attacks the immune system. If it is not treated, it can lead to AIDS (acquired immunodeficiency syndrome). Currently, there is no cure for HIV. Once someone is infected, they have it for life, though with treatment, people with HIV can live long, healthy, fulfilling lives.

    Anyone can get HIV, regardless of gender, sexuality, race, nationality, age, or religion.

How is HIV transmitted? 

HIV is transmitted most commonly through sexual contact. It enters the body through mucous membranes via bodily fluids:

It can also be transmitted by sharing needles, syringes, or drug use equipment with someone who has the virus. Uncommonly, it can also be spread by contaminated blood products. Blood screening has made this risk very low.

HIV can also be transmitted from mother to infant during pregnancy, childbirth, or breastfeeding.

HIV is not transmitted by:

  • Hugging
  • Shaking hands
  • Sharing dishes or eating utensils or cups
  • Saliva, sweat or tears
  • Toilet seats
  • Sharing clothing
  • Mosquitos or other insects
  • Air or water

What are the stages of HIV?

There are three stages of HIV infection:

  • Acute HIV Infection - This stage is the earliest stage of HIV, and develops within 2 to 4 weeks after infection. HIV multiplies rapidly throughout the body, and is attacking and destroying CD4 cells, the helper cells of the immune system. During this stage, the following symptoms may appear:
  • It is important to note that these symptoms occur with many illnesses, and HIV can never be diagnosed based on symptoms.
  • Some people may have no symptoms, or they may be very mild.
  • HIV at this stage is very infectious.
  • Chronic HIV Infection - This stage is also called asymptomatic HIV. The virus is multiplying at a very low rate. Without treatment, this stage can last for ten years or longer, though it may advance to the next stage much more rapidly in some. With treatment, it may last decades. While it is still possible to transmit HIV to others during this stage, people who are on treatment and maintain an undetectable viral load have effectively no risk of transmitting HIV to an HIV-negative partner through sex.
  • AIDS - Acquired Immunodeficiency Syndrome - This is the final and most severe stage. HIV has damaged the immune system so badly and has left the body unable to fight off infections it otherwise would be able to. These are called opportunistic infections. People with AIDS have a CD4 count of less than 200 cells and/or they have certain opportunistic infections.
  • HIV at this stage is very infectious.


What is HIV? See Answer

How is HIV diagnosed?

HIV can be diagnosed through blood or saliva testing. There are three main types of HIV tests:

  • Antibody tests: These tests look for antibodies to HIV in the blood or saliva. Antibodies are proteins that the body produces in response to an infection. It can take up to 90 days for antibodies to become detectable after exposure to HIV.
  • Antigen/antibody tests: These tests look for both antibodies and antigens to HIV. Antigens are substances on the surface of the HIV virus. These tests can detect HIV earlier than antibody tests, but they are not as sensitive. These tests can be done at 4-6 weeks after exposure to HIV.
  • Nucleic acid tests (NATs): These tests look for the actual virus in the blood. NATs are the most sensitive HIV tests available, but they are also the most expensive.

How is HIV treated? 

HIV is treated with antiretroviral therapy (ART). ART is a combination of HIV medicines that work together to keep the virus from multiplying in the body. ART is not a cure for HIV, but it can help people with HIV live a long and healthy life.

ART is usually taken as a single pill once a day. There are many different types of ART available.

It is important to take ART as prescribed. If doses are missed, the virus can multiply and become resistant to treatment.

ART can also help to reduce the risk of transmitting HIV to others. If someone has an undetectable viral load, they are very unlikely to transmit the virus to their sexual partners.

How is HIV prevented? 

HIV can be prevented in a number of ways:

  • Abstinence: The most effective way to prevent HIV is to abstain from sex altogether. This means not having vaginal, anal, or oral sex.
  • Condoms: Condoms are very effective at preventing the transmission of HIV. When used correctly every time, condoms can reduce the risk of getting HIV by up to 99%.
  • PrEP: PrEP is a daily pill that can help prevent HIV infection. PrEP is highly effective when taken as prescribed, and it can be a great option for people who are at high risk of getting HIV.
  • PEP: PEP is a post-exposure prophylaxis medication that can be taken after HIV exposure. PEP is not as effective as PrEP, but it can still be effective if taken within 72 hours of exposure.
  • Getting tested: Getting tested for HIV is an important part of prevention. If people know their HIV status, they can take steps to protect themselves and others.

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Medically Reviewed on 6/30/2022
Branson, B.M., Handsfield, H.H., Lampe, M.A., et al. "Revised Recommendations for HIV Testing of Adults, Adolescents, and Pregnant Women in Health-Care Settings." MMWR 55 (2006): 1-17.

DHHS Panel on Antiretroviral Guidelines for Adults and Adolescents. "Guidelines for the Use of Antiretroviral Agents in HIV-1 Infected Adults and Adolescents." Washington D.C.: Department of Health and Human Services, 2020. <>.

Saag, M.S., R.T. Gandhi, J.F. Hoy, et al. "Antiretroviral Drugs for Treatment and Prevention of HIV Infection in Adults." JAMA 2020; ePub ahead of print.