What Is AIDS?

A chronic and potentially life-threatening disease caused by HIV infection

Acquired immunodeficiency syndrome (AIDS) is the most advanced stage of human immunodeficiency virus (HIV) infection. At this point, the virus has infected and killed so many immune cells that the immune system is severely impaired.

Without defenses to ward off disease, a person with AIDS can develop severe and potentially life-threatening infections.

AIDS does not occur in everyone with HIV, but it can if HIV is left untreated.

This article takes a closer look at how HIV causes AIDS and the conditions and risks associated with this late stage of infection. It also explains how to avoid AIDS if you or a loved one are diagnosed with HIV.


Understanding HIV and AIDS

HIV: The Virus That Causes AIDS

HIV causes disease by targeting a type of white blood cell called a CD4 T cell. These are the cells responsible for activating the immune response, your body's defensive attack against things can cause it harm.

They also play a role in adaptive immunity, which is the body's targeted response to a specific invader, like HIV.

HIV is classified as a retrovirus, a rare type of virus that is able to insert its genetic material into the cells it infects. By doing so, the virus can "hijack" a cell's genetic machinery and turn it into an HIV-producing factory.

As HIV targets more CD4 T cells, the body becomes less able to mount an immune defense. When this happens, infections that the immune system would otherwise be able to control can cause disease. These are referred to as opportunistic infections.


HIV is a virus that causes disease by infecting immune cells, called CD4 T-cells, that activate the body's immune defenses. As more and more of these cells are killed, the body becomes less and less able to defend itself against infection. If left untreated, HIV will progress to AIDS.

When AIDS Is Diagnosed

In the past, HIV and AIDS were largely considered synonymous because the progression of the disease was rapid and there was no treatment to slow its progression.

However, the route from infection to illness is not a straight line, and there are definitions that distinguish HIV infection from AIDS.

The bulk of serious opportunistic infections occurs when the number of CD4 T cells drops below 200 cells per cubic millimeter (cells/mm3). By contrast, a normal CD4 count is between 500 and 1,200 (or higher).

There are also people with CD4 counts above 200 who develop potentially life-threatening infections.

The Centers for Disease Control and Prevention (CDC) issued a revised definition of AIDS in 2014 that largely remains intact today. According to the CDC, AIDS is diagnosed when:


AIDS is diagnosed either when a person's CD4 count drops below 200 or the person gets one of 27 different AIDS-defining conditions classified by the CDC.

List of AIDS-Defining Conditions

An AIDS-defining illness is one that is rarely seen outside of the context of advanced HIV infection.

The CDC lists 27 different AIDS-defining conditions in people with HIV:

Type  Condition  Special Criteria
Bacterial Bacterial infections Multiple or recurrent of any sort
  Mycobacterium avium complex   
  Other Mycobacterium species Spread beyond the lungs
  Salmonella septicemia Recurrent
Cancer Burkitt lymphoma
Cervical cancer Spread beyond the cervix
  Immunoblastic lymphoma  
  Kaposi's sarcoma  
  Primary lymphoma of the brain   
Fungal Candidiasis ("thrush") Involving the bronchi, trachea, esophagus, or lungs
  Cryptococcosis Spread beyond the lungs
Cryptosporidiosis Involving the intestines for more than one month
  Cytomegalovirus Involving organs other than the liver, spleen, or lymph nodes
  Cytomegalovirus retinitis Occurring with vision loss
  Histoplasmosis Spread beyond the lungs
  Pneumocystis pneumonia   
  Toxoplasmosis of the brain  
Viral Herpes simplex virus Lasting longer than a month or appearing in an area other than the skin (such as the esophagus or lungs)
Progressive multifocal leukoencephalopathy 
Other AIDS wasting syndrome 
HIV encephalopathy (AIDS dementia)
Lymphoid interstitial pneumonia
Pneumonia Recurrent of any sort

Treatment's Impact on Life Expectancy

In the past, an AIDS diagnosis was considered by many to be a death sentence. With the introduction of highly active antiretroviral therapy (HAART) in 1996, that outlook changed. This form of combination therapy can fully suppress the virus and slow disease progression.

During the height of the epidemic in the United States, HIV was the eighth leading cause of death overall. By the mid-1990s, it accounted for 23% of deaths among men ages 25 to 44 and 11% of deaths among women of the same age group.

By 1995, the HIV mortality rate had peaked to its highest level ever, killing nearly 50,000 U.S. citizens and residents. With the introduction of HAART, now referred to simply as antiretroviral therapy, the death rate plummeted by more than 50% in three years.

People with HIV who are diagnosed and treated early can expect to live normal to near-normal life expectancies. Without treatment, people diagnosed with AIDS survive for an average of two years.

Even people clinically diagnosed with AIDS can benefit from antiretroviral treatment. With that said, the lower your CD4 count is at the start of therapy, the less likely you will be to achieve immune recovery.

Today, people with HIV are more likely to die of cancer than from infections. Even so, antiretroviral therapy can cut the risk of cancer and infections by half if started early (ideally before the CD4 count dips below 500).


While the impact of this therapy cannot be overstated, it's also important to note that such outcomes are only applicable to those for whom these drugs are within reach. Some groups are more affected than others.

According to a report from the CDC, in 2019, 71% of White people with known HIV were virally suppressed. That number dropped to 65% and 61% for Hispanic/Latinx and Black peers, respectively.


Without treatment, people diagnosed with AIDS survive for an average of two years. By contrast, if HIV is diagnosed and treated early, people can live as long as those without HIV or close to it.

Use of the Term "AIDS"

Since the last revision of the list of AIDS-defining conditions was issued in 2008, the CDC definition of AIDS has remained largely unchanged. What has changed is how the definition is used.

In the past, the CDC's definition of AIDS was used to establish eligibility for Social Security disability and other forms of financial or medical assistance. Because an AIDS diagnosis was associated with a high risk of death, having a CD4 count of 200 was often enough to establish permanent disability.

The same criteria do not apply today. Because HIV is now considered a chronically managed condition (long-lasting, but able to be treated), people who meet the definition of AIDS need to undergo a case-by-case evaluation to determine if they are disabled under the terms of the law.

Healthcare providers are using the term "AIDS" less today—in part because the prognosis for many AIDS-related conditions has improved.

Furthermore, AIDS remains a highly stigmatized term, and, in its place, many healthcare providers and advocates prefer the term "advanced HIV infection" when describing the disease stage.


When the definition of AIDS was first issued, it was used in part to ensure that people who were nearing the end of their lives had access to Social Security disability. That concern no longer applies today given that people treated for HIV can live long, healthy lives.

AIDS Prevention

Antiretroviral therapy is the one intervention that can halt disease progression and reduce the risk of HIV-associated illnesses in people with HIV.

The medications used to treat HIV require that you take them consistently. For the majority of drugs used to treat the disease, this means taking one or more pills every day.

In 2021, a new once-monthly injectable therapy called Cabenuva (cabotegravir + rilpivirine) was approved for use in the United States. It was later approved for every-two-month dosing. The new form of treatment, which requires two separate injections every month or every two months, is able to suppress the virus as effectively as taking oral HIV drugs every day.

Of the roughly 1.2 million people living with HIV in the United States, only 66% receive HIV-specific care and less than 60% have achieved complete viral suppression while on treatment. This leaves nearly a half million people vulnerable to otherwise avoidable illnesses.


If you have HIV, the only way to avoid getting AIDS is to start antiretroviral therapy. Most therapies are taken once daily, but a new injectable therapy called Cabenuva only requires two separate injections once per month or every other month.


AIDS is the most advanced stage of HIV infection. It occurs when the virus severely compromises the body's immune defenses, leaving the body vulnerable to an ever-widening range of potentially life-threatening infections.

AIDS is diagnosed either when a person's CD4 count drop below 200 or they get one of 27 different AIDS-defining conditions. AID-defining conditions are illnesses that rarely occur outside of people with AIDS.

If left untreated, people with AIDS will usually die within two years of their diagnosis. By contrast, people diagnosed and treated early for HIV can live a long, healthy lives.

Frequently Asked Questions

  • How is HIV diagnosed?

    HIV is diagnosed with a blood test that detects antibodies produced by the immune system in response to the virus. There are in-office tests, rapid tests, and at-home HIV tests.

  • How is HIV treated?

    HIV is treated with antiretroviral therapy. Antiretroviral therapy involves a combination of two or more drugs that block specific stages in the virus's life cycle. By blocking viral replication, the virus is suppressed to undetectable levels, at which it can do little harm.

  • How many people die of AIDS?

    There are around 38 million people living with HIV worldwide. In 2019, nearly 700,000 died as a result of HIV-related complications. In the United States, around 5,000 deaths were attributed to HIV in 2018.

24 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Selik RM, Mokotoff ED, Branson B, Owen SM, Whitmore S, Hall HI. Revised surveillance case definition of HIV infection -- United States. Morbid Mortal Weekly Rep MMWR.

  2. Naif HM. Pathogenesis of HIV infection. Infect Dis Rep. 2013;5(Suppl 1):e6. doi:10.4081/idr.2013.s1.e6

  3. Justiz AA, Naik R. HIV-1 associated opportunistic infections. In: StatPearls [Internet].

  4. Battistini Garcia SA, Guzman N. Acquired immune deficiency syndrome. In: StatPearls [Internet].

  5. MedlinePlus. CD4 lymphocyte count.

  6. Centers for Disease Control and Prevention. Appendix A: AIDS-defining conditions. Morbid Mortal Weekly Rep MMWR.

  7. Tseng A, Seet J, Phillips EJ. The evolution of three decades of antiretroviral therapy: challenges, triumphs and the promise of the future. Br J Clin Pharmacol. 2015;79(2):182-94. doi:10.1111/bcp.12403

  8. Centers for Disease Control and Prevention. Updated: mortality attributable to HIV infection among persons aged 25-44 -- United States. Morbid Mortal Weekly Rep MMWR.

  9. Brady MT, Oleske JM, Williams PL, et al. Declines in mortality rates and changes in causes of death in HIV-1-infected children during the HAART eraJ Acquir Immune Defic Syndr. 2010;53(1):86-94. doi:10.1097/QAI.0b013e3181b9869f

  10. Marcus JL, Chao CR, Leyden WA, et al. Narrowing the gap in life expectancy between HIV-infected and HIV-uninfected individuals with access to careJ Acquir Immun Defic. 2016;73(1):39-46. doi:10.1097/QAI.0000000000001014

  11. Poorlajal J, Hooshmand E, Mahjub H, Esmailnasab N, Jenabi E. Survival rate of AIDS disease and mortality in HIV-infected patients: a meta-analysis. Public Health. 2016;139:3-12. doi:10.1016/j.puhe.2016.05.004

  12. Darraj M, Shafer LA, Chan S, Kasper K, Keynan Y. Rapid CD4 decline prior to antiretroviral therapy predicts subsequent failure to reconstitute despite HIV viral suppression. J Infect Public Health. 2018;11(2):265-9. doi:10.1016/j.jiph.2017.08.001

  13. Chao C, Leyden W, Xu L, et al. Exposure to antiretroviral therapy and risk of cancer in HIV-infected personsAIDS. 2012;26(17):2223-31. doi:10.1097/QAD.0b013e32835935b3

  14. INSIGHT START Study Group, Lungren JD, Babiker AG, Gordin F, et al. Initiation of antiretroviral therapy in early asymptomatic HIV infectionN Engl J Med. 2015;373(9):795-807. doi:10.1056/NEJMoa1506816

  15. Centers for Disease Control and Prevention. Monitoring selected national HIV prevention and care objectives by using HIV surveillance data—United States and 6 dependent areas, 2019HIV Surveillance Supplemental Report 2021;26(No.2).

  16. Social Security Administration. Providing medical evidence for individuals with human immunodeficiency virus (HIV) infection.

  17. POZ Magazine. Is it time for an end of 'AIDS'?

  18. GSKPro.com. Highlights of prescribing information: CABENUVA (cabotegravir extended-release injectable suspension; rilpivirine extended-release injectable suspension).

  19. Food and Drug Administration. FDA approves first extended-release, injectable drug regimen for adults living with HIV.

  20. HIV.gov. What is the HIV care continuum?

  21. Centers for Disease Control and Prevention. Types of HIV tests.

  22. Department of Health and Human Services. Guidelines for the use of antiretroviral agents in HIV-1-infected adults and adolescents.

  23. UNAIDS. Global HIV & AIDS statistics — fact sheet.

  24. Centers for Disease Control and Prevention. AIDS and HIV.

By Elizabeth Boskey, PhD
Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.