What Is AIDS?

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

Cell infected with HIV, SEM

Thomas Deerinck / Science Photo Library / Getty Images

But, even then, scientists understood that the route from infection to illness was not a straight line and that a clear definition of AIDS was needed to provide treaters with a road map of what to expect and how to intervene.

HIV stands for the human immunodeficiency virus, a virus that attacks causes disease by killing defensive immune cells and leaving the body vulnerable to an ever-widening host of infections that it would otherwise be able to control.

AIDS stands for acquired immunodeficiency syndrome, the most advanced stage of HIV infection in which the immune system is considered compromised. Without the immune defenses to ward off disease, a person with AIDS can develop severe and potentially life-threatening infections.

As straightforward as the definitions might seem, understanding when AIDS starts and what it actually means in terms of the risk of disease is a bit more complicated.


Understanding HIV and AIDS

What Is HIV?

HIV was first isolated in the early 1980s after public health officials in New York City and Los Angeles reported an outbreak of rare diseases among gay men—diseases that were generally not seen in young, healthy people.

Scientists soon discovered that the virus, initially dubbed HTLV-3, was able to rapidly kill defensive immune cells and, by doing so, leave a person susceptible to infectious organisms that usually do not cause disease. As scientists gained a greater understanding of how the virus worked, they renamed it HIV.

HIV is classified as a retrovirus, a rare group of viruses that uses RNA as its genetic material. When a retrovirus infects a host cell, it uses certain enzymes to turn its single-stranded RNA into double-stranded DNA. Once the DNA is inserted into the host cell's nucleus, it effectively "hijacks" the cell's genetic machinery and turns it into an HIV-producing factory.

HIV causes disease by targeting a type of white blood cell called a CD4 T-cell lymphocyte. While these "helper" cells do not kill disease-causing organisms like HIV, they are responsible for activating and coordinating the immune response (including disease-specific adaptive immunity).

How HIV Causes Disease

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

Defining AIDS

In the early days of the AIDS epidemic, scientists began to see patterns in how diseases developed in people with HIV. Because HIV was largely confined to gay men, the cluster of opportunistic infections was initially dubbed GRID (gay-related immunodeficiency). When it became clear that other groups could get infected through sex and injecting drug use, the syndrome was renamed AIDS.

Certainly, in the very early days of the epidemic, HIV and AIDS were largely considered synonymous given that the progression of the disease was rapid and there was not any form of treatment able to slow its progression.

But, even then, scientists understood that the route from infection to illness was not a straight line and that a clear definition of AIDS was needed to provide treaters with a road map of what to expect and how to intervene.

As epidemiological data was compiled, it became clear that the bulk of serious opportunistic infections occurred when the number of CD4 T-cells dropped below 200 cells per cubic millimeter (cells/mm3). By contrast, a normal CD4 count is between 500 and 1,200 (or higher).

However, at the same time, there were plenty of people with CD4 counts above 200 who developed potentially life-threatening infections. This questioned whether a definition focused purely on the CD4 count was sufficient.

In response, the Centers for Disease Control and Prevention (CDC) issued a definition of AIDS that largely remains intact today.

CDC Definition of AIDS

According to the 2014 CDC definition, AIDS is diagnosed when:

List of AID-Defining Conditions

Based on epidemiological data, the CDC issued the first list of AIDS-defining conditions in 1987. That list was expanded in 1994 and then again in 2008, in part to include severe opportunistic commonly seen in children with HIV.

Today, the CDC lists 27 different AIDS-defining conditions in people with HIV:

AIDS and Death

In the 1980s and into the early 1990s, an AIDS diagnosis was considered by many to be a death sentence. It was only with the introduction of highly active antiretroviral therapy (HAART) in 1996 that the outlook changed. With this new form of combination therapy, scientists were able to 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% within the span of three years.

Today, people with HIV who are diagnosed and treated early can expect to live normal to near-normal life expectancies.

Even people clinically diagnosed with AIDS can enjoy longer, healthier lives once antiretroviral treatment is started. (With that said, the lower your CD4 count is at the start of therapy, the less likely you will be to achieve complete immune recovery.)

Today, people living with HIV are more likely to die of non-HIV-related diseases, including cancers, than HIV-related ones⁠—many of which occur 10 to 15 years before people in the general population. Even so, antiretroviral therapy can cut the risk of both HIV- and non-HIV-related illness by half if started early (ideally before the CD4 count dips below 500).

How the Definition Changed

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.

Back in the 1980s and early-1990s, the CDC definition of AIDS was used to establish when a person was eligible for Social Security disability and other forms of financial or medical assistance. Because an AIDS diagnosis was still associated with a high risk of death, having a CD4 count of 200 was often enough to establish a person as permanently disabled.

The same criteria would not apply today. Because HIV is now considered a chronically managed condition, people who meet the definition of AIDS will need to undergo a case-by-case evaluation to determine if they are, in fact, disabled under the terms of the law.

At the same time, doctors are using the term "AIDS" less and less today—in part because of the fluidity of the definition but also because the prognosis for many AIDS-related conditions has improved dramatically since the time of the CDC definition. If anything, the term is used more for surveillance purposes than anything else.

On top of this, "AIDS" remains a highly stigmatizing term, and, in its place, many doctors and advocates prefer the term "advanced HIV infection" when describing the stage of the disease.

AIDS Prevention

Antiretroviral therapy is the one intervention that can halt disease progression and reduce the risk of HIV-associated illness in people with HIV. The drugs used today are not only more effective but also have fewer side effects and are less prone to early drug resistance. Some combination therapies have even been formulated to allow once-daily, single-pill dosing.

But, the pills only work if you take them. And, in the United States, this has become a far greater challenge than many people realize.

Of the roughly 1.2 million people living with HIV in the United States, only 66% have received HIV-specific care and only 54% have achieved complete viral suppression while on treatment. This leaves nearly a half million people vulnerable to otherwise avoidable illnesses.

While stigma plays a key role in these statistics, the lack of access to quality healthcare and misconceptions about HIV and HIV therapy continue to drive people away from highly effective, life-saving treatment.

Improvement in public health messaging—as well as advances in HIV treatment—hope to reverse these trends. This includes the development of simpler therapies like Cabenuva, an injectable combination drug approved in 2021 that only requires once-monthly dosing.

Other interventions, like HIV pre-exposure prophylaxis (PrEP), can reduce a person's risk of getting HIV by up to 99% if taken as prescribed. Advances like these can further reduce the fear surrounding HIV and may one day resign the term "AIDS" to the history books.

A Word From Verywell

HIV is not the same disease it was even 15 years ago. With appropriate treatment, people with HIV are at far lower risk of ever developing AIDS-related illnesses. Not only can they enjoy long, healthy lives, but they can even explore pregnancy and parenthood.

And, the benefits of treatment extend well beyond the person living with HIV. By achieving and sustaining an undetectable viral load, the likelihood of infecting others is reduced to zero. In short, by protecting your good health with consistent antiretroviral therapy, you also protect those around you.

Frequently Asked Questions

  • What is HIV?

    HIV is the human immunodeficiency virus. It causes disease by killing immune cells, called CD4 T-cells, that help triggers the immune response. When enough of these cells are killed, a person can become immune deficient and get opportunistic infections.

  • What is AIDS?

    AIDS stands for acquired immunodeficiency syndrome. It is the most advanced stage of HIV infection, defined as either having a CD4 count under 200 or specific "AIDS-defining" opportunistic infections.

  • How is HIV diagnosed?

    HIV is diagnosed with a blood test that is able to detect antibodies produced by the immune system in response to the virus. There are traditional in-office tests as well as rapid tests and even 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' life cycle. By blocking viral replication, the virus is suppressed to undetectable levels where it can do little harm.

  • How many people die of AIDS?

    There are around 38 million people living with HIV worldwide, and, 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.

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