
Acquired Immunodeficiency Syndrome (AIDS) is the most severe stage of the infection caused by the Human Immunodeficiency Virus (HIV). People always develop an HIV infection first. If left untreated, the virus damages your immune system, and you develop AIDS.
Two measurements help determine the severity of your HIV infection: your viral load — the amount of virus in your blood — and your level of CD4 immune cells. These cells help your body fight off infections and are targeted by the virus.
The higher your viral load and the lower your CD4 count, the closer you progress from the early stages of HIV infection to AIDS.
What is HIV?
The human immunodeficiency virus causes a deadly infection. Researchers believe it was most likely introduced to humans through contact with the blood of chimpanzees with the simian immunodeficiency virus (SIV). The virus takes up permanent residence in your body and weakens your immune system over time, eventually leaving you susceptible to often-fatal infections.
The first case of HIV was officially diagnosed in the United States in 1981, but the virus has been present in the country from at least mid-to late-1970.
The World Health Organization (WHO) estimates over 37 million people worldwide lived with HIV in 2020. There were also over one million new global infections in that year alone.
These new cases are caused by the virus spreading from person to person. It can spread in several different bodily fluids, including:
- Blood
- Semen
- Pre-seminal fluid
- Vaginal fluid
- Rectal fluid
- Breast Milk
If you’re pregnant, there’s also a chance that you can pass the infection to your child.
Currently, there’s no cure for HIV. But there are very effective ways to prevent initial infection and AIDS.
What are the stages of HIV infection?
The United States Centers for Disease Control and Prevention (CDC) divides HIV into three stages:
- Stage 1: Acute HIV infection. It sets in around two to four weeks after initial contact with the virus.
- Stage 2: Chronic HIV infection. It sets in weeks to months after acute infection.
- Stage 3: More commonly known as AIDS. If left untreated, it usually doesn’t begin until around 10 years after entering stage two.
The WHO divides HIV into four levels of infection based on CD4 counts and the corresponding amount of damage to your immune system. These stages and their cut-offs are:
- No significant immunosuppression: CD4 counts are in a relatively normal range, at least greater than or equal to 500 cells/mm3 — a value corresponding to stage one in the CDC’s classification.
- Mild immunosuppression: CD4 counts have dropped between 350 to 499 cells/mm3.
- Advanced immunosuppression: CD4 levels are between 200 and 349 cells/mm3.
- Severe immunosuppression: CD4 count is below 200 cells/mm3, and you’ve officially transitioned from the CDC’s stage two into stage three, AIDS.
Everyone will progress from one stage to the next at slightly different rates. The average untreated disease takes just over 10 years to become AIDS. People tend to survive for around three years after the disease has advanced to this final stage.
Can you prevent AIDS if you have HIV?
The modern treatment for HIV is called antiretroviral therapy (ART). Used consistently, it’s highly effective at maintaining low enough viral loads to delay progression for many decades. In fact, some people may never develop AIDS in their lifetime.
The goal of ART is to reduce your viral load so that its presence is undetectable. When this is the case, you’re unlikely to transmit the virus to another person, and the destruction of your immune system dramatically slows.
Although not a cure, this treatment can lead to much longer and healthier lives for people diagnosed with HIV and is recommended at any stage of the disease.
What are the differences in HIV and AIDS symptoms?
In stage one of an HIV infection, you have a very high viral load and are likely to experience several flu-like symptoms, including:
You may not have any symptoms at all during stage two. At this stage, your viral load is stable at relatively low levels, and you’re less likely to transmit the disease to someone else.
Both symptoms and transmission are more likely when HIV progresses to AIDS. Now your immune system isn’t strong enough to fight off a class of infections called opportunistic infections (OIs) as well as certain cancers.
Opportunistic infections are only dangerous to people with compromised immune systems and are not commonly seen in otherwise-healthy people. Examples of OIs and cancers that are common in people with AIDS include:
- Fungal infections like those caused by the fungi Candida and Coccidioides
- Parasitic infections like those caused by Cryptosporidium or Cystoisospora belli
- Additional viral infections, including the Herpes Simplex Virus (HSV) or Cytomegalovirus (CMV)
- Invasive cervical cancer
- Lymphoma
Each of these OIs and cancers come with specific symptoms. In people with AIDS, these conditions, and their complications, can easily be fatal.
How can you prevent HIV infection?
The best ways to prevent HIV infection are to practice safe sex always and never share needles. There are also medications — called PrEP and PEP — that significantly reduce your risk of developing HIV, even if you have contact with the virus.
PrEP is short for pre-exposure prophylaxis and is recommended for consistent use by anyone in a high-risk group for encountering the virus. As long as you take it as instructed, it will likely destroy any virus before it can take hold.
PEP is short for post-exposure prophylaxis and is a type of medication you can take in emergencies: specifically as soon as possible within 72 hours after potential exposure. If taken correctly, it can prevent the virus from causing HIV.
How do you know if you have HIV?
The only way to know whether you have HIV or not is to get tested. You can purchase at-home tests in many pharmacies and online. At-home tests are sometimes given out for free from community health programs. Tests are also available at most medical facilities and are a straightforward procedure.
Be sure to talk to your doctor or another medical professional as soon as possible if you have any concerns about HIV or believe you were recently exposed.

SLIDESHOW
A Timeline of the HIV/AIDS Pandemic See SlideshowCenters for Disease Control and Protection: "About HIV," "AIDS and Opportunistic Infections," "HIV Treatment," "PEP (Post-Exposure Prophylaxis)," "PrEP (Pre-Exposure Prophylaxis)."
hiv.gov: "What is HIV?"
National Institute of Health HIV Info: "HIV and AIDS: The Basics," "The Stages of HIV Infection."
World Health Organization: "HIV Data and Statistics," "Interim WHO Clinical Staging for HIV/AIDS and HIV/AIDS Case Definitions for Surveillance."
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