HIV (Human Immunodeficiency Virus) is a virus that attacks the body’s immune system. If HIV is not treated, it can lead to AIDS (Acquired Immune Deficiency Syndrome). There is currently no effective cure. Once people get HIV, they have it for life. But with proper medical care, HIV can be controlled. People with HIV who get effective HIV treatment can live long, healthy lives and protect their partners.


HIV infection in humans came from a type of chimpanzee in Central Africa. The chimpanzee version of the virus (called Simian Immunodeficiency Virus or SIV) was probably passed to humans when humans hunted these chimpanzees for meat and came in contact with their infected blood. Studies show that HIV may have jumped from chimpanzees to humans as far back as the late 1800s. Over decades, HIV slowly spread across Africa and later into other parts of the world. We know that the virus has existed in the U.S. since at least the mid to late 1970s.


The only way to know for sure whether you have HIV is to get tested. Knowing your HIV status helps you make healthy decisions to prevent getting or transmitting HIV. Find an HIV testing site near you.


Some people have flu-like symptoms within 2-4 weeks after infection (called acute HIV infection). These symptoms may last for a few days or several weeks. Possible symptoms include:

    • Fever
    • Chills
    • Rash
    • Night sweats
    • Muscle aches
    • Sore throat
    • Fatigue
    • Swollen lymph nodes
    • Mouth ulcers

However, some people may not feel sick during acute HIV infection. These symptoms don’t mean you have HIV. Other illnesses, such as the flu, can cause these same symptoms.

See a healthcare provider if you have these symptoms and think you may have been exposed to HIV. Getting tested for HIV is the only way to know for sure.


When people with HIV don’t get treatment, they typically progress through three stages. HIV medicine can slow or prevent progression of the disease and with advancements in antiretroviral treatment (ART), progression to Stage 3 is less common today than in the early days of HIV.

Stage 1: Acute HIV Infection

    • People have a large amount of HIV in their blood. They are very contagious. The number of HIV particles in the blood is much higher during acute HIV infection than later on. Exposure to the blood of someone in the acute phase of infection is more likely to result in infection than exposure to someone with long-term infection.
    • Some people have flu-like symptoms. This is the body’s natural response to infection. But some people may not feel sick right away or at all.
    • If you have flu-like symptoms and think you may have been exposed to HIV, seek medical care and ask for a test to diagnose acute infection. Only antigen/antibody tests or nucleic acid tests (NATs) can diagnose acute infection.

Stage 2: Chronic HIV Infection

    • This stage is also called asymptomatic HIV infection or clinical latency.
    • HIV is still active but reproduces at very low levels.
    • People may not have any symptoms or get sick during this phase.
    • Without taking HIV antiretroviral medications (ARVs), this period may last a decade or longer, but some may progress faster.
    • People can transmit HIV in this phase.
    • At the end of this phase, the amount of HIV in the blood (viral load) goes up and the CD4 cell count goes down. The person may have symptoms as the virus levels increase in the body and the person moves into Stage 3.
    • People who take ARVs as prescribed may never move into Stage 3.

Stage 3: Acquired Immunodeficiency Syndrome (AIDS)

    • The most severe phase of HIV infection.
    • People with AIDS have such badly damaged immune systems that they get an increasing number of severe illnesses, called opportunistic infections (OIs).
    • People receive an AIDS diagnosis when their CD4 cell count drops below 200 cells/mm3 or if they develop certain OIs.
    • People with AIDS can have a high viral load and be very infectious.
    • Without treatment, people with AIDS typically survive about 3 years.

U.S. ART guidelines recommend treatment for all people with HIV. Starting ART during acute HIV infection might protect the HIV-specific immune response.


HIV (Human Immunodeficiency Virus) is a virus that attacks the body’s immune system. If HIV is not treated, it can lead to AIDS (Acquired Immunodeficiency Syndrome). Learning the basics about HIV can keep you healthy and prevent HIV transmission.

It’s not easy to identify people with acute HIV infection. Some people have no symptoms. If they have symptoms, several other diseases like the flu might be causing them.

If you think you might be in the acute stage of HIV infection, tell your healthcare provider and get tested. Talk to your healthcare provider about the advantages of starting ART during acute HIV infection.

Without ART, people will pass from the acute stage of HIV infection to the chronic stage and then on to AIDS.

Reviewed January 2021

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