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The Basics of HIV

Reviewed by: HU Medical Review Board | Last reviewed: March 2024 | Last updated: March 2024

Human immunodeficiency virus (HIV) is a virus that lives in the blood. The virus attacks the immune system, making it hard to fight off infections and diseases. The body cannot get rid of HIV, so if you have it, you have it for life.1

While HIV cannot be cured, it can be treated with a group of drugs called antiretroviral therapy (ART). With ART treatment, people with HIV can live long, productive lives. If HIV is not treated, it can lead to acquired immunodeficiency syndrome (AIDS).1

Where did HIV come from?

Doctors believe HIV jumped from chimpanzees to humans sometime in the late 1800s. The chimpanzee version of the virus is called simian immunodeficiency virus. They believe it moved from chimps to humans when humans ate the meat of an infected animal.2

Over the years, the virus spread from Africa to other parts of the world. It arrived in the United States in the 1970s.2

Who gets HIV?

Anyone can get HIV. Most people living with HIV got it through unprotected anal or vaginal sex, or by sharing drug equipment like needles, syringes, or cookers. HIV also can be passed from mother to child during breastfeeding.3

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The virus is transmitted from one person to another through certain body fluids, including:3

  • Blood
  • Semen or pre-seminal fluid (cum or pre-cum)
  • Rectal fluids
  • Vaginal fluids
  • Breast milk

These fluids must either enter the bloodstream directly or come in direct contact with a certain type of skin called a mucous membrane. Mucous membranes are found in the mouth, penis, vagina, and rectum.3

Babies also may be born with HIV if their mother has HIV and is not treated while she is pregnant.4

How common is HIV?

About 1.2 million people in the United States are living with HIV. Of those, nearly 9 out of 10 know they have HIV. About 36,000 new people get HIV each year. In the United States, HIV infection is more common in the south, the northeast, California, and Puerto Rico.5

Men who have sex with men account for 6 out of 10 new cases. People who have sex with the opposite sex account for 2 out of 10 new cases, and people who inject drugs make up the final 2 out of 10.5

Certain groups of people in the United States are more often impacted by HIV than others. For example, Black Americans, especially Black men who have sex with men, and Hispanic/Latino people are affected by HIV more often than other racial groups.5

How is HIV diagnosed?

The only way to know whether you have HIV is to get an HIV test. You can get this test at your doctor’s office, a health clinic, a substance abuse program, or a hospital. You also may be able to use a self-test.1

Testing is important because getting diagnosed and beginning treatment can protect your life and the lives of your sexual partners. People with HIV who take their drugs as prescribed can live long lives. And they have an extremely small chance of transmitting the virus to other people through sex or during pregnancy.1

What is the difference between HIV and AIDS?

HIV is the virus that causes AIDS. AIDS is the last and most serious stage of HIV. In the United States, most people never develop AIDS because so many are tested and then receive treatment.1

However, some people go untreated because they do not know they have HIV. Others may stop taking their HIV drugs. In either case, these people will eventually develop AIDS. A person is diagnosed with AIDS if:1,6

  • Their CD4 cells are below 200 cells per cubic millimeter of blood. CD4 cells are a key part of the immune system. They help fight infection and disease. Someone with a healthy immune system has between 500 and 1,600 cells/mm3.
  • They have one or more of the infections closely linked to AIDS. These infections include certain kinds of pneumonia and herpes, thrush (a fungal infection), tuberculosis, salmonella, and toxoplasmosis.

How is HIV treated?

People who receive HIV treatment, especially early in the infection, are likely to live a normal life. Treatment plans for HIV generally include:7,8

ART helps people keep their CD4 count high and reach undetectable levels of the virus. Once a person has reached an undetectable viral load in their blood, they likely cannot transmit the virus to others.1