What are HIV and AIDS?

Acquired immune deficiency syndrome, better known as AIDS, is caused by infection with the human immunodeficiency virus (HIV). AIDS is the most advanced stage of HIV infection.

Over time, the virus attacks and destroys the body’s immune system (the system that protects the body from disease). Without a fully working immune system, a person is at risk for getting other infections that usually don’t affect healthy people. These are called opportunistic infections. People with HIV also have a greater risk of getting certain types of cancer, such as Kaposi sarcoma, lymphoma, and cervical cancer, as well as other health problems. Many of these problems can threaten life.

More than 1 million people in the United States are now living with HIV infection, and nearly 500,000 are living with AIDS. Women account for about 1 out of 4 people infected with HIV in this country. Each year, about 50,000 people become newly infected with HIV in the United States.

Worldwide, about 35 million people are living with HIV/AIDS. More than half of these people live in sub-Saharan Africa. About half are women.

Spread of HIV infection

HIV can spread from one person to another when blood or certain body fluids (semen, vaginal secretions, or breast milk) from an infected person get into an uninfected person. Routes of spread include:

  • Unprotected vaginal, anal, or oral sex with an infected person
  • Sharing needles or drug equipment with injection drug users who have HIV
  • Prenatal (before birth) and perinatal (during and right after birth) exposure of infants whose mothers are infected with HIV
  • Breastfeeding by mothers with HIV
  • Transfusion of blood products containing the virus
  • Organ transplants from HIV-infected donors
  • Penetrating injuries or accidents of health care workers (usually needle sticks) while caring for HIV-infected patients or handling their blood

HIV is not spread by mosquitoes, ticks, or other insects. It can’t be spread by casual contact such as talking, shaking hands, hugging, sneezing, sharing dishes, sharing bathrooms, sharing telephones or computers, or through water. It is not spread through saliva, tears, or sweat.

Transfusions of blood and blood products caused some of the HIV infections in the early 1980s. With new precautions and careful testing at blood banks, this risk has been almost eliminated.

Preventing HIV infection and AIDS

Because of how HIV is spread, there are ways to avoid HIV infection and prevent AIDS.

Most HIV infections throughout the world are passed to other people through sex. This means that not having unprotected sex with infected persons can prevent most HIV infections. If both partners are uninfected, and both carefully avoid activities that might result in getting HIV (both partners have sex only with each other and do not share needles with others), unprotected sex can be safe. If you do have sexual contact with a partner whose HIV status is uncertain, using latex or plastic condoms every time, from start to finish, can greatly lower your risk.

The second most common cause of HIV infection is sharing used needles or drug equipment with injection drug users who have HIV. For people who inject drugs, the safest way to avoid HIV is to quit. However, some people are unable to quit on their own or get help in quitting, and they may not be able to stop using drugs right away. For these people, using clean, sterile needles and injection supplies can help protect them. In some areas, there are programs to make sure that drug users can get sterile needles and syringes. Nearly everywhere these programs have been started, they have reduced the number of new HIV infections in users who inject drugs.

For people who are at high risk of HIV infection, such as injection drug users and people whose partners have HIV, taking medicine (as a pill every day) is another way to help lower your risk of infection. This is known as pre-exposure prophylaxis, or PrEP. People who use PrEP need to be willing to take the pill every day and to see their health care provider every few months for repeat HIV tests, prescription refills, and follow-up.

In case of a single possible exposure to HIV, such as from a broken condom or another type of exposure from a person who might have HIV, one option might be “morning-after” treatment to try to reduce the risk of infection. This treatment consists of taking anti-HIV drugs every day for 4 weeks. They are likely to work best if they are started within 24 hours of the exposure and are rarely started more than 72 hours afterward.

HIV-infected mothers can pass the virus to their babies during pregnancy, delivery, or breastfeeding. Treating the mothers and infants with anti-HIV drugs, delivering the baby by C-section, and avoiding breastfeeding can greatly reduce the risk of these infections.

Organ and tissue transplants from human donors carry a very small risk of HIV and other infections. But donors are carefully screened and tested to reduce the risk as much as possible.

How is HIV infection diagnosed?

Because HIV infection often has no symptoms for years, a person can have HIV for a long time and not know it. People often believe that if they have had a physical exam, the doctor has checked for HIV. This is often not true. Although the US Centers for Disease Control and Prevention (CDC) recommends that everyone between the ages of 13 and 64 be tested for HIV at least once, HIV testing is often not done unless you have certain medical problems, are pregnant, or ask to be tested.

Most of the time, a person who is tested will know it, although there are a few cases where people may not be told they are getting an HIV test, such as people entering military service and some people who apply for individual health or life insurance policies.

If you have any doubt about your HIV status, talk with your doctor or visit a health department clinic where testing is offered. To have the HIV test done without giving your name and address (anonymous testing), you can buy a home collection kit at the drugstore or online, or go to a special anonymous testing site. Some state health departments also offer anonymous HIV tests.

People who do not seek HIV testing might not learn that they have HIV until they develop early symptoms or even AIDS. But with testing, HIV infection can be detected and treatment started before a person gets seriously ill.

Tests to detect HIV infection

HIV is most often found using screening tests that look for anti-HIV antibodies (immune system proteins) in the blood. Other tests look for antibodies in fluid in the mouth. When the body is infected with HIV, it starts to make antibodies against the virus to try to fight it. Although these antibodies can't get rid of HIV, they can usually be found in the blood and some other body fluids within several weeks after infection. HIV screening tests look for these antibodies, not the virus itself. The virus is harder to detect than the antibodies.

You can get tested for HIV in many settings (doctors’ offices, hospitals, neighborhood clinics, and health department clinics). And there are HIV test kits you can buy at the drugstore that let you collect samples at home. You then either test the sample yourself or send it off to a lab to be tested.

Tests in doctors’ offices and clinics

In doctors’ offices and clinics, testing is often done on a blood sample collected from a vein or a finger stick, although mouth fluids may be tested as well.

Some types of samples are sent off to a lab for testing, and results are available in as little as a few days up to a couple of weeks. Testing locations usually prefer that you return in person for your test results.

Some doctors’ offices and clinics offer quick HIV tests. These screening tests use blood or oral fluid and offer preliminary results within half an hour.

Testing at home

There are 2 types of at-home tests as well. For one type of test kit, you swab the inside of your mouth to get a fluid sample and test it by placing it in a special tube. This test can give you results in about half an hour. For the other type of test, you collect a small sample of blood from your finger and mail it off to a lab for testing. You can then get the results by phone within a few days.

You can buy home test kits from most drugstores or similar stores. While you can buy legitimate home test kits from some online retailers, other tests being sold online may not be reliable, so be sure to get one from a place you trust.

Test results

If the first result with any type of screening test is positive (that is, if it finds something that may be anti-HIV antibodies), it does not always mean that you are infected with HIV. Other tests of blood samples will need to be done to confirm the infection. If you are using an at-home test kit, you should see a doctor, who will do more tests to be sure of the diagnosis.

If the first test result is negative (that is, if it does not find anti-HIV antibodies), in most cases no further testing is needed. But it’s important to know that a negative test result does not mean for sure that a person does not have HIV. It often takes several weeks after becoming infected with HIV (and sometimes longer) before enough antibodies are in the blood or other body fluids to be detected. Tests done before this may be negative, even if a person is infected. To be sure that the person doesn’t have HIV, the person should be tested at least 3 months after the most recent suspected exposure.

How is AIDS defined?

A person can have HIV infection and not have AIDS. AIDS happens when the HIV infection has badly damaged the immune system, a process that may take years. In the United States and other developed countries, the average time from getting infected with HIV to advanced AIDS is about 10 years if the person gets no treatment, but in some people this can happen faster.

HIV damages the immune system by infecting and killing a type of white blood cell known as a CD4 cell (or helper T-cell). In the later stages of HIV infection, the loss of these cells leads to a weakened immune system, which allows opportunistic infections (infections that the healthy body would usually fight off), some types of cancer, and other disorders to occur.

  • The CDC defines AIDS as having a positive HIV blood test, along with either: A blood CD4 count of less than 200 cells per cubic millimeter of blood (200/mm3). A normal CD4 count is about 500/mm3 to 1,600/mm3.
  • A major opportunistic condition, which includes certain infections, cancers, and syndromes that are often linked to AIDS, regardless of the CD4 count.

How are HIV infections and AIDS treated?

The treatment of HIV infection and AIDS is complex, and sudden illnesses can cause serious and even life-threatening problems. Because of this, it is very important to be treated by a doctor or clinician who has experience in treating people with HIV and AIDS.

Treatment for HIV/AIDS has 3 main goals:

  • Restore and preserve immune function
  • Keep the amount of HIV in the body as low as possible for as long as possible
  • Prevent, cure, or control opportunistic infections

All of these can help support a person’s quality of life by improving health and lowering the chance of serious illnesses and their long-term effects. Effective treatment also prolongs life.

The main treatment for HIV at this time uses 3 or more anti-HIV drugs taken each day to help block the virus from reproducing (making more viruses). Treating HIV with drugs is often called anti-retroviral therapy (ART) because HIV is a type of retrovirus. Combinations of anti-HIV drugs that are very good at stopping HIV growth are sometimes called highly active anti-retroviral therapy (HAART).

There are dozens of anti-HIV drugs that can be used in different combinations. The best combination varies with the person, disease stage, whether the person’s infection is resistant to any of the drugs, and other factors. Different combinations might need to be tried, and over time the drugs may need to be changed. Each drug carries some risks for certain side effects, which need to be discussed before starting. As part of caring for patients on anti-HIV drugs, doctors see the patients and check labs often.

By slowing viral growth and keeping the immune system as healthy as possible, treatment helps reduce the risk of some types of infections, AIDS-related cancers, and other health problems. With effective treatment, the disease progresses more slowly and people live longer. Still, no combination of drugs can actually cure the infection, so it’s important that people being treated keep taking their medicines. Sometimes 2 or even 3 HIV drugs are put together into just one or two pills to make the drug treatment easier to remember and take. Whether the medicines are taken together or separately, close follow-up and testing are needed to make sure the treatment is still working.

People infected with HIV may not need to start treatment right away. The best time to start is not always clear, because HIV infection usually progresses slowly, and anti-HIV drugs can have some fairly serious side effects over time. But doctors have found that outcomes are usually better if the anti-HIV drugs are started before the immune system has been seriously damaged. Most doctors agree that anti-HIV treatment should begin when the infection is causing serious symptoms or a person’s CD4 count falls below a certain level. There may be other reasons for thinking about starting treatment as well.

Other measures that can be taken to support the immune system involve good self-care, such as:

  • Eating well and getting regular exercise
  • Managing stress
  • Avoiding infections (which may include staying away from people who are sick, practicing food safety, getting certain vaccines, taking antibiotics, using safer sex practices, and other measures)
  • Stopping tobacco or other drug use

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Revised: July 25, 2014

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