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HIV and AIDS Center

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on March 16, 2020.

How Many People Have AIDS?

The U.S Centers for Disease Control (CDC) first recognized AIDS (Acquired Immunodeficiency Syndrome) in 1981.

  • Roughly 1.1 million people in the U.S. are diagnosed with HIV at the end of 2016, including roughly 14%, or 1 in 7, who do not know they are infected. These are the most recent data from CDC.1
  • In 2018, 37,832 people received an HIV diagnosis in the US and dependent areas
  • From 2010 to 2017, new HIV infections among adults and adolescents in the US declined by an estimated 11%.
  • Worldwide, over 20 million people were accessing antiretroviral therapy in 2018.
  • Gay, bisexual, and other men who have sex with men are most at risk, representing about 70% of these new HIV infections.1

Diagnostic testing and treatment has improved drastically in the decade since AIDS was identified, prolonging the extent and quality of life. However, high-risk behavior is still prevalent in some communities and continued testing, diagnosis, treatment and prevention remains a national health objective.

Related Reading: HIV Prevention: PrEP and Other Options

How do you get HIV?

HIV (human immunodeficiency virus) is transmitted through body fluids:

  • Sexual contact with an HIV-infected partner.
  • Infected blood transfusion - rare today due to thorough screening.
  • Shared needles and syringes contaminated with infected blood.
  • Accidental needle stick injury.
  • Mother to child transmission (via pregnancy or breastfeeding).
  • In rare cases the virus may be transmitted through organ or tissue transplants, through artificial insemination with donated semen, or through unsterilized dental or surgical equipment.

HIV is not transmitted via ordinary contact (hugging, dancing, sneezing, talking, touching, or shaking hands) with someone who has HIV or AIDS. HIV is also not transmitted through sweat, tears or saliva; or through sharing food, utensils, towels, bedding, a swimming pool, telephone or toilet seat with someone who has the virus. Plus, HIV is not transmitted through bedbugs or mosquitoes.

What does the HIV virus do?

  • When a foreign organism enters the body, it is attacked by white blood cells and antibodies in a response coordinated by CD4 lymphocytes (these are a type of white blood cell and are also known as T-cells). These white blood cells help you to recover from disease and infections.
  • When the body is infected with HIV, the HIV virus attaches to the CD4 lymphocytes and enters the cells. Once inside, the virus inserts its own genetic material into the CD4 lymphocytes and then replicates itself.
  • When the new copies of the virus break out of the host cells and enter the bloodstream, they search for other cells to attack. The cycle repeats itself again and again. In the process, more than 10 billion new HIV particles are produced every day.
  • To counter this huge virus production, the immune system turns out as many as two billion new CD4 cells daily.
  • Eventually, the virus wins. The number of CD4 cells progressively decreases and the body develops severe immune deficiency whereby it is no longer able to effectively fight off viruses and bacteria that cause disease.
  • AIDS is the final and most serious stage of HIV disease, in which the signs and symptoms of severe immune deficiency have developed.

What is the difference between HIV and AIDS?

HIV (Human Immunodeficiency Virus) damages or destroys the cells of the immune system, making the body less able to fight infection and more susceptible to life threatening opportunistic infections.

The term AIDS (Acquired Immunodeficiency Syndrome) refers to the latter stages of HIV infection. Most individuals infected with HIV will progress to AIDS if not treated; however, there are very small numbers of patients who develop AIDS very slowly or not at all.

Who Should Be Tested For HIV / AIDS?

According to the latest CDC guidelines, patients in all healthcare settings should be offered the option for HIV/AIDS testing:

  • HIV screening is recommended for all patients ages 13–64 years in all healthcare settings after the patient is notified that testing will be performed unless the patient declines (opt-out screening).2,3 CDC also recommends that individuals get tested at least once in their lifetimes. A repeat test is recommended if you have new risk factors. Some experts may recommend screening up to age 75.
  • Persons at high risk for HIV infection should be screened for HIV at least once per year; in some cases every 6 months. High-risk groups include:
    • those with multiple sex partners
    • men who have sex with other men
    • those who engage in unprotected sex
    • intravenous (IV) drug users
    • those who had sex with a known HIV-positive partner or someone whose HIV status you do not know (anal or vaginal)
    • those who had more than one sex partner since their last HIV test
    • if diagnosed with or treated for hepatitis or tuberculosis (TB) or a sexually transmitted disease
    • if you exchange sex for drugs or money
    • those who had sex with someone whose sexual history you don’t know.2,3,13
  • Sexually active gay and bisexual men may benefit from getting an HIV test more often, every 3 to 6 months.
  • Testing is also recommended before entering a new sexual relationship; if you are pregnant; or if you have symptoms of another sexually transmitted disease.
  • Screening should be voluntary for the patient and performed only when the patient understands that an HIV test is being administered.

According to guidelines for HIV/AIDS testing in pregnant women:

  • HIV screening should be included in the routine panel of prenatal screening tests for all pregnant women. With early treatment, the risk of transmitting HIV to the baby can be very low.
  • Repeat screening in the third trimester is recommended in certain jurisdictions with elevated rates of HIV infection among pregnant women.
  • HIV treatment guidelines strongly suggest a combination of medicines that act to prevent the transmission of HIV to an infant from an HIV-infected mother.4,13

The U.S. Preventive Services Task Force (USPSTF) recommends that clinicians screen adolescents and adults ages 15 to 65 years for HIV infection, as well as younger adolescents and older adults who are at increased risk. (Grade A) The USPSTF also recommends that clinicians screen for HIV infection in all pregnant persons, including those who present in labor or at delivery whose HIV status is unknown. (Grade A).5

There is a strong advantage to knowing one's HIV status and starting treatment early. Early treatment can result in a near-normal life-span in an HIV-positive patient. This highlights the importance of routine HIV testing to reach a larger population and foster better health outcomes.

Learn More: Every June 27th is National HIV Testing Day

How is HIV Diagnosed?

HIV is most commonly diagnosed by testing your blood or saliva for antibodies to the virus.

Antigen-Antibody Combination Tests

Antigen-antibody combination tests (fourth generation tests) detect the presence of antibody as well as the p24 protein (antigen) of HIV, a protein that is present immediately after viral infection.6,8

  • Fourth generation HIV-1/HIV-2 immunoassays are recommended for first-line use in the CDC guideline updates, and are the preferred test.9 The sensitivity and specificity of these tests approach 100% in chronic HIV infection A list of commonly used assays can be found on the FDA website.7
  • According to the January 2018 CDC algorithm, no further tests are required if a fourth generation test is negative. However, if there is a possibility of very early infection leading to a non-reactive initial antigen/antibody immunoassay, such as when recent HIV exposure is suspected or reported, then conduct an HIV-1 RNA test or request a new specimen and repeat the algorithm according to CDC guidance.8
  • If the test is positive, a further confirmatory HIV-1/HIV-2 antibody differentiation immunoassay is recommended. Selection of a test that also determines if the patient is infected with HIV-1, HIV-2, or both is suggested, as this can affect treatment choices.8

These tests can allow earlier diagnosis and treatment of HIV disease. Additionally, the fourth generation tests may play a role in preventing spread of infection due to earlier diagnosis and counseling on behavior modification.

It takes time for your body to develop these antibodies -- usually about 12 weeks. For negative or indeterminate HIV-1/HIV-2 immunoassays, a plasma HIV RNA level should be determined.

Nucleic acid test or NAT

A Nucleic Acid Test or NAT can be used in the early phase of HIV during the antibody negative time frame to detect HIV-1 RNA. An HIV RNA test checks for RNA genetic evidence from the virus in a sample of blood, not the antibodies. These tests may be useful for detecting suspected HIV-1 infection soon after exposure, about 7 to 28 days after exposure, but do not typically offer an advantage over antigen-antibody testing. 

RNA qualitative tests may also be used as an additional test to confirm HIV-1 infection in an individual who is positive for HIV-1 antibodies. This test can also be used to measure the level of virus RNA in the blood known as the “viral load.” Results may take a few days or more.9

ELISA Tests for HIV

HIV is diagnosed by testing the blood for the presence of antibodies, antigens or RNA to the virus. Antibodies are proteins produced in your body in response to other substances called antigens from the virus. In the past, this was often performed using a simple blood test known as an enzyme-linked immunosorbent assay (ELISA or EIA) screening test. These tests were, and still are in some cases, used for routine diagnostic screening. ELISA test was approved for HIV testing in the mid-1980s. Tools for HIV testing may depend upon the resources available at any one clinic.

HIV ELISA tests are not accurate immediately after infection because it may take up to 12 weeks for the body to develop antibodies to the virus. During this window of time, an infected person can transmit HIV to others because their infection is not detectable by a standard ELISA HIV-antibody screening test. In addition, patients may go undiagnosed because of a false-negative. ELISA tests results may take up to several days, or in some cases weeks.

When the ELISA screening test is positive (i.e. if there are HIV antibodies present in the blood) the test will be repeated. A positive ELISA test does not necessarily mean the person has HIV. Certain conditions can lead to false positive results, such as autoimmune diseases, liver diseases, multiple pregnancies, blood transfusions, or influenza. These conditions can stimulate the immune system to produce antibodies that cross-react with HIV antigens leading to a false positive.

Western Blot: No Longer Recommended

The CDC no longer recommends using the Western blot technique to confirm the presence of HIV-1 antibodies.10,11 In the past, if the second ELISA test was also positive for HIV antibodies, another blood test, called a Western blot test, could confirm the result through the detection of antibodies specific for HIV proteins. The FDA approved the Western Blot Test in 1987. However, this test is not recommended anymore for HIV testing due the preference for antigen-antibody tests.

Rapid HIV Antibody Tests

Rapid HIV antibody tests allow testing at a clinic or at-home with a result within 20 minutes. These screening tests are best used in conjunction with a history, clinical exam by your doctor, and risk assessment.

If a rapid test is positive a follow-up test with your doctor MUST be performed. Like the ELISA, these tests may give a false negative in the early window of the first 3 to 12 weeks after initial HIV infection because detectable levels of antibody have not formed.

Examples of antibody rapid tests used in clinics (not home) that test blood, plasma or oral fluid for diagnosis include:

HIV Home Test Kits

The FDA approved the OraQuick In-Home HIV Test in 2012. The OraQuick In-Home HIV Test does not require sending a sample to a laboratory for analysis. The kit, which tests a sample of fluid from your mouth, is approved for sale in stores and online to anyone age 17 and older. The Home Access HIV-1 test, which required a finger stick for a blood sample at home, is no longer marketed.12

The test checks for antibodies to HIV-1 and HIV-2. Positive test results using the OraQuick test must be confirmed by follow-up laboratory-based testing by seeing your doctor. Also, the test can be falsely negative if HIV infection occurs within three months before testing.

Once a person is diagnosed with HIV, a further blood test (a viral load test, which measures the amount of virus in the blood) will help determine the probable progression of the disease. Viral load tests are also used to manage the drug treatments that will be administered following diagnosis.

If you buy your home test online or from any retailer make sure the HIV test is FDA-approved.12

See Also

Learn more

Treatment options

Care guides

Symptoms and treatments guides (external)


  1. Centers for Disease Control and Prevention. HIV/AIDS. Basic Statistics. (CDC). Accessed March 14, 2020 at
  2. Centers for Disease Control and Prevention (CDC). HIV Testing. Accessed May 31, 2018 at
  3. Centers for Disease Control and Prevention (CDC). Testing. Accessed March 15, 2020 at
  4. Centers for Disease Control and Prevention (CDC). An Opt-Out Approach to HIV Screening. Accessed March 15, 2020 at
  5. U.S. Preventive Services Task Force. (USPSTF). Human Immunodeficiency Virus (HIV) Infection: Screening. Updated June 2019. Accessed March 15, 2020 at
  6. Sax P, et al. Screening and diagnostic testing for HIV infection. Up to Date. June 2019. Accessed March 15, 2020 at
  7. Complete List of Donor Screening Assays for Infectious Agents and HIV Diagnostic Assays. US Food and Drug Administration (FDA). Updated: 04/03/2018. Accessed May 31, 2018 at
  8. Centers for Disease Control and Prevention (CDC). 2018 Quick reference guide: Recommended laboratory HIV testing algorithm for serum or plasma specimens
  9. Patient education: Testing for HIV (Beyond the Basics). Up to Date. Accessed March 16, 2020 at
  10. HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes. Quest Diagnostics. Accessed March 15, 2020 at
  11. Limitations for the Use of HIV-1 Western Blot in Plasma/Serum. American Society of Microbiology. Association of Public Health Laboratories. June 2015. Accessed March 15, 2020 at
  12. US Food and Drug Administration (FDA). Vaccines, Blood & Biologics. Testing for HIV. Updated: 09/18/2019. Accessed March 16, 2020 at
  13. Centers for Disease Control and Prevention (CDC). HIV/AIDS. Guidelines and Recommendations. Accessed March 16, 2020 at

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.