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Medically reviewed on Aug 27, 2013 by L. Anderson, PharmD

AIDS is a global epidemic. The U.S Centers for Disease Control (CDC) first recognized AIDS in 1981. Roughly 56,000 new cases of HIV infection are diagnosed each year in the U.S. In 2012, more than one million people in the U.S. are living with HIV, the virus that causes AIDS, but 20 percent do not know that they are infected.

Diagnostic testing and treatment has improved drastically over the last 30 years, prolonging the extent and quality of life. However, high-risk behavior is still prevalent in some communities and continued testing, diagnosis and treatment remains a national health objective.

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 the latest CDC guidelines, patients in all healthcare settings should be offered the option for HIV/AIDS testing1:

  • HIV screening is recommended for patients in all healthcare settings after the patient is notified that testing will be performed unless the patient declines (opt-out screening).
  • Persons at high risk for HIV infection should be screened for HIV at least annually.
  • Separate written consent for HIV testing should not be required; general consent for medical care should be considered sufficient to encompass consent for HIV testing.
  • Prevention counseling should not be required with HIV diagnostic testing or as part of HIV screening programs in healthcare settings.

According the CDC 2006 guidelines for HIV/AIDS testing in pregnant women1:

  • HIV screening should be included in the routine panel of prenatal screening tests for all pregnant women.
  • HIV screening is recommended after the patient is notified that testing will be performed unless the patient declines (opt-out screening).
  • Separate written consent for HIV testing should not be required; general consent for medical care should be considered sufficient to encompass consent for HIV testing.
  • Repeat screening in the third trimester is recommended in certain jurisdictions with elevated rates of HIV infection among pregnant women.

How is HIV Diagnosed?

HIV is diagnosed by testing the blood for the presence of antibodies, antigens or RNA to the virus. Most often, this is performed using a simple blood test known as an enzyme-linked immunosorbent assay (ELISA or EIA) screening test. These tests are used for routine diagnostic screening. ELISA test was approved for HIV testing in the mid-1980s.

Unfortunately, HIV ELISA tests are not accurate immediately after infection because it may take 3 to 12 weeks for the body to develop antibodies. 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.

However, if 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 Lyme disease or lupus erythematosus.

However, if the second test is also positive for HIV antibodies, another blood test, called a Western blot test, will confirm the result through the detection of antibodies specific for HIV proteins. The FDA approved the Western Blot Test in 1987.

The Western Blot test is important as a follow-up confirmatory test because non-HIV antibodies can cause a false positive result on the ELISA test. Combining the two types of tests helps ensure that the results are accurate. If all three tests are positive a diagnosis of HIV infection will be given.

Although ELISA and Western Blot are the standard screening tests for HIV, other tests are available that can diagnosis acute HIV during the early window period when antibodies are not detectable. An HIV qualitative RNA test (for example APTIMA) can be used in the acute phase of HIV during the antibody negative time frame to detect HIV-1 RNA. HIV-1 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.

Fourth generation antigen-antibody combination tests (for example, Abbott Architect HIV Ag/Ab Combo Assay) were approved in 2010 and detect the presence of antibody as well as the p24 protein (antigen) of HIV, a protein that is present immediately after viral infection. This test, which reduces the window period for HIV detection by rough 5 days, can allow earlier diagnosis and treatment of HIV disease. Additionally, the 4th generation tests may play a role in preventing spread of infection due to earlier diagnosis and counseling on behavior modification. Health experts also suggest these tests can be more efficient and cost-effective because they prevent the need for multiple screening and confirmatory tests.

Rapid HIV antibody tests became available from 2002 to 2006 and allow point-of-care testing or at-home diagnosis. These screening tests are best used in conjunction with a history, clinical exam, and risk assessment. If a rapid test is positive a follow-up Western Blot should be performed. Like the ELISA, these tests may give a false negative in the early window of the first 3-12 weeks after initial HIV infection because detectable levels of antibody have not formed.

Examples of antibody rapid tests used in clinics that test blood, plasma or oral fluid for diagnosis include:

  • OraQuick
  • Uni-Gold
  • Clearview Complete HIV ½
  • Clearview HIV 1/2 Stat Pak

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 test checks for antibodies to HIV. Positive test results using the OraQuick test must be confirmed by follow-up laboratory-based testing. Also, the test can be falsely negative for reasons that include the occurrence of HIV infection within three months before testing.

Prior to approval of the OraQuick, the only HIV home testing kit approved by FDA and legally sold in the U.S. was the Home Access HIV-1 Test System manufactured by Home Access Health. This test requires that blood samples be taken at home and then sent to a laboratory for testing. Anonymous results and counseling are provided over the phone.

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.

How is AIDS diagnosed?

AIDS is diagnosed when a person is HIV positive and either has a CD4 lymphocyte (T-cell) count of less than 200 or develops one of the AIDS-defining diseases.

For further information see HIV and AIDS: Symptoms and Complications

How does the HIV virus affect the immune system?

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). 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 2 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.

How is HIV transmitted?

HIV is transmitted through body fluids:

  • Sexual contact with an HIV-infected partner
  • Infected blood - rare nowadays due to thorough screening
  • Shared needles and syringes contaminated with infected blood
  • Accidental needle stick injury
  • Mother to child transmission (via pregnancy or breast-feeding)
  • In rare cases the virus may be transmitted through organ or tissue transplants, through artificial insemination with donated semen, or through un-sterilized 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 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. HIV is not transmitted through bedbugs or mosquitoes.

See Also:

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  1. 1. Centers for Disease Control and Prevention. Revised recommendations for HIV testing of adults, adolescents, and pregnant women in health-care settings. MMWR Recommendations and Reports. September 22, 2006/55(RR14);1-17. Accessed June 26, 2012.