Also Known As
Human Immunodeficiency Virus Infection
Acquired Immunodeficiency Syndrome
This article was last reviewed on
This article waslast modified on October 13, 2020.
What are HIV and AIDS?

HIV (human immunodeficiency virus) is the virus that causes AIDS (acquired immunodeficiency syndrome). If untreated, HIV can progressively destroy the body's ability to fight infections and certain cancers. It can weaken the immune system by infecting lymphocytes, a type of white blood cell, that normally help the body fight infections. Specific lymphocytes known as T-helper cells or CD4 cells are major targets for HIV. The virus binds to CD4 cells, enters them, replicates inside them, and eventually kills them.

Over time and without treatment, the amount of HIV virus—the viral load—can increase while the number of CD4 cells in the blood declines. After several years without treatment, the number of CD4 cells can drop to the point that AIDS-associated conditions and symptoms begin to appear. AIDS treatments can slow and even precent the disease from progressing by reducing the amount of HIV in the body. This allows the body's CD4 cells to increase or stabilize.

The Centers for Disease Control and Prevention (CDC) estimates that about 38,000 people in the U.S were diagnosed with HIV in 2018, the year with the most current statistics. Additionally, 1.2 million people in the U.S. are living with HIV infection, and nearly 14% of those with the infection are not aware of it and can pass the virus on to others. In 2018, nearly 16,000 people diagnosed with HIV died. These deaths may be due to any cause.

Worldwide, 690,000 died of AIDS-related illnesses in 2019 and 38 million people were living with HIV, according to the World Health Organization.

HIV can be spread the following ways:

  • By having unprotected sex with an infected partner; the virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex. Having a sexually transmitted disease (STD) such as syphilis, genital herpes, chlamydia, gonorrhea, or bacterial vaginosis appears to make people more susceptible to and at higher risk for acquiring HIV infection during sex with infected partners.
  • By sharing needles or syringes (such as with intravenous injection drug abuse), which can be contaminated with very small quantities of blood from someone infected with the virus.
  • HIV can be passed from mothers to their babies during pregnancy or childbirth. HIV also can be spread to babies through the breast milk of mothers infected with the virus. If the mother is treated with antiretroviral therapy (ART) during pregnancy, she can significantly reduce the chances of passing the infection to her baby.
  • Through contact with infected blood; in the U.S. today, because of screening blood for transfusion and heat-treating techniques and other treatments of blood derivatives, the risk of getting HIV from transfusions is extremely small. However, before donated blood was screened for evidence of HIV infection and before treatments were introduced to destroy HIV in some blood products, such as factor VIII and albumin, HIV was transmitted through transfusion of contaminated blood or blood components. In areas of the world where donated blood is not routinely screened or treated for HIV, there is still risk of contracting the disease through this mode of transmission.

Initially, HIV usually causes flu-like symptoms, but some people may not experience any obvious signs or symptoms. The only way to determine whether you are infected is through HIV testing.

Your HIV status, like other medical conditions and test results, is protected by the Health Insurance Portability and Accountability Act (HIPAA) Privacy Rule and cannot be shared by healthcare providers with friends, family, or employers without written permission. However, if you test positive for HIV, it is important that you tell your healthcare providers as well as all sex partners and/or anyone with whom you share needles. Counseling services are often available from the clinic or healthcare provider that performed the test and they can help to advise you on who needs to know.

HIV status may be shared with healthcare providers who have a "need to know" in order to treat you. Also, in order to determine the incidence of HIV and to provide appropriate prevention and care services, all new cases of HIV are reported to state and local health departments.

Development of AIDS

  • HIV may initially cause no symptoms or cause an acute illness with non-specific, flu-like symptoms that resolve after a week or two.
  • During the first few weeks following infection with HIV, the virus infects T-cells, making numerous copies of itself and continuing to infect more T-cells. The virus is present in large numbers and is carried throughout the body.
  • About 2 to 8 weeks after exposure, the immune system responds by producing antibodies against the virus.
  • As HIV infects CD4 T-cells, it slowly begins to decrease their numbers.
  • You may be apparently healthy for a decade or more, but without treatment, HIV continues to replicate and destroy CD4 T-cells that normally help the body fight infections. The virus remains in places such as the brain and lymph nodes, where it will persist even during drug treatment.

If you become infected with HIV and it is not detected early and treated, it may become a simmering infection that may cause few symptoms for a decade or more. If your infection is still not treated, eventually symptoms of AIDS emerge and begin to progressively worsen. Over time and without treatment, HIV destroys the immune system and your body’s ability to fight infections and certain cancers, leaving your body vulnerable to other debilitating diseases.

The term AIDS applies to the most advanced stages of HIV infection. According to the CDC, AIDS is diagnosed when the CD4 T-cell count drops below 200 cells/mm3. AIDS is also diagnosed when you have HIV and an AIDS-related illness, such as tuberculosis or pneumonia caused by Pneumocystis jirovecii (formerly called Pneumocystis carinii) a type of bacteria. In people with AIDS, opportunistic infections are often severe and sometimes fatal because the immune system is so damaged by HIV that the body cannot fight off certain bacteria, viruses, fungi, or parasites. Those with HIV/AIDS are also at an increased risk of developing certain cancers, neurological disorders, and a variety of other conditions.

Accordion Title
About HIV Infection and AIDS
  • Signs and Symptoms

    HIV initially may cause no noticeable symptoms or may cause an acute illness with non-specific, flu-like symptoms such as:

    • Fever 
    • Fatigue 
    • Headache 
    • Sore throat 
    • Rash 
    • Enlarged lymph nodes 

    In most people, the initial symptoms go away after a few weeks. The only way to be sure to know if you are infected is through HIV testing.

    If HIV is not diagnosed early and treated, it infects and kills more CD4 T-cells, decreasing their numbers. Your immune system may eventually become weakened to the extent that you begin having signs and symptoms such as:

    • Persistently enlarged lymph nodes
    • Recurring fever
    • Rapid weight loss
    • Profuse sweating, night sweats
    • Extreme fatigue
    • Persistent diarrhea
    • Rashes
    • Sores in the mouth or on the genitals or anus
    • Memory loss or difficulty concentrating

    In children who are infected with HIV at or before birth, symptoms may emerge within a couple of years. Untreated children may have delayed development and be frequently ill. Pneumonia is common in children born with HIV.

    If still left untreated, HIV can progress to AIDS, the most advanced stages of HIV infection. People diagnosed with AIDS may get life-threatening diseases called opportunistic infections caused by viruses, bacteria, fungi, or parasites. These infections do not usually make healthy people sick.

    Opportunistic infections common in people with AIDS cause signs and symptoms such as:

    • Coughing and shortness of breath
    • Sores on the mouth, anus or genitals
    • Red, pink, brown or purple blotches on or under the skin
    • Soaking night sweats
    • Shaking chills or a high fever for several weeks
    • Seizures and lack of coordination
    • Difficult or painful swallowing
    • Mental symptoms such as confusion and forgetfulness
    • Severe and persistent diarrhea
    • Vision loss
    • Nausea, abdominal cramps, and vomiting
    • Weight loss
    • Extreme fatigue
    • Severe headaches
    • Coma
  • Tests

    Laboratory tests
    The goals of HIV testing are to:

    • Screen for and diagnose HIV infection
    • Measure and monitor the amount of virus in your blood (the viral load)
    • Evaluate HIV's resistance to available treatments

    Screening
    HIV testing is the only way for you to know if you have an HIV infection. Early detection and treatment of HIV infection and immune system monitoring can greatly improve long-term health. Also, if you know your HIV status, it may help change behaviors that can put you and others at risk.

    Several organizations recommend routine screening for HIV. The Centers for Disease Control and Prevention (CDC), American College of Physicians (ACP), and the U.S. Preventive Services Task Force (USPSTF) recommend that anyone between the ages of 13 and 64 (or 15 to 65 in the case of the USPSTF) and pregnant women be screened for HIV at least once.

    Certain individuals should get tested at least once to learn their status, even if they are not between the ages of 13 and 64. These include:

    • People diagnosed with hepatitis, tuberculosis (TB) or a sexually transmitted disease
    • People who received a blood transfusion between 1978 and 1985 or had a sexual partner who received a transfusion and later tested positive for HIV
    • A healthcare worker with direct exposure to blood on the job
    • Any individual who thinks they may have been exposed

    Screening at least annually is advised for those at high risk for HIV and is recommended when you:

    • Have had unprotected sex with more than one partner since your last HIV test
    • Are a man who has had sex with another man (CDC says your healthcare practitioner may suggest that you get screened more often, such as every 3 to 6 months)
    • Have used street drugs by injection, especially when sharing needles and/or other equipment
    • Have exchanged sex for drugs or money
    • Have an HIV-positive sex partner
    • Have had sex with anyone who falls into one of the categories listed above or are uncertain about your sexual partner's risk behaviors

    For additional details on screening recommendations, see the articles for Teens, Young Adults, Adults, and Adults 50 and Up as well as Pregnancy and Newborns.

    Different types of tests may be used for HIV screening:

    • Combination HIV antibody and antigen test—this is the recommended screening test for HIV. It is available only as a blood test. It detects the HIV antigen called p24 plus antibodies to HIV-1 and HIV-2. (HIV-1 is the most common type found in the United States, while HIV-2 has a higher prevalence in parts of Africa.) The level of p24 antigen and the amount of virus (viral load) increase significantly soon after initial infection. Testing for p24 allows for detection of early infections, before HIV antibody is produced. About 2-8 weeks after exposure, antibodies to HIV are produced in response to the infection and remain detectable in the blood thereafter, making the antibody test useful for detecting infections weeks after exposure. By detecting both antibody and antigen, the combination test increases the likelihood that an infection is detected soon after exposure.
    • HIV antibody testing—all HIV antibody tests used in the U.S. detect HIV-1 and some tests have been developed that can also detect HIV-2. These tests are available as blood tests or tests of oral fluid.

    There are a few different ways you can get access to HIV screening:

    • A blood sample can be collected in a healthcare practitioner's office or a local clinic and sent to a laboratory for testing. Certain testing centers provide either anonymous (the name is never given) or confidential (the name is given but kept private) HIV testing and counseling. You can also contact your state or local health department to find out where testing may be available. To find a testing site near you, visit the CDC's GetTested resource.
    • In these same settings, there may be a rapid test available in which results are generated in about 20 minutes.
    • There is a home test for HIV test that uses a saliva sample and results are available in about 20 minutes. This allows you to remain anonymous and to get confidential results. The home test has two limitations:
      1. Saliva testing is less sensitive than a blood test, so the home test may miss some cases of HIV that a blood test would detect; and
      2. The home test is not as accurate when it is performed at home by a lay person compared to when it is performed by a trained healthcare professional. However, the convenience of home testing might encourage some people who might otherwise be reluctant to go to a healthcare practitioner or clinic to learn their HIV status.

    Diagnosis

    If any of the above screening tests is positive, then it must be followed by a second test to establish a diagnosis. This second test is an antibody test that is different than the first test. If the second test does not agree with the first test, then a third test is performed that detects the genetic material (RNA) of the virus.

    The CDC recommends the following testing protocol to screen for and diagnose HIV infection:

    • Screen for HIV infection using a combination HIV antigen/antibody test, then
    • Verify a positive with a second HIV antibody test that differentiates between HIV-1 and HIV-2.
    • If results of the first and second test do not agree, then the next test to perform is an HIV-1 RNA test (nucleic acid amplification test, NAAT). If the HIV-1 RNA is detected (positive), then the test to diagnose HIV is considered positive.

     

    HIV Testing Algorithm
    HIV Screening Algorithm. Courtesy of James Faix, MD


    Other tests:

    • HIV viral load testing—measures the amount of HIV in the blood; it is performed when you are first diagnosed to help determine the status of the disease and is ordered at intervals to monitor the effectiveness of therapy.
    • CD4 count—measures the number of CD4 T-cells in the blood; it is ordered when you are first diagnosed to get a baseline assessment of the immune system and done at intervals to monitor therapy and the status of the immune system. If you are doing well on treatment, this test may be done every 6 to 12 months.
    • HIV antiretroviral drug resistance testing, genotypic—ordered when you are initially diagnosed to determine whether the particular strain(s) of HIV that you have is resistant to certain antiretroviral drug therapies; also ordered when treatment is changed or when there is evidence of treatment failure.
    • Phenotypic resistance testing—sometimes ordered if you are resistant to multiple antiretroviral drugs to help guide treatment; this test evaluates whether your strain(s) of HIV can be inhibited by various concentrations of antiretroviral drugs.
    • Individuals who are planning to take the drug abacavir may be tested first for the gene allele, HLA-B*5701. If you are positive for it, you are at an increased risk of having a potentially severe hypersensitivity reaction and another drug should be considered. (Read more in the article on Pharmacogenetic Tests.)

    A number of other routine laboratory tests may be performed as part of your overall care. Several tests may be done to identify and monitor the treatment of opportunistic infections, complications, and drug toxicities. Testing may also be ordered at intervals to evaluate your overall health and organ function. Some examples include:

    Non-laboratory tests
    Testing such as a chest X-ray or an imaging scan may sometimes be performed to help evaluate the person's health status.

  • Prevention

    There is currently no cure for HIV infection and no vaccine to protect against it, but avoiding high-risk activities such as having unprotected sex and sharing needles for injecting drugs can help to prevent its spread. Routine screening for HIV helps identify HIV infections in people who may have no signs or symptoms. The early diagnosis of HIV infection is important to prevent its transmission to others.

    Treatment of HIV-infected mothers during pregnancy, precautions at birth, and avoiding breast-feeding can minimize the risk of passing the infection from mother to child. If you are already taking HIV medications when you become pregnant, you should continue to do so during pregnancy and labor and delivery. If you are not taking HIV medications or have a high viral load during pregnancy, getting the antiretroviral drug zidovudine intravenously during labor and delivery and treating the newborn twice a day by mouth for 6 weeks significantly reduces the rate of transmission from 25-33% to about 1-2%.

    Healthcare workers can protect themselves from HIV infection by following universal precautions, such as wearing gloves and avoiding needle sticks.

    Pre-exposure prophylaxis (PrEP)

    While there is no vaccine that prevents HIV, the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) recommend that individuals without HIV infection but at high risk for it consider taking pre-exposure prophylaxis (PrEP), a daily pill to help prevent infection. According to the CDC, PrEP reduces the risk of HIV from sex by about 99% for people who take it consistently. For those who inject drugs, PrEP reduces the risk of HIV by at least 74%.

    Post-exposure prophylaxis (PEP)

    Post-exposure prophylaxis (PEP) is another strategy for preventing HIV. PEP is taking antiretroviral medication after recent possible exposure to the virus. PEP should only be used in emergency situations and must be taken within 72 hours of possible HIV exposure. Talk to your healthcare practitioner or emergency department doctor about PEP right away if you:

    • Think you have may been exposed through sex (e.g., broken condom)
    • Think you were exposed through sharing needles or other works for injecting drugs
    • Were sexually assaulted
    • Are a healthcare worker and think you were exposed to HIV at work
  • Treatment

    The goals of HIV and AIDS treatment are to suppress the virus to undetectable levels and to preserve your immune system function and health. Suppressing viral replication prevents or inhibits HIV mutation and the development of drug resistance. It slows the progression of the disease and allows the number of CD4 T-cells to increase, improving immune function. Treatment of complications and opportunistic infections is also important, as is addressing drug therapy side effects and toxicity.

    The U.S. Department of Health and Human Services (DHHS) Panel on Antiretroviral Guidelines for Adults and Adolescents as well as WHO recommend that all individuals diagnosed with HIV receive treatment as soon as possible, including pregnant women. With advances in treatment, individuals with HIV are living longer, healthier lives. Once you begin treatment, it is important that you continue it for the rest of your life to help maintain health and prevent spread of HIV. Interruptions in treatment can lead to increases in the amount of virus (viral load) and can increase the risk of developing drug resistance, decrease immune function, and allow disease progression.

    Drug selection

    You may be infected with drug-susceptible and/or drug-resistant strains of HIV. Testing for drug resistance is performed when you are first diagnosed to help guide therapy. There are several classes of antiretroviral drugs used to treat HIV/AIDS. You will typically take at least three drugs from two different classes in order to stop the virus from replicating and to prevent drug-resistant strains from developing. Combinations of three or more antiretroviral drugs are referred to as highly active antiretroviral therapy or HAART. There are preferred treatment regimens, but the specific drugs given must be tailored for you and to the strain(s) of HIV that infect you.

    Medications may be evaluated and changed as necessary if you experience treatment failure, indicating the development of resistance to one or more of the drugs you are taking. Another reason treatment may be changed is if you experience significant side effects and toxicity. This may be related to your ability to absorb and break down the drug(s).

    You will need to work closely with your healthcare provider(s) throughout your lifetime to adjust your medications to your changing needs. If you develop resistance to one or more drugs or classes of drugs, your treatment can become challenging. You may need to consult with healthcare practitioners who specialize in the management of "treatment-experienced" patients. New HIV/AIDS drug treatments are continually being developed and brought into clinical use.

    For more details, read HIV Treatment Overview from HIV.gov.

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