AIDS was first reported in the United States in 1981 and has since become a major worldwide epidemic. AIDS is caused by the human immunodeficiency virus, or HIV. By killing or damaging cells of the body's immune system, HIV progressively destroys the body's ability to fight infections and certain cancers. People diagnosed with AIDS may get life-threatening diseases called opportunistic infections. These infections are caused by microbes such as viruses or bacteria that usually do not make healthy people sick.
Since 1981, more than 980,000 cases of AIDS have been reported in the United States to the Centers for Disease Control and Prevention (CDC). According to CDC, more than 1,000,000 Americans may be infected with HIV, one-quarter of whom are unaware of their infection. The epidemic is growing most rapidly among minority populations and is a leading killer of African-American males ages 25 to 44. According to CDC, AIDS affects nearly seven times more African Americans and three times more Hispanics than whites. In recent years, an increasing number of African-American women and children are being affected by HIV/AIDS.
Of the estimated 1.1 million Americans currently living with HIV, 21 percent do not know they are infected. People who have been infected recently with HIV often have few to no symptoms yet are extremely infectious and may unknowingly transmit the virus to others. Therefore, the Centers for Disease Control and Prevention (CDC) recommends HIV testing for adults, adolescents, and pregnant women during routine medical care. Regular HIV screenings allow healthcare providers to identify people who are not aware that they are infected with HIV, so that they can be counseled on the need to avoid high-risk behaviors, instructed on safe-sex practices, and given information about starting antiretroviral therapy. HIV testing can also be performed anonymously if a person is concerned about confidentiality.
Types of Tests
Healthcare providers can test a sample of blood to see if it contains human antibodies (disease-fighting proteins) specific to HIV. The two key types of HIV antibody tests are the enzyme-linked immunosorbent assay (ELISA) and the Western blot.
However, these antibody tests may not detect HIV antibodies in someone who has been recently infected with HIV (within 1 to 3 months of infection). In these situations, healthcare providers can test the blood for the presence of HIV genetic material. This test is extremely critical for identifying recently infected people who are at risk for unknowingly infecting others with HIV.
Testing in Infants
CDC recommends that all pregnant women get tested for HIV before and/or during delivery. Knowing the HIV status of the mother allows physicians to prevent mother-to-child HIV transmission by providing antiretroviral treatment to both mothers infected with HIV and their newborn infants. However, it is difficult to determine if a baby born to a mother infected with HIV is actually infected because babies carry their mothers’ HIV antibodies for several months. Today, healthcare providers can conduct an HIV test for infants between ages 3 months and 15 months. Researchers are now evaluating several blood tests to determine which ones are suitable for testing babies younger than 3 months.
Each of these symptoms can be related to other illnesses. The only way to find out if you are infected with HIV is to get tested.
HIV destroys CD4 positive (CD4+) T cells, which are white blood cells crucial to maintaining the function of the human immune system. As HIV attacks these cells, the person infected with the virus is less equipped to fight off infection and disease, ultimately resulting in the development of AIDS.
Most people who are infected with HIV can carry the virus for years before developing any serious symptoms. But over time, HIV levels increase in the blood while the number of CD4+ T cells decline. Antiretroviral medicines can help reduce the amount of virus in the body, preserve CD4+ T cells and dramatically slow the destruction of the immune system.
People who are not infected with HIV and generally are in good health have roughly 800 to 1,200 CD4+ T cells per cubic millimeter (mm3) of blood. Some people who have been diagnosed with AIDS have fewer than 50 CD4+ T cells in their entire body.
Stages of HIV
Within 2 to 4 weeks after infection with HIV, you may feel sick with flu-like symptoms. This is called acute retroviral syndrome (ARS) or primary HIV infection, and it’s the body’s natural response to the HIV infection. (Not everyone develops ARS, however—and some people may have no symptoms.)
During this period of infection, large amounts of HIV are being produced in your body. The virus uses important immune system cells called CD4 cells to make copies of itself and destroys these cells in the process. Because of this, the CD4 count can fall quickly.
Your ability to spread HIV is highest during this stage because the amount of virus in the blood is very high.
Eventually, your immune response will begin to bring the amount of virus in your body back down to a stable level. At this point, your CD4 count will then begin to increase, but it may not return to pre-infection levels.
This period is sometimes called asymptomatic HIV infection or chronic HIV infection. During this phase, HIV is still active, but reproduces at very low levels. You may not have any symptoms or get sick during this time. People who are on antiretroviral therapy (ART) may live with clinical latency for several decades. For people who are not on ART, this period can last up to a decade, but some may progress through this phase faster. It is important to remember that you are still able to transmit HIV to others during this phase even if you are treated with ART, although ART greatly reduces the risk. Toward the middle and end of this period, your viral load begins to rise and your CD4 cell count begins to drop. As this happens, you may begin to have symptoms of HIV infection as your immune system becomes too weak to protect you.
This is the stage of infection that occurs when your immune system is badly damaged and you become vulnerable to infections and infection-related cancers called opportunistic illnesses. When the number of your CD4 cells falls below 200 cells per cubic millimeter of blood (200 cells/mm3), you are considered to have progressed to AIDS. (Normal CD4 counts are between 500 and 1,600 cells/mm3.) You can also be diagnosed with AIDS if you develop one or more opportunistic illnesses, regardless of your CD4 count. Without treatment, people who are diagnosed with AIDS typically survive about 3 years. Once someone has a dangerous opportunistic illness, life expectancy without treatment falls to about 1 year. People with AIDS need medical treatment to prevent death.
HIV Risk Factors
HIV is found in the blood, semen, or vaginal fluid of someone who is infected with the virus. You may be at increased risk of becoming infected with HIV if you:
Currently, there is no vaccine to prevent HIV infection nor is there a cure for HIV/AIDS. To reduce your risk of becoming infected with HIV or transmitting the virus to others:
There are six major types of drugs used to treat HIV/AIDS. Called antiretrovirals because they act against the retrovirus HIV, these drugs are grouped by how they interfere with steps in HIV replication.
Entry Inhibitors interfere with the virus' ability to bind to receptors on the outer surface of the cell it tries to enter. When receptor binding fails, HIV cannot infect the cell.
Fusion Inhibitors interfere with the virus’s ability to fuse with a cellular membrane, preventing HIV from entering a cell.
Reverse Transcriptase Inhibitors prevent the HIV enzyme reverse transcriptase (RT) from converting single-stranded HIV RNA into double-stranded HIV DNA―a process called reverse transcription. There are two types of RT inhibitors:
Integrase Inhibitors block the HIV enzyme integrase, which the virus uses to integrate its genetic material into the DNA of the cell it has infected.
Protease Inhibitors interfere with the HIV enzyme called protease, which normally cuts long chains of HIV proteins into smaller individual proteins. When protease does not work properly, new virus particles cannot be assembled.
Multi-class Combination Products combine HIV drugs from two or more classes, or types, into a single product.
To prevent strains of HIV from becoming resistant to a type of antiretroviral drug, healthcare providers recommend that people infected with HIV take a combination of antiretroviral drugs in an approach called highly active antiretroviral therapy (HAART). Developed by NIAID-supported researchers, HAART combines drugs from at least two different classes.
Adherence to treatment
People infected with HIV who take antiretroviral treatments sometimes find it difficult to adhere to their drug regimens. This may be because it can be hard to take several medicines each day and at different times or because of the unpleasant side effects caused by some medicines, such as nausea and vomiting.
However, when patients fail to take their medicines, HIV has an opportunity to create more variations of itself, including strains that are resistant to antiretroviral drugs. Therefore, it is important for patients to continue taking their medicines as prescribed by their healthcare providers.
AZT (zidovudine) and AIDS
Although some people maintain that treatment with zidovudine (AZT) has compounded the AIDS epidemic, published reports of both placebo-controlled clinical trials and observational studies provide data to the contrary.
In patients with symptomatic HIV disease, for whom a beneficial effect is measured in months, AZT appears to slow disease progression and prolong life, according to double-blind, placebo-controlled clinical studies. A clinical trial known as BW 002 compared AZT with placebo in 282 patients with AIDS or advanced signs or symptoms of HIV disease. In this study, which led to the approval of AZT by the Food and Drug Administration (FDA), only one of 145 patients treated with AZT died compared with 19 of 137 placebo recipients in a six month period. Opportunistic infections occurred in 24 AZT recipients and 45 placebo recipients. In addition to reducing mortality, AZT was shown to have reduced the frequency and severity of AIDS-associated opportunistic infections, improved body weight, prevented deterioration in Karnofsky performance score, and increased counts of CD4+ T lymphocytes in the peripheral blood. Continued follow-up in 229 of these patients showed that the survival benefit of AZT extended to at least 21 months after the initiation of therapy; survival in the original treatment group was 57.6 percent at that time, whereas survival among members of the original placebo group was 51.5 percent at nine months.
In another placebo-controlled study known as ACTG 016, which enrolled 711 symptomatic HIV-infected patients with CD4+ T cell counts between 200 and 500 cells/mm3, those taking AZT were less likely to experience disease progression than those on placebo during a median study period of 11 months. In this study, no difference in disease progression was noted among participants who began the trial with CD4+ T cell counts greater than 500/mm3.
A Veteran's Administration study of 338 individuals with early symptoms of HIV disease and CD4+ T cell counts between 200 and 500 cells/mm3 found that immediate therapy significantly delayed disease progression compared with deferred therapy, but did not lengthen (or shorten) survival after an average study period of more than two years.
Among asymptomatic HIV-infected individuals, several placebo-controlled clinical trials suggest that AZT can delay disease progression for 12 to 24 months but ultimately does not increase survival. Significantly, long-term follow-up of persons participating in these trials, although not showing prolonged benefit of AZT, has never indicated that the drug increases disease progression or mortality. The lack of excess AIDS cases and death in the AZT arms of these large trials effectively rebuts the argument that AZT causes AIDS.
During a 4.5 year follow-up period (mean 2.6 years) of a trial known as ACTG 019, no differences were seen in overall survival between AZT and placebo groups among 1,565 asymptomatic patients entering the study with fewer than 500 CD4+ T cells/mm3. In that study, AZT was superior to placebo in delaying progression to AIDS or advanced ARC for approximately one year, and a more prolonged benefit was seen among a subset of patients.
Antiretroviral drugs can, in rare cases, cause serious medical complications, including metabolic changes such as abnormal fat distribution, abnormal lipid and glucose metabolism, and bone loss. Monitoring for these complications and side effects is the responsibility of patients and their healthcare providers.
NIAID supports research aimed at understanding antiretroviral drug-related complications and other side effects, as well as strategies to reduce patient exposure to potentially toxic drug regimens, such as different drug-dosing schedules or combinations, and comparing early versus delayed treatment. NIAID is working to develop simpler, less toxic, and more effective antiretroviral drug regimens.
National Institute of Allergy and Infectious Diseases. Understanding HIV/AIDS. Published January 31, 2011.