Human immunodeficiency virus (HIV) facts

    • HIV is the virus that causes HIV infection and the acquired immunodeficiency syndrome (AIDS).
    • Anal or vaginal sexual intercourse and illicit injectable drug use commonly transmit HIV. Infected mothers may also transmit HIV to their child during pregnancy orbreastfeeding. Less common routes of transmission include needle-stick injuries or exposure to contaminated blood.
    • The blood supply in the United States is tested for HIV before use, and statistics show the risk of acquiring HIV infection from a transfusion is less than one in 1.5 million.
    • HIV attacks the immune system, especially cells known as CD-4 lymphocytes. Serious impairment of the CD-4 lymphocytes makes people susceptible to specific infections and cancers.
    • Untreated HIV infected progresses through three stages, with stage three being AIDS.
    • Health-care professionals diagnose HIV with tests that measure antibodies against the virus or measure the virus directly.
    • Treatment with highly active antiretroviral therapy (HAART or ART) dramatically increases life expectancy although it does not cure HIV infection.



    Approximately 50,000 new HIV infections occur in the United States each year. In the U.S., HIV is spread mainly by:

    Having sex with someone who has HIV. In general:

    Anal sex (penis in the anus of a man or woman) is the highest-risk sexual behavior. Receptive anal sex (“bottoming”) is riskier than insertive anal sex (“topping”).

    Vaginal sex (penis in the vagina) is the second highest-risk sexual behavior.

    Having multiple sex partners or having sexually transmitted infections can increase the risk of HIV infection through sex.

    Sharing needles, syringes, rinse water, or other equipment (“works”) used to prepare injection drugs with someone who has HIV.

    Less commonly, HIV may be spread by:

    Being born to an infected mother. HIV can be passed from mother to child during pregnancy, birth, or breastfeeding.

    Being stuck with an HIV-contaminated needle or other sharp object. This is a risk mainly for health care workers.

    Receiving blood transfusions, blood products, or organ/tissue transplants that are contaminated with HIV. This risk is extremely small because of rigorous testing of the US blood supply and donated organs and tissues.

    Eating food that has been pre-chewed by an HIV-infected person. The contamination occurs when infected blood from a caregiver’s mouth mixes with food while chewing, and is very rare.

    Being bitten by a person with HIV. Each of the very small number of documented cases has involved severe trauma with extensive tissue damage and the presence of blood. There is no risk of transmission if the skin is not broken.

    Oral sex—using the mouth to stimulate the penis, vagina, or anus (fellatio, cunnilingus, and rimming). Giving fellatio (mouth to penis oral sex) and having the person ejaculate (cum) in your mouth is riskier than other types of oral sex.

    Contact between broken skin, wounds, or mucous membranes and HIV-infected blood or blood-contaminated body fluids. These reports have also been extremely rare.

    Deep, open-mouth kissing if the person with HIV has sores or bleeding gums and blood is exchanged. HIV is not spread through saliva. Transmission through kissing alone is extremely rare.

    HIV is NOT spread by:

    Air or water

    Insects, including mosquitoes or ticks

    Saliva, tears, or sweat

    Casual contact, like shaking hands, hugging or sharing dishes/drinking glasses

    Drinking fountains

    Toilet seats

    HIV is not spread through the air and it does not live long outside the human body.

    Having an undetectable viral load greatly lowers the chance that a person living with HIV can transmit the virus to a partner, but there is still some risk. “Viral load” refers to the amount of HIV in an infected person’s blood. An “undetectable viral load” is when the amount of HIV in a person’s blood is so low that it can’t be measured. antiretroviral therapy (ART) reduces a person’s viral load, ideally to an undetectable level, when taken consistently and correctly. However, a person with HIV can still potentially transmit HIV to a partner even if they have an undetectable viral load, because:

    HIV may still be found in a person’s genital fluids (e.g., semen, vaginal fluids). The viral load test only measures virus in a person’s blood.

    A person’s viral load may go up between tests. When this happens, they may be more likely to transmit HIV to partners.

    Sexually transmitted diseases (STDs) increase viral load in a person’s genital fluids



    The terms “HIV” and “AIDS” can be confusing because both terms refer to the same disease.

    However, “HIV” refers to the virus itself, and “AIDS” refers to the late stage of HIV infection, when an HIV-infected person’s immune system is severely damaged and has difficulty fighting diseases and certain cancers. Before the development of certain medications, people with HIV could progress to AIDS in just a few years. But today, most people who are HIV-positive do not progress to AIDS.

    That’s because if you have HIV and you take antiretroviral therapy (ART) consistently, you can keep the level of HIV in your body low. This will help keep your body strong and healthy and reduce the likelihood that you will ever progress to AIDS. It will also help lower your risk of transmitting HIV to others.


    As the virus continues to multiply and destroy immune cells, you may develop mild infections or chronic signs and symptoms such as:
    • Fever.
    • Fatigue.
    • Swollen lymph nodes — often one of the first signs of HIV infection.
    • Diarrhea.
    • Weight loss.
    • Cough.
    • Shortness of breath.


    Many people do not develop symptoms after getting infected with HIV. Others have a flu-like illness within several days to weeks after exposure to the virus. They complain of fever, headache, tiredness, and enlarged lymph glands in the neck. These symptoms usually disappear on their own within a few weeks.

    • Following initial infection, you may have no symptoms. The progression of disease varies widely among individuals. This state may last from a few months to more than 10 years.
      • During this period, the virus continues to multiply actively and infects and kills the cells of the immune system. The immune system allows us to fight against the bacteria, viruses, and other infectious causes.
      • The virus destroys the cells that are the primary infection fighters, called CD4+ or T4 cells.
    • Once the immune system weakens, a person infected with HIV can develop the following symptoms:

    AIDS is the most advanced stage of HIV infection. The definition of AIDS includes all HIV-infected people who have fewer than 200 CD4+ cells per microliter of blood. The definition also includes 26 conditions that are common in advanced HIV disease but that rarely occur in healthy people. Most of these conditions are infections caused by bacteria, viruses, fungi, parasites, and other organisms. Opportunistic infections are common in people with AIDS. Nearly every organ system is affected. Some of the common symptoms include the following:

    People with AIDS are prone to develop various cancers such as Kaposi sarcomacervical cancer, and cancers of the immune system known as lymphomas. Kaposi sarcoma causes round, brown, reddish or purple spots that develop in the skin or in the mouth. After the diagnosis of AIDS is made, the average survival time has been estimated to be 2-3 years.


    What are the different stages of an HIV infection?

    Untreated infection with HIV progresses over time and gradually impairs specific parts of the immune system, especially by destroying the white blood cells known as CD4 lymphocyte cells. This progression is described as occurring in stages. All stages require laboratory confirmation of HIV infection.

    There are multiple different staging systems. For example, the Centers for Disease Control and Prevention case definition uses a staging system based on how much damage has been done to the immune system:

    • Stage 1 disease is the earliest phase. Stage 1 has no unusual infections or cancers or other conditions that would be associated with AIDS. In other words, stage 1 disease has no "AIDS-defining conditions" (see below). Although blood tests are positive for HIV, the CD4 cell count is at least 500 cells per microliter of blood (or >29% of all lymphocytes).
    • Stage 2 disease occurs when the CD4 count is between 200-499 cells per microliter (14%-28% of all lymphocytes), but again there are no AIDS-defining conditions present.
    • Stage 3 disease is synonymous with AIDS and is the most severe stage. There are two ways of diagnosing stage 3 disease: either by CD4 counts below 200 cells per microliter (<14% of lymphocytes) or through documentation of an AIDS-defining condition.

    Another way to conceptualize HIV is according to the characteristics or clinical manifestations: acute infection, clinical latency, or AIDS.

    • Acute infection: Two to four weeks after infection with HIV, the patient can experience an acute illness, often described as "the worst flu ever." This is called acute retroviral syndrome (ARS) or primary HIV infection, and it is caused by the body's natural response to the HIV infection. Not all newly infected people develop ARS, however -- and it can take up to three months for it to appear. During this period of infection, large amounts of virus are being produced. The virus uses CD4 cells to replicate and destroys them in the process. Because of this, the CD4 count can fall rapidly. Eventually, the immune response will begin to bring the level of virus in the body back down to a level called a "viral set point," which is a relatively stable level of virus in the body. At this point, the CD4 count begins to increase, but it may not return to pre-infection levels. The human immune response suppresses the virus but does not eliminate it from the body.
    • Clinical latency: After the acute stage of HIV infection, the disease moves into a stage called clinical latency. This period is sometimes called asymptomatic HIV infection or chronic HIV infection. During this phase, HIV reproduces at very low levels, although it is still active. In this state, infected people may be able to maintain an undetectable viral load and a healthy CD4 cell count without the use of medication for a time. There are usually few if any symptoms. This period can last up to eight years or longer. However, some people progress through this phase faster than others. It is important to remember that people are still able to transmit HIV to others during this phase. Toward the middle and end of this period, the viral load begins to rise and the CD4 cell count begins to drop. As this happens, infected people may begin to have constitutional symptoms such as fatigue and other nonspecific symptoms.
    • AIDS: As the number of CD4 cells falls below 200 cells per cubic millimeter of blood (200 cells/cubic milliliter), people will be diagnosed as having AIDS. Normal CD4 counts are between 500 and 1,600 cells per cubic milliliter. This is the stage of infection that occurs when the immune system is badly damaged and patients become vulnerable to opportunistic infections. Without treatment, people who are diagnosed with AIDS typically survive about three years. Once someone has a dangerous opportunistic infection, life expectancy falls to about one year.

     AIDS-defining conditions in an HIV-infected person include the following:

    • Candidiasis of bronchi, trachea, lungs, or esophagus
    • Cervical cancer, invasive
    • Disseminated or extrapulmonary coccidioidomycosis or Cryptococcus
    • Chronic intestinal cryptosporidiosis or isosporiasis
    • Cytomegalovirus disease of the retina or an unusual site (other than liver, spleen, or nodes)
    • HIV encephalopathy
    • Herpes simplex that does not heal or that occurs in the lungs or esophagus
    • Histoplasmosis that is disseminated or extrapulmonary
    • Kaposi's sarcoma
    • Lymphoid interstitial pneumonia and/or pulmonary lymphoid hyperplasia*
    • Selected lymphomas including Burkitt's, immunoblastic, or arising in the brain
    • Disseminated or extrapulmonary Mycobacterium avium-intracellularecomplex or Mycobacterium kansasii, or other species of mycobacterium
    • Mycobacterium tuberculosis infection
    • Pneumocystis jirovecii pneumonia
    • Recurrent bacterial pneumonia
    • Progressive multifocal leukoencephalopathy
    • Recurrent or multiple bacterial infections
    • Recurrent Salmonella septicemia
    • Toxoplasmosis of brain
    • Wasting syndrome associated with HIV infection


    Table 2. WHO Clinical Staging of HIV/AIDS for Adults and Adolescents
    Clinical Stage Clinical Conditions or Symptoms
    Primary HIV Infection
    • Asymptomatic
    • Acute retroviral syndrome
    Clinical Stage 1
    • Asymptomatic
    • Persistent generalized lymphadenopathy
    Clinical Stage 2
    • Moderate unexplained weight loss (<10% of presumed or measured body weight)
    • Recurrent respiratory infections (sinusitis, tonsillitis, otitis media, and pharyngitis)
    • Herpes zoster
    • Angular cheilitis
    • Recurrent oral ulceration
    • Papular pruritic eruptions
    • Seborrheic dermatitis
    • Fungal nail infections
    Clinical Stage 3
    • Unexplained severe weight loss (>10% of presumed or measured body weight)
    • Unexplained chronic diarrhea for >1 month
    • Unexplained persistent fever for >1 month (>37.6°C, intermittent or constant)
    • Persistent oral candidiasis (thrush)
    • Oral hairy leukoplakia
    • Pulmonary tuberculosis (current)
    • Severe presumed bacterial infections (e.g., pneumonia, empyema, pyomyositis, bone or joint infection, meningitis, bacteremia)
    • Acute necrotizing ulcerative stomatitis, gingivitis, or periodontitis
    • Unexplained anemia (hemoglobin
    • Neutropenia (neutrophils
    • Chronic thrombocytopenia (platelets <50,000 cells/µL)
    Clinical Stage 4
    • HIV wasting syndrome, as defined by the CDC (see Table 1, above)
    • Pneumocystis pneumonia
    • Recurrent severe bacterial pneumonia
    • Chronic herpes simplex infection (orolabial, genital, or anorectal site for >1 month or visceral herpes at any site)
    • Esophageal candidiasis (or candidiasis of trachea, bronchi, or lungs)
    • Extrapulmonary tuberculosis
    • Kaposi sarcoma
    • Cytomegalovirus infection (retinitis or infection of other organs)
    • Central nervous system toxoplasmosis
    • HIV encephalopathy
    • Cryptococcosis, extrapulmonary (including meningitis)
    • Disseminated nontuberculosis mycobacteria infection
    • Progressive multifocal leukoencephalopathy
    • Candida of the trachea, bronchi, or lungs
    • Chronic cryptosporidiosis (with diarrhea)
    • Chronic isosporiasis
    • Disseminated mycosis (e.g., histoplasmosis, coccidioidomycosis, penicilliosis)
    • Recurrent nontyphoidal Salmonella bacteremia
    • Lymphoma (cerebral or B-cell non-Hodgkin)
    • Invasive cervical carcinoma
    • Atypical disseminated leishmaniasis
    • Symptomatic HIV-associated nephropathy
    • Symptomatic HIV-associated cardiomyopathy
    • Reactivation of American trypanosomiasis (meningoencephalitis or myocarditis)



    CD4 counts and infections


    The weaker your immune system, the more likely you are to get an opportunistic infection.

    In general, here's how a CD4 count relates to your risk of OIs:


    Above 500 CD4 cells
    No unusual infections are likely to occur.


    200-500 CD4 cells
    There is an increased risk for certain infections, such as shingles, thrush, skin infections, bacterial sinus and lung infections, and TB.


    There is an increased risk for PCP (pneumonia), and you should begin treatment to prevent it.


    If counts are below 100, preventive treatment should begin for MAC and toxoplasmosis (if not already on PCP prophylaxis that helps prevent toxoplasmosis, like trimethoprim/sulfamethoxazole).


    There is an increased risk for cytomegalovirus



    What is the prognosis of an HIV infection? 

    how long can a HIV patient survive if he takes HIV treatment?


    Without treatment, HIV infection progresses to AIDS in approximately 10 years, with death following within three years after onset of AIDS. With appropriate treatment, a 20-year-old with HIV infection can expect to live to reach 71 years of age. This dramatic increase in life expectancy emphasizes the need for early diagnosis and treatment. Moreover, with newer treatment regimens and guidelines, there is every reason to think that life expectancy will continue to increase in patients who are able to receive appropriate treatment. There are some factors that decrease life expectancy, including use of illicit drugs and the