AIDS is a chronic, life-threatening condition caused by the human immunodeficiency virus (HIV). By damaging your immune system, HIV interferes with your body's ability to fight off viruses, bacteria and fungi that cause disease.

What is it?

  • AIDS is a chronic, life-threatening condition caused by the human immunodeficiency virus (HIV). By damaging your immune system, HIV interferes with your body's ability to fight off viruses, bacteria and fungi that cause disease. HIV makes you more susceptible to certain types of cancers and to infections your body would normally resist, such as pneumonia and meningitis. The virus and the infection itself are known as HIV. "Acquired immunodeficiency syndrome (AIDS)" is the name given to the later stages of an HIV infection.
  • An estimated 39.5 million people have HIV worldwide. And though the spread of the virus has slowed in some countries, it has escalated or remained unchanged in others. The best hope for stemming the spread of HIV lies in prevention, treatment and education.


The symptoms of HIV and AIDS vary, depending on the phase of infection.

Early infection

When first infected with HIV, you may have no signs or symptoms at all, although it's more common to develop a brief flu-like illness two to four weeks after becoming infected. Signs and symptoms may include:

Even if you don't have symptoms, you're still able to transmit the virus to others. Once the virus enters your body, your own immune system also comes under attack. The virus multiplies in your lymph nodes and slowly begins to destroy your helper T cells (CD4 lymphocytes) — the white blood cells that coordinate your entire immune system.

Later infection

You may remain symptom-free for eight or nine years or more. But as the virus continues to multiply and destroy immune cells, you may develop mild infections or chronic symptoms such as:

  • Swollen lymph nodes — often one of the first signs of HIV infection
  • Diarrhoea
  • Weight loss
  • Fever
  • Cough and shortness of breath

Latest phase of infection

During the last phase of HIV — which occurs approximately 10 or more years after the initial infection — more serious symptoms may begin to appear, and the infection may then meet the official definition of AIDS. In 1993, the Centers for Disease Control and Prevention (CDC) redefined AIDS to mean the presence of HIV infection as shown by a positive HIV-antibody test plus at least one of the following:

  • The development of an opportunistic infection — an infection that occurs when your immune system is impaired — such as Pneumocystis carinii pneumonia (PCP)
  • A CD4 lymphocyte count of 200 or less — a normal count ranges from 800 to 1,200

By the time AIDS develops, your immune system has been severely damaged, making you susceptible to opportunistic infections. The signs and symptoms of some of these infections may include:

  • Soaking night sweats
  • Shaking chills or fever higher than 100 F (38 C) for several weeks
  • Dry cough and shortness of breath
  • Chronic diarrhea
  • Persistent white spots or unusual lesions on your tongue or in your mouth
  • Headaches
  • Blurred and distorted vision
  • Weight loss

You may also begin to experience signs and symptoms of later stage HIV infection itself, such as:

  • Persistent, unexplained fatigue
  • Soaking night sweats
  • Shaking chills or fever higher than 100 F (38 C) for several weeks
  • Swelling of lymph nodes for more than three months
  • Chronic diarrhea
  • Persistent headaches

If you're infected with HIV, you're also more likely to develop certain cancers, especially Kaposi's sarcoma, cervical cancer and lymphoma, although improved treatments have reduced the risk of these illnesses.

Symptoms of HIV in children

Children who are HIV-positive may experience:

  • Difficulty gaining weight
  • Difficulty growing normally
  • Problems walking
  • Delayed mental development
  • Severe forms of common childhood illnesses such as ear infections (otitis media), pneumonia and tonsillitis 


Normally, white blood cells and antibodies attack and destroy foreign organisms that enter your body. This response is coordinated by white blood cells known as CD4 lymphocytes. These lymphocytes are also the main targets of HIV, which attaches to the cells and then enters them. Once inside, the virus inserts its own genetic material into the lymphocytes and makes copies of 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. In the meantime, the old host cells and some uninfected CD4 cells die from the effects of the virus. The cycle repeats itself again and again. In the process, billions of new HIV particles are produced every day. Eventually, the number of CD4 cells in the body decreases, leading to severe immune deficiency, which means your body can no longer effectively fight off viruses and bacteria that cause disease.

How HIV is transmitted

You can become infected with HIV in several ways, including:

  • Sexual transmission. You may become infected if you have vaginal, anal or oral sex with an infected partner whose blood, semen or vaginal secretions enter your body. You can also become infected from shared sexual devices if they're not washed or covered with a condom. The virus is present in the semen or vaginal secretions of someone who's infected and enters your body through small tears that can develop in the vagina or rectum during sexual activity. If you already have another sexually transmitted disease, you're at much greater risk of contracting HIV. Contrary to what researchers once believed, women who use the spermicide nonoxynol 9 also may be at increased risk. This spermicide irritates the lining of the vagina and may cause tears that allow the virus into the body.
  • Transmission through infected blood. In some cases, the virus may be transmitted through blood and blood products that you receive in blood transfusions. Since 1985, American hospitals and blood banks have screened the blood supply for HIV antibodies. This blood testing, along with improvements in donor screening and recruitment practices, has substantially reduced the risk of acquiring HIV through a transfusion.
  • Transmission through needle sharing. HIV is easily transmitted through needles and syringes contaminated with infected blood. Sharing intravenous drug paraphernalia puts you at high risk of HIV and other infectious diseases such as hepatitis. Your risk is greater if you inject drugs frequently and also engage in high-risk sexual behavior. Avoiding the use of injected drugs is the most reliable way to prevent infection. If that isn't an option, you can reduce your risk by participating in a needle exchange program that allows you to trade used needles and syringes for sterile ones.
  • Transmission through accidental needle sticks. Transmission of the virus between HIV-positive people and health care workers through needle sticks is low. Experts put the risk at far less than 1 percent.
  • Transmission from mother to child. Each year, nearly 600,000 infants are infected with HIV, either during pregnancy or delivery or through breast-feeding. But if women receive treatment for HIV infection during pregnancy, the risk to their babies is significantly reduced. When medications aren't available, Caesarean section is sometimes recommended instead of vaginal delivery. Other options, such as vaginal disinfection, haven't proved effective.
  • Other methods of transmission. In rare cases, the virus may be transmitted through organ or tissue transplants or unsterilized dental or surgical equipment.

Ways HIV is not transmitted

To become infected with HIV, infected blood, semen or vaginal secretions must enter your body. You can't become infected through ordinary contact — hugging, kissing, dancing or shaking hands — with someone who has HIV or AIDS. 

Risk factors

Anyone of any age, race, sex or sexual orientation can be infected with HIV, but you're at greatest risk of HIV/AIDS if you:

  • Have unprotected sex with multiple partners. You're at risk whether you're heterosexual, homosexual or bisexual. Unprotected sex means having sex without using a new latex or polyurethane condom every time.
  • Have unprotected sex with someone who is HIV-positive.
  • Have another sexually transmitted disease, such as syphilis, herpes, chlamydia, gonorrhea or bacterial vaginosis.
  • Share needles during intravenous drug use.
  • Received a blood transfusion or blood products before 1985.
  • Have fewer copies of a gene called CCL3L1 that helps fight HIV infection.

Newborns or nursing infants whose mothers tested positive for HIV but did not receive treatment also are at high risk.


HIV infection weakens your immune system, making you highly susceptible to a large number of bacterial, viral, fungal and parasitic infections. You may also be vulnerable to certain types of cancers. But treatment with anti-retroviral drugs has markedly decreased the number of opportunistic infections and cancers affecting people with HIV. It's now more likely these infections will occur in people who have not had treatment.

Bacterial infections

  • Bacterial pneumonia. Dozens of types of bacteria can cause bacterial pneumonia, which may develop on its own or after you've had an upper respiratory infection such as a cold or the flu.
  • Mycobacterium avium complex (MAC). This infection is caused by a group of mycobacteria referred to by a single name — MAC. The mycobacteria normally cause an infection of the respiratory tract. But if you have advanced HIV infection and your CD4 lymphocyte count is less than 50, you're more likely to develop a systemic infection that can affect almost any internal organ, including your bone marrow, liver or spleen. MAC causes nonspecific symptoms such as fever, night sweats, weight loss, stomach pain and diarrhea.
  • Tuberculosis (TB). In resource-poor nations, TB is the most common opportunistic infection associated with HIV and a leading cause of death among people living with AIDS. Millions of people are currently infected with both HIV and tuberculosis, and many experts consider the two diseases twin epidemics. That's because HIV/AIDS and TB have a deadly symbiotic relationship, in which each fuels the progress of the other. Having HIV makes you more susceptible to TB and far more likely to progress from dormant to active HIV infection. At the same time, TB increases the rate at which the AIDS virus replicates. What's more, TB often strikes people with HIV years before other problems associated with HIV develop. One of the first indications of HIV infection may be the sudden onset of TB — often in a site outside the lungs. If you're HIV-positive, you should have a simple skin test for TB early in your medical care. If the test is positive, you'll also need a chest X-ray and other appropriate tests to make sure you don't have an active infection. If your TB isn't active, there are treatments to prevent it from becoming active. TB is more worrisome than many other opportunistic infections because it's highly contagious. Multidrug-resistant tuberculosis, in which the disease resists treatment with traditional antibiotics, is of particular concern to people with HIV/AIDS.
  • Salmonellosis. You contract this bacterial infection from contaminated food or water. Symptoms include severe diarrhea, fever, chills, abdominal pain and, occasionally, vomiting. Although anyone exposed to salmonella bacteria can become sick, salmonellosis is far more common in people who are HIV-positive. You can reduce your risk by washing your hands carefully after handling food and animals and by cooking meat and eggs thoroughly.
  • Bacillary angiomatosis. This infection, caused by Bartonella henselae bacteria, first appears as purplish to bright red patches on your skin. It often resembles Kaposi's sarcoma, but it can cause disease in other parts of your body, including your liver and spleen.

Viral infections

  • Cytomegalovirus (CMV). This common herpesvirus is transmitted in body fluids such as saliva, blood, urine, semen and breast milk. But a healthy immune system inactivates the virus, and it remains dormant in your body. If your immune system weakens, the virus resurfaces, causing damage to your eyes, digestive tract, lungs or other organs. Most commonly, CMV causes infection and inflammation of your retina (CMV retinitis). If not treated, CMV retinitis can lead to blindness.
  • Viral hepatitis. Viral hepatitis is a viral infection of the liver. Signs and symptoms include yellowing of your skin and the whites of your eyes (jaundice), fatigue, nausea, abdominal pain, loss of appetite and diarrhea. There are several types of viral hepatitis, but the most common are hepatitis A, B and C. Hepatitis B and C can lead to persistent or chronic infection and put you at risk of long-term complications such as cirrhosis or liver cancer. If you are HIV-positive and also have hepatitis, you may be more likely to develop liver toxicity from your medications.
  • Herpes simplex virus (HSV). HSV, which usually causes genital herpes, may be transmitted during unprotected anal or vaginal sex. Initial symptoms include pain or irritated skin in the genital area. Later, sores that ooze and bleed erupt on the genitals, buttocks and anus. Although these sores eventually heal, the virus periodically reappears, causing the same symptoms. If you have HIV, your skin infection is likely to be more severe than it would be in people who don't have HIV, and the sores may take longer to heal. Systemic symptoms may also be more severe. Although the herpes virus isn't life-threatening in adults, it may cause brain damage and blindness.
  • Human papillomavirus (HPV). This is one of the most common causes of sexually transmitted disease. Some types of this virus cause common warts. Other types cause warts on the genitals. If you're HIV-positive, you're especially susceptible to infection with HPV and more prone to recurrent infections. HPV infection is especially serious because it significantly increases a woman's risk of cervical cancer. Infection with both HPV and HIV increases a woman's risk even further — cervical cancer seems to occur more often and more aggressively in women who are HIV-positive. In 2006, the Food and Drug Administration approved the first vaccine to offer protection from the most dangerous types of HPV. The vaccine is most effective when given to girls before they become sexually active, but it also provides protection for sexually active women age 26 and younger. If you are not a candidate for the vaccine, are HIV-positive or have unprotected sex with more than one partner, you should have a Pap test — a test that examines cells taken from the cervix — every year to check for cervical cancer, HPV and other sexually transmitted diseases. Anyone who engages in anal sex should be tested for anal cancer because HPV increases the risk of this type of cancer in both men and women.
  • Progressive multifocal leukoencephalopathy (PML). PML is an extremely serious brain infection caused by the human polyomavirus JC virus. Signs and symptoms vary and may include speech problems, weakness on one side of the body, loss of vision in one eye, or numbness in one arm or leg. PML usually occurs only when your immune system has been severely damaged.

Fungal infections

  • Candidiasis. Candidiasis is a common HIV-related infection. It causes inflammation and a thick white coating on the mucous membranes of your mouth, tongue (thrush), esophagus (Candida esophagitis) or vagina. Children may have especially severe symptoms in the mouth or esophagus, which can make eating painful and difficult.
  • Cryptococcal meningitis. Meningitis is an inflammation of the membranes and fluid surrounding your brain and spinal cord (meninges). Cryptococcal meningitis is a common central nervous system infection associated with HIV, caused by a fungus that is present in soil. It may also be associated with bird or bat droppings. Symptoms include headache, high fever, a stiff neck and sensitivity to light. Cryptococcal meningitis can be successfully treated with antifungal medications, but early treatment is essential. Meningitis is a serious disease that can cause severe complications or prove fatal in a short period of time. Once you've had cryptococcal meningitis, you'll need to be on long-term medication to prevent a recurrence.

Parasitic infections

  • Pneumocystis carinii pneumonia (PCP). Although anti-retroviral drugs have helped reduce the number of cases of PCP, it remains one of the most common opportunistic infections affecting people with AIDS in the United States. PCP attacks the lungs, making it difficult to breathe. Signs and symptoms include a cough that doesn't go away, fever and trouble breathing.
  • Toxoplasmosis. This potentially deadly infection is caused by Toxoplasma gondii, a parasite spread primarily by cats. Infected cats pass the parasites in their stool, and the parasites may then spread to other animals. Humans generally contract toxoplasmosis by touching their mouths with their hands after changing cat litter or by eating raw or undercooked meat, especially pork, lamb and venison. Once you're infected, the parasites can spread to every organ in your body, including your heart, eyes and lungs. For many people with AIDS, toxoplasmosis leads to encephalitis, an infection of the brain. Signs and symptoms may include disorientation, seizures, and difficulty walking or speaking.
  • Cryptosporidiosis. This infection is caused by an intestinal parasite that's commonly found in animals. You contract cryptosporidiosis when you ingest contaminated food or water. The parasite grows in your intestines and bile ducts, leading to severe, chronic diarrhea in people with AIDS.


  • Kaposi's sarcoma. Kaposi's sarcoma is a tumor of the blood vessel walls. Although rare in people not infected with HIV, it's common in HIV-positive people. Kaposi's sarcoma usually appears as pink, red or purple lesions on the skin and mouth. In people with darker skin, the lesions may look dark brown or black. Kaposi's sarcoma can also affect the internal organs, including the digestive tract and lungs. Researchers are testing new combinations of the chemotherapy drugs currently used to treat Kaposi's sarcoma as well as new ways of delivering those medications. What's more, as with most opportunistic infections associated with AIDS, the use of anti-retrovirals has reduced the incidence of this cancer and has even reduced the lesions in people already affected.
  • Non-Hodgkin's lymphoma. This cancer originates in lymphocytes, a type of white blood cell. Lymphocytes are concentrated in your bone marrow, lymph nodes, spleen, digestive tract and skin. Although lymphomas can start in other organs, they usually begin in your lymph nodes. The most common early sign is painless swelling of the lymph nodes in your neck, armpit or groin.

Other complications

  • Wasting syndrome. Aggressive treatment regimens have reduced the number of cases of wasting syndrome, but it does still affect many people with AIDS. It is defined as a loss of at least 10 percent of body weight and is often accompanied by diarrhea, chronic weakness and fever.
  • Neurological complications. Although AIDS doesn't appear to infect the nerve cells, it can still cause neurological symptoms such as confusion, forgetfulness, changes in behavior, depression, anxiety and trouble walking. One of the most common neurological complications is AIDS dementia complex, which leads to behavioral changes and diminished mental functioning. It's best treated with aggressive anti-retroviral medications.


HIV is diagnosed by testing your blood or oral mucus for the presence of antibodies to the virus. The Centers for Disease Control and Prevention (CDC) encourages voluntary HIV testing as a routine part of medical care for all adolescents and adults ages 13 to 64. Although the CDC says that everyone should be tested at least once, yearly testing is recommended only for people at high risk of infection.

Unfortunately, HIV tests aren't accurate immediately after infection because it takes time for you to develop these antibodies — usually about 12 weeks. In rare cases, it can take up to six months for an HIV test to become positive.

ELISA and Western blot tests

For years, the only available test for HIV was the enzyme-linked immunosorbent assay (ELISA) test that looked for antibodies to the virus in a sample of your blood. If this test was positive — meaning you had antibodies to HIV — the same test was repeated. If the repeat test was also positive for HIV antibodies, you'd then have another confirming blood test called the Western blot test, which checks for the presence of HIV proteins. The Western blot test was important because you may have non-HIV antibodies that cause a false-positive result on the ELISA test. Combining the two types of tests helped ensure that the results were accurate, and you'd receive a diagnosis of HIV only if all three tests were positive. The downside is that it can take up to two weeks to get the results of the ELISA and Western blot tests, a period of time that can take an emotional toll and that discouraged many people from returning to get their test results.

Rapid tests

Now, several rapid tests can give highly accurate information within as little as 20 minutes. These tests look for antibodies to the virus using a sample of your blood or fluids collected on a treated pad that's rubbed on your upper and lower gums. The oral test is almost as sensitive as the blood test and eliminates the need for drawing blood. A positive reaction on a rapid test requires a confirming blood test. And because the tests are relatively new and were originally approved for use only in certified laboratories, they may not be available everywhere.

Home tests

Currently, the Food and Drug Administration (FDA) has approved only one HIV test for home use. The Home Access HIV-1 test, marketed by Home Access Health, is as accurate as a clinical test, and all positive results are automatically retested.

Unlike a home pregnancy test, you don't evaluate the test yourself. Instead, you mail in a drop of your blood, then call a toll-free number to receive your results in three to seven business days. This approach ensures your privacy and anonymity — you're identified only by a code number that comes with your kit. The greatest disadvantage is that you're not offered the counseling that you typically receive in a clinic or doctor's office, although you're given referrals for medical and social services. No matter what type of test you choose, if you test positive for an HIV infection, tell your sexual partner or partners right away so that they can be screened and take steps to protect themselves.

If you receive a diagnosis of HIV/AIDS, your doctor will use a test to help predict the probable progression of your disease. This test measures the amount of virus in your blood (viral load). Studies have shown that people with higher viral loads generally fare more poorly than do those with a lower viral load. Viral load tests are also used to decide when to start and when to change your treatment.