AIDS (acquired immune deficiency syndrome) is the final and most serious stage of HIV disease, which causes severe damage to the immune system.

AIDS is the fifth leading cause of death among people aged 25 - 44 in the United States, down from number one in 1995. About 25 million people worldwide have died from this infection since the start of the epidemic, and 40.3 million people around the world are currently living with HIV/AIDS.

Human immunodeficiency virus (HIV) causes AIDS. The virus attacks the immune system and leaves the body vulnerable to a variety of life-threatening infections and cancers.

Common bacteria, yeast, parasites, and viruses that ordinarily do not cause serious disease in people with healthy immune systems can cause fatal illnesses in people with AIDS.

HIV has been found in saliva, tears, nervous system tissue and spinal fluid, blood, semen (including pre-seminal fluid, which is the liquid that comes out prior to ejaculation), vaginal fluid, and breast milk. However, only blood, semen, vaginal secretions, and breast milk generally transmit infection to others.

The virus can be transmitted:

• Through sexual contact -- including oral, vaginal, and anal sex
• Through blood -- via blood transfusions (now extremely rare in the US) or needle sharing
• From mother to child -- a pregnant woman can transmit the virus to her fetus through their shared blood circulation, or a nursing mother can transmit it to her baby in her milk

Other transmission methods are rare and include accidental needle injury, artificial insemination with infected donated semen, and organ transplantation with infected organs.

HIV infection is not spread by casual contact such as hugging, by touching items previously touched by a person infected with the virus, during participation in sports, or by mosquitoes.

It is NOT transmitted to a person who DONATES blood or organs. Those who donate organs are never in direct contact with those who receive them. Likewise, a person who donates blood is not in contact with the person receiving it. In all these procedures, sterile needles and instruments are used.

However, HIV can be transmitted to a person RECEIVING blood or organs from an infected donor. To reduce this risk, blood banks and organ donor programs screen donors, blood, and tissues thoroughly.

People at highest risk for getting HIV include:

• Intravenous drug users who share needles
• Infants born to mothers with HIV who don't receive HIV therapy during pregnancy
• People engaging in unprotected sex
• People who received blood transfusions or clotting products between 1977 and 1985 (prior to when standard screening for the virus began)
• Sexual partners of those who participate in high-risk activities (such as anal sex)

AIDS begins with HIV infection. People infected with HIV may have no symptoms for 10 years or longer, but they can still transmit the infection to others during this symptom-free period. Meanwhile, if the infection is not detected and treated, the immune system gradually weakens, and AIDS develops.

Acute HIV infection progresses over time (usually a few weeks to months) to asymptomatic HIV infection (no symptoms) and then to early symptomatic (some symptoms) HIV infection. Later, it progresses to AIDS (very advanced HIV infection with T-cell count below 200).

Almost all people infected with HIV, if not treated, will develop AIDS. There is a small group of patients who develop AIDS very slowly, or never at all. These patients are called nonprogressors, and many seem to have a genetic difference that prevents the virus from damaging their immune system.

The symptoms of AIDS are primarily the result of infections that do not normally develop in individuals with healthy immune systems. These are called opportunistic infections.

People with AIDS have had their immune system depleted by HIV and are very susceptible to these opportunistic infections. Common symptoms are fevers, sweats (particularly at night), swollen glands, chills, weakness, and weight loss.

See the signs and tests section below for a list of common opportunistic infections and major symptoms associated with them.

Note: Initial infection with HIV can produce no symptoms. Some people, however, do experience flu-like symptoms with fever, rash, sore throat, and swollen lymph nodes, usually 2 weeks after contracting the virus. Some people with HIV infection remain without symptoms for years between the time the are exposed to the virus and when they develop AIDS.

The following is a list of AIDS-related infections and cancers that people with AIDS may get as their CD4 count decreases. In the past, having AIDS was defined as having HIV infection and getting one of these additional diseases. Today, according to the Centers for Disease Control and Prevention, a person is diagnosed as having AIDS if they have a CD4 cell count below 200, even if they don't have an opportunistic infection.

AIDS may also be diagnosed if a person develops one of the numerous infections and cancers that occur with HIV infection. These infections are unusual in people with a healthy immune system.

CD4 cells are a type of immune cell. They are also called "T cells" or "helper cells."

Many other illnesses and corresponding symptoms may develop in addition to those listed here.

Common with CD4 count below 350 cells/mcl:

• Herpes simplex virus -- causes ulcers/small blisters in the mouth or genitals, happens more frequently and usually much more severely in an HIV-infected person than before HIV infection
• Tuberculosis -- infection by the tuberculosis bacteria that mostly affects the lungs, but can affect other organs such as the bowel, lining of the heart or lungs, brain, or lining of the central nervous system (brain and spinal cord)
• Oral or vaginal thrush -- yeast infection of the mouth or vagina
• Herpes zoster (shingles) -- ulcers/small blisters over a patch of skin. it is caused by the varicella zoster virus
• Non-Hodgkin's lymphoma -- cancer of the lymph glands
• Kaposi's sarcoma -- cancer of the skin, lungs, and bowel, associated with a herpes virus (HHV-8). Can happen at any CD4 count, but is more likely to happen at lower CD4 counts, and is more common in men than in women

Common with CD4 count below 200 cells/mcl:

• Pneumocystis carinii pneumonia, "PCP pneumonia," now called Pneumocystic jiroveci pneumonia
• Candida esophagitis -- painful yeast infection of the esophagus
• Bacillary angiomatosis -- skin lesions caused by a bacteria called Bartonella, which is usually acquired from cat scratches

Common with CD4 count below 100 cells/mcl:

• Cryptococcal meningitis -- infection of the lining of the brain
• AIDS dementia -- worsening and slowing of mental function, caused by HIV itself
• Toxoplasmosis encephalitis -- infection of the brain by a parasite, called Toxoplasma, which is frequently found in cat feces; causes lesions (sores) in the brain
• Progressive multifocal leukoencephalopathy -- a viral disease of the brain caused by a virus (called the JC virus) that results in a severe decline in mental and physical functions
• Wasting syndrome -- extreme weight loss and loss of appetite, caused by HIV itself
• Cryptosporidium diarrhea -- Extreme diarrhea caused by one of several related parasites

Common with CD4 count below 50/mcl:

• Mycobacterium avium -- a blood infection by a bacterium related to tuberculosis
• Cytomegalovirus infection -- a viral infection that can affect almost any organ system, especially the large bowel and the eyes

In addition to the CD4 count, a test called HIV RNA load may be used to monitor patients. Basic screening lab tests and regular cervical Pap smears are important to monitor in HIV infection, due to the increased risk of cervical cancer in immunocompromised women. Anal Pap smears to detect potential cancers may also be important in both HIV infected men and women.

There is no cure for AIDS at this time. However, a variety of treatments are available that can help keep symptoms at bay and improve the quality of life of those who have already developed symptoms.

Antiretroviral therapy suppresses the replication of the HIV virus in the body. A combination of several antiretroviral agents, termed highly active antiretroviral therapy (HAART), has been highly effective in reducing the number of HIV particles in the blood stream, as measured by a blood test called the viral load. Preventing the virus from replicating can help the immune system recover from the HIV infection and improve T-cell counts.

HAART is not a cure for HIV, and people on HAART with suppressed levels of HIV can still transmit the virus to others through sex or sharing of needles. But HAART has been enormously effective for the past 10 years. There is good evidence that if the levels of HIV remain suppressed and the CD4 count remains high (above 200 cells/mcl), life can be significantly prolonged and improved.

However, HIV may become resistant to HAART in patients who do not take their medications on schedule every day. Genetic tests are now available to determine whether a particular HIV strain is resistant to a particular drug. This information may be useful in determining the best drug combination for each individual, and adjusting the drug regimen if it starts to fail. These tests should be performed any time a treatment strategy begins to fail, and prior to starting therapy.

When HIV becomes resistant to HAART, other drug combinations must be used to try to suppress the resistant strain of HIV. There are a variety of new drugs coming out on the market for the treatment of drug-resistant HIV.

Treatment with HAART has complications. HAART is a collection of different medications, each with its own side effects. Some common side effects are nausea, headache, weakness, malaise (a general sick feeling), and fat accumulation on the back ("buffalo hump") and abdomen. When used for a long time, these medications increase the risk of heart attack by increasing the levels of fat and glucose in the blood.

Any doctor prescribing HAART should carefully watch the patient for possible side effects associated with the combination of medications the patient takes. In addition, routine blood tests measuring CD4 counts and HIV viral load (a blood test that measures how much virus is in the blood) should be taken every 3 - 4 months. The goal is to get the CD4 count as close to normal as possible, and to suppress the HIV amount of virus in the blood to an undetectable level.

Other antiviral medications are being investigated. In addition, growth factors that stimulate cell growth, such as Epogen (erthythropoetin) and G-CSF are sometimes used to treat anemia and low white blood cell counts associated with AIDS.

Medications are also used to prevent opportunistic infections (such as Pneumocystis uiroveci pneumonia) if the CD4 count is low enough. This keeps AIDS patients healthier for longer periods of time. Opportunistic infections are treated when they happen.

Joining support groups where members share common experiences and problems can often help the emotional stress of devastating illnesses. See AIDS - support group.

Right now, there is no cure for AIDS. It is always fatal if no treatment is provided. In the US, most patients survive many years after diagnosis because of the availability of HAART. HAART has dramatically increased the amount of time people with HIV remain alive.

Research continues in the areas of drug treatments and vaccine development. Unfortunately, HIV medications are not always available in the developing world, where the bulk of the epidemic is raging.

When a person is infected with HIV, the virus slowly begins to destroy that person's immune system. How fast this occurs differs in each individual. Treatment with HAART can help slow and even halt the destruction of the immune system.

Once the immune system is severely damaged, that person has AIDS, and is now susceptible to infections and cancers that most healthy adults would not get. However, antiretroviral treatment can still be very effective, even at that stage of illness.

Call for an appointment with your health care provider if you have any of the risk factors for HIV infection, or if you develop symptoms of AIDS. By law, AIDS testing must be kept confidential. Your health care provider will review results of your testing with you.

1. See the article on safe sex to learn how to reduce the chance of acquiring or spreading HIV, and other sexually transmitted diseases.
2. Try not to use injected drugs. If IV drugs are used, do not share needles or syringes. Many communities now have needle exchange programs, where you can get rid of used syringes and get new, sterile ones for free. These programs can also provide referrals to addiction treatment.
3. Avoid contact with another person's blood. Protective clothing, masks, and goggles may be appropriate when caring for people who are injured.
4. Anyone who tests positive for HIV can pass the disease to others and should not donate blood, plasma, body organs, or sperm. An infected person should tell any prospective sexual partner about their HIV-positive status. They should not exchange body fluids during sexual activity, and should use whatever preventive measures (such as condoms) will give the partner the most protection.
5. HIV-positive women who wish to become pregnant should seek counseling about the risk to unborn children, and medical advances that may help prevent the fetus from becoming infected. Use of certain medications can dramatically reduce the chances that the baby will become infected during pregnancy.
6. Mothers who are HIV-positive should not breast feed their babies.
7. Safe-sex practices, such as latex condoms, are highly effective in preventing HIV transmission. HOWEVER, there remains a risk of acquiring the infection even with the use of condoms. Abstinence is the only sure way to prevent sexual transmission of HIV.

The riskiest sexual behavior is unprotected receptive anal intercourse -- the least risky sexual behavior is receiving oral sex. Performing oral sex on a man is associated with some risk of HIV transmission, but this is less risky than unprotected vaginal intercourse. Female-to-male transmission of the virus is much less likely than male-to-female transmission. Performing oral sex on a woman who does not have her period carries low risk of transmission.

HIV-positive patients who are taking anti-retroviral medications are less likely to transmit the virus. For example, pregnant women who are on effective treatment at the time of delivery, and who have undetectable viral loads, give HIV to the infant less than 1% of the time, compared with about 20% of the time if medications are not used.

The US blood supply is among the safest in the world. Nearly all people infected with HIV through blood transfusions received those transfusions before 1985, the year HIV testing began for all donated blood. Currently, the risk of infection with HIV through a blood transfusion or blood products is almost zero in the United States, even in geographic areas with a lot of HIV infections.

If you believe you have been exposed to HIV, seek medical attention IMMEDIATELY. There is some evidence that an immediate course of antiviral drugs can reduce the chances that you will be infected. This is called post-exposure prophylaxis (PEP), and has been used to treat health care workers injured by needlesticks, to prevent transmission.

There is less information available about how effective PEP is for people exposed to HIV through sexual activity or IV drug use. However, if you believe you have been exposed, you should discuss the possibility with a knowledgeable specialist (check local AIDS organizations for the latest information) as soon as possible. Anyone who has been raped should be offered PEP and should consider its potential risks and benefits.

Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: sect XXIV.