AIDS (Acquired Immune Deficiency Syndrome) is the final and most serious stage of HIV disease, which causes severe damage to the immune system.

The Centers for Disease Control has defined AIDS as beginning when a person with HIV infection has a CD4 cell (also called "t-cell", a type of immune cell) count below 200. It is also defined by numerous opportunistic infections and cancers that occur in the presence of HIV infection.

AIDS is the fifth leading cause of death among persons between ages 25 and 44 in the United States. About 47 million people worldwide have been infected with HIV since the start of the epidemic.

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

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

HIV has been found in saliva, tears, nervous system tissue, blood, semen (including pre-seminal fluid, or "pre-cum"), vaginal fluid, and breast milk. However, only blood, semen, vaginal secretions, and breast milk have been proven to transmit infection to others.

Transmission of the virus occurs:

1. through sexual contact -- including oral, vaginal, and anal sex
2. through blood -- via blood transfusions (now extremely rare in the U.S) or needle sharing
3. from mother to child -- a pregnant woman can passively transmit the virus to her fetus, or a nursing mother can transmit it to her baby

Other transmission methods are rare and include accidental needle injury, artificial insemination with donated semen, and through a donated organ.

HIV infection is not spread by casual contact (such as hugging and touching), by touching dishes, doorknobs, or toilet seats previously touched by a person infected with the virus, during participation in sports, or by mosquitoes.

It is not transmitted to a person who DONTATES blood or organs in the U.S. because hospitals do not re-use syringes and sterilize all devices involved in such procedures.

However, HIV can be transmitted to the person RECEIVING blood or organs from an infected donor. This is why blood banks and organ donor programs screen donors, blood, and tissues thoroughly.

Those at highest risk include homosexual or bisexual men engaging in unprotected sex, intravenous drug users who share needles, the sexual partners of those who participate in high-risk activities, infants born to mothers with HIV, and people who received blood transfusions or clotting products between 1977 and 1985 (prior to standard screening for the virus in the blood).

AIDS begins with HIV infection. People infected with HIV may have no symptoms for ten years or longer, but they can still transmit the infection to others during this symptom-free period. Meanwhile, their immune system gradually weakens until they develop AIDS.

Acute HIV infection progresses over time to asymptomatic HIV infection and then to early symptomatic HIV infection. Later, it progresses to AIDS (very advanced HIV infection with T-cell count below 200).

Most individuals infected with HIV will progress to AIDS, if not treated. However, there is a tiny group of patients who develop AIDS very slowly or never at all. These patients are called non-progressors and many seem to have a genetic difference which prevents the virus from attaching to certain immune receptors.

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."

Patients with AIDS have had their immune system depleted by HIV and are very susceptible to such 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 may produce no symptoms. Some people with HIV infection remain without symptoms for years between the time of exposure and development of AIDS. However, some people develop what feels like a "flu" about two weeks after contracting the virus.

The following is a list of AIDS-related infections and cancers that people with AIDS acquire as their CD4 count decreases. Previously, having AIDS was defined by having HIV infection and acquiring one of these additional diseases, but now it is simply defined as a CD4 count below 200. Many other illnesses and corresponding symptoms may develop in addition to those listed here.

Common with CD4 count below 350/ml:

• Herpes Simplex Virus -- causes ulcers in your mouth or genitals, occurring more frequently and more severely than previously
• Tuberculosis -- infection by the tuberculosis bacteria that predominately affects the lungs
• Oral or vaginal thrush -- yeast infection of the mouth or genitals
• Herpes zoster -- ulcers over a discrete patch of skin caused by this virus
• Non-Hodgkins Lymphoma -- cancer of the lymph glands

CD4 count below 200/ml

• Pneumocystis carinii pneumonia, "PCP pneumonia"
• Candida esophagitis -- painful yeast infection of the esophagus

CD4 count below 100/ml

• Cryptococcal meningitis -- infection of the brain by this fungus
• AIDS Dementia -- worsening and slowing of mental function caused by HIV itself
• Toxoplasmosis encephalitis -- infection of the brain by this parasite, which is frequently found in cat feces
• Progressive multifocal leukoencephalopathy -- a viral disease of the brain caused by a virus (called the JC virus) that results in a quick decline in cognitive and motor functions
• Wasting Syndrome -- extreme weight loss and anorexia caused by HIV

CD4 count below 50/ml

• 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 eyes

In addition to the CD4 lymphocyte count, chest X-rays, Pap smears, and other tests are useful in managing HIV disease. Gay men who engage in receptive anal sex may wish to consider anal Pap smears to detect potential cancers.

There is no cure for AIDS at this time. However, several treatments are available that can delay the progression of disease for many years and improve the quality of life of those who have developed symptoms.

Antiviral therapy suppresses the replication of the HIV virus in the body. A combination of several antiretroviral agents, termed Highly Active Anti-Retroviral 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). This can help the immune system bounce back for a while and improve T-cell counts.

Although this 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, the treatment shows great promise.

There is good evidence that if the levels of HIV remain suppressed and the CD4 count remains high (>200), that life and quality of life can be significantly prolonged and improved. However, HIV tends to become resistant in patients who do not take their medications every day. Also, certain strains of HIV mutate easily and may become resistant to HAART especially quickly.

Genetic tests are now available to determine whether the virus is resistant to a particular drug -- these may be useful in determining the best drug combination and adjusting it if it starts to fail.

When HIV becomes resistant to HAART, salvage therapy is required to try to suppress the resistant strain of HIV. Different combinations of medications are tried to attempt to reduce viral load. This is often not successful, unfortunately, and the patient will usually develop AIDS and its complications.

Treatment with HAART is not without complications. HAART is a collection of different medications, each with its own side effect profile. Some common side effects are nausea, headache, weakness, malaise, and fat accumulation on your back and abdomen ("buffalo hump," lipodystrophy). When used long-term, these medications may increase the risk of heart attack by affecting fat metabolism.

Any doctor prescribing HAART should be carefully following the patient for possible side effects associated with the combination of medications being taken. 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 three to four months. The goal is to get the CD4 count as close to normal as possible, and to suppress the HIV viral load to an undetectable level.

Other antiviral agents are in investigational stages and many new drugs are in the pipeline. 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 carinii pneumonia) and can keep AIDS patients healthier for longer periods of time. Opportunistic infections are treated as they occur.

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

At the present time, there is no cure for AIDS. It has proven to be a universally fatal illness. However, most patients survive many years following diagnosis. HAART has dramatically increased the time from diagnosis to death, and research continues in drug treatments and vaccine development.

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

However, once the immune system is severely destroyed, that patient is said to have developed AIDS, and is now susceptible to infections and cancers that most healthy adults would not get.

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

Prevention of AIDS requires foresight and self-discipline. The requirements often seem personally restrictive, but they are effective and can save your life.

1. Do not have sexual intercourse with:

• People known or suspected to be infected with AIDS
• Multiple partners
• A person who has multiple partners
• People who use IV drugs

2. Do not use intravenous drugs. If IV drugs are used, do not share needles or syringes. Many communities now have needle exchange programs where used syringes can be disposed of and new, sterile needles obtained for free. These programs can also provide referrals to addiction treatment.

3. Avoid exposure to blood from injuries or nosebleeds where the HIV status of the bleeding individual is unknown. Protective clothing, masks, and goggles may be appropriate when caring for people who are injured.

4. Anyone who tests positive for HIV may pass the disease on to others and should not donate blood, plasma, body organs, or sperm. From a legal, ethical, and moral standpoint, they should warn any prospective sexual partner of their HIV positive status. They should not exchange body fluids during sexual activity and must use whatever preventative measures (such as a latex condom) will afford the partner the most protection.

5. HIV positive women should be counseled before becoming pregnant about the risk to unborn children and medical advances which 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.

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.

8. Other information on sexual risk reduction: 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.

9. HIV-positive patients who are taking anti-retroviral medications are less likely to transmit the virus. For example, pregnant women who are on treatment at the time of delivery transmit HIV to the infant about 5% of the time, compared to approximately 20% if medications are not used.

10. The U.S. 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 in the United States through receiving a blood transfusion or blood products is extremely low and has become progressively lower, even in geographic areas with high HIV prevalence.

11. If you believe you have been exposed to HIV, seek medical attention IMMEDIATELY. There is some evidence that an immediate course of anti-viral drugs can reduce the chances that you will be infected. This is called post-exposure prophylaxis (PEP), and it has been used to treat health care workers injured by needlesticks for years. There is less information on the effectiveness of PEP for people exposed via sexual activity or intravenous 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. All rape victims should be offered PEP and should consider its potential risks and benefits in their particular case.