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 in 2006, there were approximately 40 million people around the world 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 breast 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:
- Injection drug users who share needles
- Infants born to mothers with HIV who didn'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 screening for the virus became standard practice)
- Sexual partners of those who participate in high-risk activities (such as injuection drug use or 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 HIV infection. Later, it progresses to AIDS (advanced HIV infection with CD4 T-cell count below 200 cells/mm3 ).
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.