HIV stands for human immunodeficiency virus. This is the virus that causes AIDS. HIV is different from most other viruses because it attacks the immune system. The immune system gives our bodies the ability to fight infections. HIV finds and destroys a type of white blood cell (T cells or CD4 cells) that the immune system must have to fight disease.

For more information view our questions and answers on HIV science.

AIDS

Origin of HIV

Scientists identified a type of chimpanzee in West Africa as the source of HIV infection in humans. The virus most likely jumped to humans when humans hunted these chimpanzees for meat and came into contact with their infected blood. Over several years, the virus slowly spread across Africa and later into other parts of the world.

Brief History of HIV in the United States

HIV was first identified in the United States in 1981 after a number of gay men started getting sick with a rare type of cancer. It took several years for scientists to develop a test for the virus, to understand how HIV was transmitted between humans, and to determine what people could do to protect themselves.

In 2008, CDC adjusted its estimate of new HIV infections because of new technology developed by the agency. Before this time, CDC estimated there were roughly 40,000 new HIV infections each year in the United States. New results shows there were dramatic declines in the number of new HIV infections from a peak of about 130,000 in the mid 1980s to a low of roughly 50,000 in the early 1990s. Results also shows that new infections increased in the late 1990s, followed by a leveling off since 2000 at about 55,000 per year. In 2006, an estimated 56,300 individuals were infected with HIV.

AIDS cases began to fall dramatically in 1996, when new drugs became available. Today, more people than ever before are living with HIV/AIDS. CDC estimates that about 1 million people in the United States are living with HIV or AIDS. About one quarter of these people do not know that they are infected: not knowing puts them and others at risk.

How HIV Is and Is Not Transmitted

HIV is a fragile virus. It cannot live for very long outside the body. As a result, the virus is not transmitted through day-to-day activities such as shaking hands, hugging, or a casual kiss. You cannot become infected from a toilet seat, drinking fountain, doorknob, dishes, drinking glasses, food, or pets. You also cannot get HIV from mosquitoes.

• Having sex (anal, vaginal, or oral) with someone infected with HIV
• Sharing needles and syringes with someone infected with HIV
• Being exposed (fetus or infant) to HIV before or during birth or through breast feeding

HIV also can be transmitted through blood infected with HIV. However, since 1985, all donated blood in the United States has been tested for HIV. Therefore, the risk for HIV infection through the transfusion of blood or blood products is extremely low. The U.S. blood supply is considered among the safest in the world.

Risk Factors for HIV Transmission

• injected drugs or steroids, during which equipment (such as needles, syringes, cotton, water) and blood were shared with others

• had unprotected vaginal, anal, or oral sex (that is, sex without using condoms) with men who have sex with men, multiple partners, or anonymous partners

• exchanged sex for drugs or money

• been given a diagnosis of, or been treated for, hepatitis, tuberculosis (TB), or a sexually transmitted disease (STD) such as syphilis
• received a blood transfusion or clotting factor during 1978–1985

• had unprotected sex with someone who has any of the risk factors listed above

Preventing Transmission

Your risk of getting HIV or passing it to someone else depends on several things. Do you know what they are? You might want to talk to someone who knows about HIV. You can also do the following:

• Abstain from sex (do not have oral, anal, or vaginal sex) until you are in a relationship with only one person, are having sex with only each other, and each of you knows the other’s HIV status.
  • If both you and your partner have HIV, use condoms to prevent other sexually transmitted diseases (STDs) and possible infection with a different strain of HIV.
  • If only one of you has HIV, use a latex condom and lubricant every time you have sex.
• If you have, or plan to have, more than one sex partner, consider the following:
  • Get tested for HIV
    • If you are a man who has had sex with other men, get tested at least once a year.
    • If you are a woman who is planning to get pregnant or who is pregnant, get tested as soon as possible, before you have your baby.
  • Talk about HIV and other STDs with each partner before you have sex.
  • Learn as much as you can about each partner’s past behavior (sex and drug use), and consider the risks to your health before you have sex.
  • Ask your partners if they have recently been tested for HIV; encourage those who have not been tested to do so.
  • Use a latex condom and lubricant every time you have sex.
  • If you think you may have been exposed to another STD such as gonorrhea, syphilis, or Chlamydia trachomatis infection, get treatment. These diseases can increase your risk of getting HIV.
  • Get vaccinated against hepatitis B virus.
• Even if you think you have low risk for HIV infection, get tested whenever you have a regular medical check-up.
• Do not inject illicit drugs (drugs not prescribed by your doctor). You can get HIV through needles, syringes, and other works if they are contaminated with the blood of someone who has HIV. Drugs also cloud your mind, which may result in riskier sex.
• If you do inject drugs, do the following:
  • Use only clean needles, syringes, and other works.
  • Never share needles, syringes, or other works.
  • Be careful not to expose yourself to another person's blood.
  • Get tested for HIV test at least once a year.
  • Consider getting counseling and treatment for your drug use.
  • Get vaccinated against hepatitis A and B viruses.
• Do not have sex when you are taking drugs or drinking alcohol because being high can make you more likely to take risks.

To protect yourself, remember these ABCs:

A=Abstinence

B=Be Faithful

C=Condoms

Symptoms of HIV Infection

HIV Testing

Finding a Testing Site

You can locate a testing site by visiting the CDC HIV testing database or by calling CDC-INFO (formerly the CDC National AIDS Hotline) at 1-800-CDC-INFO (1-800-232-4636) 24 Hours/Day. You do not have to give any personal information about yourself to use these services to find a testing site.

Additional Resources for Basic Information

• CDC Questions and Answers on HIV/AIDS
• CDC Fact Sheet: HIV and Its Transmission
• CDC Fact Sheet: HIV Type 2
• MedLine AIDS Tutorial (NLM)
• HIV Infection and AIDS: An Overview (NIH)
• The Evidence That HIV Causes AIDS (NIH)
• How HIV Causes AIDS (NIH)
• The Origin of HIV (NIH)
• Glossary of HIV/AIDS-Related Terms (AIDSInfo)