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HIV Transmission

March 25, 2010

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How is HIV passed from one person to another?

HIV can be detected in several fluids and tissue of a person living with HIV. It is important to understand however, that finding a small amount of HIV in a body fluid or tissue does not mean that HIV is transmitted by that body fluid or tissue. Only specific fluids (blood, semen, vaginal secretions, and breast milk) from an HIV-infected person can transmit HIV. These specific fluids must come in contact with a mucous membrane or damaged tissue or be directly injected into the blood-stream (from a needle or syringe) for transmission to possibly occur.

In the United States, HIV is most commonly transmitted through specific sexual behaviors (anal or vaginal sex) or sharing needles with an infected person. It is less common for HIV to be transmitted through oral sex or for an HIV-infected woman to pass the virus to her baby before or during childbirth or after birth through breastfeeding or by prechewing food for her infant. In the United States, it is also possible to acquire HIV through exposure to infected blood, transfusions of infected blood, blood products, or organ transplantation, though this risk is extremely remote due to rigorous testing of the U.S. blood supply and donated organs.

For more information, see How safe is the blood supply in the United States?

Some healthcare workers have become infected after being stuck with needles containing HIV-infected blood or, less frequently, when infected blood comes in contact with a worker's open cut or is splashed into a worker's eyes or inside their nose. There has been only one instance of patients being infected by an HIV-infected dentist.

For more information, see "Are health care workers at risk of getting HIV on the job?" and "Are patients in a health care setting at risk of getting HIV?" If you would like more information or have personal concerns, call CDC-INFO 24 Hours/Day at 1-800-CDC-INFO (232-4636), 1-888-232-6348 (TTY), in English, en Español.

Which body fluids transmit HIV?

These body fluids have been shown to contain high concentrations of HIV:

  • blood
  • semen
  • vaginal fluid
  • breast milk
  • other body fluids containing blood

The following are additional body fluids that may transmit the virus that health care workers may come into contact with:

  • fluid surrounding the brain and the spinal cord
  • fluid surrounding bone joints
  • fluid surrounding an unborn baby

How well does HIV survive outside the body?

Scientists and medical authorities agree that HIV does not survive well outside the body, making the possibility of environmental transmission remote. HIV is found in varying concentrations or amounts in blood, semen, vaginal fluid, breast milk, saliva, and tears. To obtain data on the survival of HIV, laboratory studies have required the use of artificially high concentrations of laboratory-grown virus. Although these unnatural concentrations of HIV can be kept alive for days or even weeks under precisely controlled and limited laboratory conditions, CDC studies have shown that drying of even these high concentrations of HIV reduces the amount of infectious virus by 90 to 99 percent within several hours. Since the HIV concentrations used in laboratory studies are much higher than those actually found in blood or other specimens, drying of HIV-infected human blood or other body fluids reduces the theoretical risk of environmental transmission to that which has been observed?essentially zero. Incorrect interpretations of conclusions drawn from laboratory studies have in some instances caused unnecessary alarm.

Results from laboratory studies should not be used to assess specific personal risk of infection because (1) the amount of virus studied is not found in human specimens or elsewhere in nature, and (2) no one has been identified as infected with HIV due to contact with an environmental surface. Additionally, HIV is unable to reproduce outside its living host (unlike many bacteria or fungi, which may do so under suitable conditions), except under laboratory conditions; therefore, it does not spread or maintain infectiousness outside its host.

Can I get HIV from anal sex?

Yes. In fact, unprotected (without a condom) anal sex (intercourse) is considered to be very risky behavior. It is possible for either sex partner to become infected with HIV during anal sex. HIV can be found in the blood, semen, pre-seminal fluid, or vaginal fluid of a person infected with the virus. In general, the person receiving the semen is at greater risk of getting HIV because the lining of the rectum is thin and may allow the virus to enter the body during anal sex. However, a person who inserts his penis into an infected partner also is at risk because HIV can enter through the urethra (the opening at the tip of the penis) or through small cuts, abrasions, or open sores on the penis.

Not having (abstaining from) sex is the most effective way to avoid HIV. If people choose to have anal sex, they should use a latex condom. Most of the time, condoms work well. However, condoms are more likely to break during anal sex than during vaginal sex. Thus, even with a condom, anal sex can be risky. A person should use generous amounts of water-based lubricant in addition to the condom to reduce the chances of the condom breaking.

For more information on latex condoms, see "Male Latex Condoms and Sexually Transmitted Diseases."

If you would like more information or have personal concerns, call CDC-INFO 24 Hours/Day at 1-800-CDC-INFO (232-4636), 1-888-232-6348 (TTY), in English, en Español.

Can I get HIV from vaginal sex?

Yes, it is possible for either partner to become infected with HIV through vaginal sex* (intercourse). In fact, it is the most common way the virus is transmitted in much of the world. HIV can be found in the blood, semen (cum), pre-seminal fluid (pre-cum) or vaginal fluid of a person infected with the virus.

In women, the lining of the vagina can sometimes tear and possibly allow HIV to enter the body. HIV can also be directly absorbed through the mucous membranes that line the vagina and cervix.

In men, HIV can enter the body through the urethra (the opening at the tip of the penis) or through small cuts or open sores on the penis.

Risk for HIV infection increases if you or a partner has a sexually transmitted disease (STD). See also "Is there a connection between HIV and other sexually transmitted diseases?"

Not having (abstaining from) sex is the most effective way to avoid HIV. If you choose to have vaginal sex, use a latex condom to help protect both you and your partner from HIV and other STDs. Studies have shown that latex condoms are very effective, though not perfect, in preventing HIV transmission when used correctly and consistently. If either partner is allergic to latex, plastic (polyurethane) condoms for either the male or female can be used.

For more information on latex condoms, see "Male Latex Condoms and Sexually Transmitted Diseases."

If you have additional questions or are concerned about personal behaviors, call CDC-INFO 24 Hours/Day at 1-800-CDC-INFO (232-4636), 1-888-232-6348 (TTY), in English, en Español.

* For the purpose of this FAQ, vaginal sex or intercourse refers to sexual activity between a man and a woman involving the insertion of the penis into the vagina.

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This article was provided by U.S. Centers for Disease Control and Prevention. Visit the CDC's website to find out more about their activities, publications and services.
 
See Also
Quiz: Are You at Risk for HIV?
Ten Common Fears About HIV Transmission
Visit Our "Ask the Experts" Forum on HIV Risk and Transmission
More Frequently Asked Questions About HIV and AIDS

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