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How HIV is spread

a second view of HIV under a microscope

HIV under a microscope
Photo credit: Centers for Disease Control and Prevention

How HIV is spread

HIV is spread through some of the body's fluids. HIV is in:

  • Blood
  • Semen
  • Vaginal fluids
  • Breast milk
  • Some body fluids that may be handled by health care workers (fluids surrounding the brain and spinal cord, bone joints, and around an unborn baby)

HIV may be passed from one person to another by:

  • More common
    • Having sex (vaginal, anal, or oral) with a person who has HIV
    • Sharing needles with someone who has HIV, such as when using drugs
    • Pregnancy, labor, birth, or breastfeeding if a mother has HIV
  • Less common
    • Blood transfusion from an HIV positive blood donor, which is very unlikely today because U.S. blood banks test donated blood for HIV
    • Eating food that has been pre-chewed by an HIV-infected person. The blood in a caregiver's mouth can mix with food while chewing. This is rare and has only been noted among infants whose HIV positive caregiver gave them pre-chewed food.
    • Using a dirty tattooing needle (if it was used before on someone with HIV). Make sure the needle is new.
    • Sharing a toothbrush or razor with someone who has HIV

HIV is not spread through:

  • Kissing (there is a small chance of getting HIV from open-mouthed or "French" kissing if there's contact with blood)
  • Touching, hugging, or handshakes
  • Sharing food or drinks
  • Sharing food utensils, towels and bedding, telephones, or toilet seats
  • Donating blood
  • Working with or being around someone with HIV
  • Biting insects, such as mosquitoes
  • Swimming pools or drinking fountains
  • Playing sports

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The science behind HIV

HIV attacks and destroys the immune system's infection-fighting cells, called CD4 cells. They also are called CD4 positive T cells. HIV gets into these cells, makes copies of itself, and kills the healthy cells. As a person loses CD4 cells, the immune system weakens, making it harder for the body to fight infections and cancer. There are many different strains (types) of HIV. Most people have the HIV-1 strain. But, a person can be infected with more than one strain at a time.

HIV turns to AIDS when the immune system gets very weak. One way to know if a person has AIDS is if her CD4 cell count (the number of CD4 cells in a sample of blood) is very low (less than 200). Another way is if she has certain infections or cancers. Moving from HIV to AIDS is different for everyone. Some people live for 10 years or more with HIV without developing AIDS. Others get AIDS faster.

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Content last updated: July 01, 2011.

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