Transmission of Human Immunodeficiency Virus

Approximately 99 percent of HIV infections result from unprotected sex with someone who is infected, sharing needles or syringes with someone who is infected, or being born to a woman who is infected and is not taking antiretroviral drugs.

Women who are HIV positive and are pregnant or considering having a child should talk to their physician or other health care provider about the importance of antiretroviral therapy to reduce the risk for transmitting the virus to their baby. For more information about preventing transmission and the risks associated with various sexual behaviors, see Prevention: Safer Sex.

HIV is transmitted in the following ways:
  • Sexual contact with an infected partner, including vaginal, anal, or oral intercourse (HIV can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth.)
  • Sharing needles or syringes contaminated with infected blood (including needles used for shooting drugs, piercing, or tattooing)
  • From infected women to the fetus during pregnancy or birth (Approximately 25–33 percent of women who are untreated pass the infection to their babies. Antiretroviral therapy reduces this risk.)
  • Through breast milk of infected mothers
  • Contact between a mucous membrane (e.g., lining of the vagina, vulva, penis, rectum, mouth) and infected blood

Based on available evidence, HIV is not transmitted through the following:

  • Saliva
  • Sweat, tears, urine or feces
  • Biting insects, such as mosquitoes
  • Casual contact, such as:
    • sitting next to someone;
    • touching, hugging, or shaking hands;
    • eating in the same restaurant or cafeteria;
    • swimming in the same pool or using the same shower or tub; or
    • using the same toilet seat
  • Blood transfusions (Blood donors are now carefully screened and blood is tested before being used.)

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 30 Nov 2000

Last Modified: 12 Aug 2015