How is HIV passed from one person to another?

Only certain fluids--blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk--from an HIV-infected person can transmit HIV. These fluids must come in contact with a mucous membrane or damaged tissue or be directly injected into the bloodstream (from a needle or syringe) for transmission to possibly occur. Mucous membranes can be found inside the rectum, the vagina, the opening of the penis, and the mouth.
In the United States, HIV is spread mainly by
  • Having sex with someone who has HIV. In general:
    • Anal sex is the highest-risk sexual behavior.
    • Vaginal sex is the second highest-risk sexual behavior.
    • Having multiple sex partners or having other sexually transmitted infections can increase the risk of infection through sex.
  • Sharing needles, syringes, rinse water, cotton, cookers or other equipment used to prepare injection drugs with someone who has HIV.

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