HIV lives in an infected person's blood and sexual fluid (semen or vaginal fluid). Nursing mothers who are infected also have some HIV in their breast milk. HIV spreads between people via these body fluids.
There are several common ways that HIV can be passed from person to person, including:
- Having unprotected sex with someone who is infected. Worldwide 80% of new HIV infections occur through vaginal sex and another large proportion of infections are transmitted through anal sex. Women are particularly at risk of infection through sex.
- Transmission from mother to child. Without anti-HIV treatment, an infected mother may pass the virus to her child during pregnancy, birth, or breastfeeding. Although mother-to-child transmission is preventable and transmission is rare in the United States, almost 400,000 infants are infected each year through their mothers globally; most of these infections occur in sub-Saharan Africa.
- Using needles or syringes that have been used by people who are infected.
- Receiving infected blood products or transplanted organs. Since 1985, the United States tests all donated blood for HIV; therefore, the risk of getting HIV in this way in the United States is now extremely low, and the risk is also decreasing in other countries as they improve their blood testing methods.
Some people are at higher risk of getting HIV.