HIV is not spread through the air, in food, or by casual social contact such as shaking hands or hugging. The virus is passed on only when blood or sexual secretions, such as semen, enter another person's body. HIV can also be spread to babies by the breast milk of an infected mother. Spread of the virus can occur during such activities as:

• unprotected sexual activity
• sharing IV needles
• being born to or breast-fed by an HIV-infected mother
• blood transfusions (now rare in the US because of current screening tests).

The following groups have the highest risk for HIV infection and the development of AIDS:

• sexually active homosexual men
• bisexual men and their partners
• IV drug users and their sexual partners
• people who share needles (for IV drug use, tattooing, or piercing)
• heterosexual men and women with more than one sexual partner
• people given transfusions of blood or blood products in countries where the blood is not rigorously tested
• immigrants from areas with many cases of AIDS (such as Haiti and east central Africa)
• people who have sex with an HIV-infected partner or with anyone in the above groups if they do not always use a latex or polyurethane condom
• babies born to HIV-infected mothers.