The two most common ways of HIV transmission in the United States are through sex and needle sharing, notes the Centers for Disease Control. Other less common transmission routes include through blood transfusions and from mother to child via placenta or through breast milk.
The human immunodeficiency virus is a retrovirus that first originated in African chimps, notes Mayo Clinic. The virus is transmitted through contact with sexual fluids, blood or breast milk. Sexual transmission is by far the most common method of getting infected with HIV, according to the CDC. Receptive anal sex has the highest rate of transmission, followed by insertive anal sex, vaginal sex and oral sex. Needle sharing, typically the sharing of contaminated needles with someone who is infected with HIV, is the second most common method of HIV infection.