Sexual transmission: The contact between sexual secretions of the infected person with the rectal, genital or oral mucous membranes of another.

Exposure to blood-borne pathogens: Sharing and reusing syringes contaminated with HIV infected blood has a major risk for acquiring infection with HIV.

Perinatal transmission: The transmission of the virus from the mother to the child can occur in utero during the last weeks of pregnancy and at childbirth.