HIV/AIDS is spread through bodily fluids, most frequently blood, male seminal fluid, or female vaginal secretions. For transmission to occur, the infected fluid must enter the uninfected person's body through some kind of cut or opening in the skin or mucous membranes in the body.

The virus can be transmitted at any stage of infection. You need not be symptomatic, or even know you are infected, in order to pass the AIDS virus to someone else. People are most infectious within the first six months to one year following their own infection, and then six to ten years later as their immune system becomes more suppressed.