Actually, the transmission of AIDS requires two conditions to be met simultaneously: first, a sufficient number of active HIV viruses are needed. Second, these sufficient and active HIV viruses must enter fresh blood or a fresh wound.

Only when both of these conditions are met, is there a possibility of infection, but it is not a 100% certainty. For example, in the case of needle stick injuries involving needles contaminated with HIV-positive blood, the risk of infecting healthcare workers is about 0.3%.