This document covers the most current scientific understandings of the factors that affect biological risk of HIV infection and transmission. There have been significant scientific advancements in understanding the biomedical aspects of HIV risk and prevention since the publication, HIV Transmission: Guidelines for Assessing Risk (Transmission Guidelines) was last updated in 2005.
This document primarily focuses on the risk of transmission through sexual contact. It summarizes the scientific evidence about the biomedical aspects of risk and transmission, without commenting on social or behavioural factors which are equally important but are beyond the scope of this document. Information about vertical transmission and risk due to drug use is covered in the Transmission Guidelines.