- The most common route for HIV transmission is sexual contact, primarily through unprotected vaginal or anal intercourse.
- This mode accounts for the majority of new infections globally, as the virus is present in genital secretions and easily transmitted across mucosal surfaces.
- Transmission risk increases with factors such as coexisting sexually transmitted infections and high viral load.
- While blood transfusion and needle sharing are efficient transmission routes, they are less common due to screening and harm reduction programs.
- Vertical transmission is significant but less common compared to sexual transmission in the general population.

Reference: Davidson’s Principles and Practice of Medicine, 24th Edition, Chapter: HIV Infection and AIDS, Page 722.