Exactly how much this happens is unknown, but certainly some number of infections occur this way. However, the reality also is that such acts are seldom deliberate. If they lack essential knowledge about how transmission occurs, HIV-postive persons might not understand the risk their behavior poses, even though they know they are infected. HIV-postive individuals may be in a form of denial about their infection.
Infections happen as a result of sex or drug use, both very powerful drivers.
Rejection upon acknowledging HIV-postive status is the norm, establishing a negative incentive for voluntary disclosure. Complacency results from the improved treatments available today. This is one of the most common rationales among gay men. And because of such human frailty, it is essential that we each exercise responsibility for our own decision making, too. The Potential Criminality of HIV Transmission.