In addition to STIs, unprotected sex can have other health risks for HIV-positive people. There have been over 20 reported cases where a person with HIV has been reinfected, or superinfected with another subtype or strain of HIV which is resistant to anti-HIV drugs.

In some cases this has resulted in the person's HIV viral load increasing and CD4 cell count falling. In addition, their treatment options have been limited because the type of HIV they were reinfected with was resistant to some or all of the anti-HIV drugs they were taking as well as others they had never taken.

It is not known how easy it is for somebody to become reinfected with HIV. So far only a small number of cases have been reported worldwide, almost all amongst gay men who had unprotected anal sex. However, there has also been a case reported of reinfection involving a heterosexual couple.

Although reinfection appears to be rare, there seem to be some factors that might increase the risk of it happening. Many of the cases occurred soon after a person was first infected with HIV, and often when people were taking a break from anti-HIV treatment. There has also been a case of reinfection reported involving a man who had had HIV for many years. He already had resistance to most of the available anti-HIV drugs and had unprotected sex with lots of men.