Transmission of drug-resistant strains of HIV is well-documented. While studies from the late 1990s suggested that less than 10% of new infections d drug-resistant virus, recent studies suggest that many newly infected individuals are infected with an at least somewhat drug-resistant strain of HIV. As the uptake of antiretroviral therapy has spread, so has the transmission of drug-resistant virus.

(The overall prevalence of resistant virus, as opposed to transmitted resistant virus, is discussed above: see Limiting the chance of resistance).