Background:  The transmission of drug-resistant HIV to a new host results in dissemination and persistent infection by a monoclonal or oligo-clonal population of resistant virus. Initial ART has been shown to fail more frequently in persons infected with a drug resistant strain. The prevalence of transmitted drug resistance in recently infected and chronically infected patients will be reviewed. Transmitted drug resistant variants have been shown to persist for years in ART-naïve subjects. The natural history will be reviewed for 14 individuals who were infected with drug-resistant HIV after sexual exposure and who were followed after with primary infection for as long as 4.3 years, while electing to defer ART. These data demonstrate that sexual transmission appears to select for more fit resistant variants that emerge during treatment of chronic infection (ie, acquired resistance) and these highly replication-competent, drug-resistant variants usually persist for years at high levels. In addition, transmitted drug-resistant virus persists as long, if not longer, in the genital tract compartment than the plasma compartment, raising concerns about further transmission of drug resistant virus. 

Conclusions:  The prevalence of transmitted drug resistance in most surveillance studies and the long-term persistence of this drug resistance strongly support the routine use of HIV resistance genotyping for all newly HIV diagnosed subjects.