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Virologic rebound early in treatment is frequently associated with genotypic resistance, but the source of resistant viruses has not been fully elucidated. One possibility is that preexisting low-frequency resistance mutations emerge during treatment failure. To evaluate this possibility, investigators studied 4 patients who experienced early virologic failure on an initial treatment regimen (tenofovir, 3TC, and an NNRTI — either efavirenz or nevirapine) and 18 control patients who received comparable treatment but did not experience virologic failure.
None of the patients had demonstrable resistance mutations on population-based genotypic sequencing conducted before treatment initiation. However, use of an allele-specific real-time PCR assa…