doi:10.1155/2012/230290 Research Article

Copyright © 2012 Kate Buchacz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Little is known about temporal trends in frequencies of clinically relevant ARV resistance mutations in HIV strains from U.S. patients undergoing genotypic testing (GT) in routine HIV care. Methods. We analyzed cumulative frequency of HIV resistance among patients in the HIV Outpatient Study (HOPS) who, during 1999–2008 and while prescribed antiretrovirals, underwent GT with plasma HIV RNA>1,000 copies/mL. Exposure ≥4 months to each of three major antiretroviral classes (NRTI, NNRTI and PI) was defined as triple-class exposure (TCE). Results. 906 patients contributed 1,570 GT results. The annual frequency of any major resistance mutations decreased during 1999–2008 (88 % to 79%, P = 0.05). Resistance to PIs decreased among PI-exposed patients (71 % to 46%, P = 0.010) as exposure to ritonavir-boosted PIs increased (6 % to 81%, P < 0.001). Non-significant declines were observed in resistance to NRTIs among NRTI-exposed (82 % to 67%), and triple-class-resistance amon