Background: The use of different lists of resistance mutations has resulted in estimates of transmitted HIV drug resistance (THDR) that are often not comparable.
Methods: We estimated the rate of THDR based on the 3 definitions: > or =1 major mutation(s) listed on the International AIDS Society (IAS)-USA drug resistance mutation (DRM) 2006 list; > or =1 surveillance drug resistance mutation(s) (SDRM) on the published list by Shafer et al; and low-level/intermediate/high-level resistance to > or =1 drug(s) according to the Stanford HIVdb interpretation algorithm. Analyses were based on genotypic resistance tests conducted during 1997-2005 on antiretroviral therapy-naive patients and reported to the UK HIV Drug Resistance Database. The effect on THDR rates of revisions to the IAS-DRM list was also examined.
Results: Overall, 10.0%, 9.2%, and 10.4% of the 8272 samples available for analysis were classified as having THDR by the IAS-DRM, SDRM, and Stanford definitions, respectively; however, there was discordance for 244 (3%) samples. Changes in the version of the IAS-DRM list over time resulted in 4%-7% differences in the estimated rate of THDR, which increased from 4%-5% during 1997-2000 to 5%-7% during 2001-2005.
Conclusions: The choice of genotypic definition had a minor influence on the estimated rate of THDR. The SDRM list is recommended for epidemiological estimates of THDR as it has been designed with such studies in mind.