title: The impact of different definitions on the estimated rate of transmitted HIV drug resistance in the United Kingdom.
abstract: 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.
authors.affiliation: HIV Group, Medical Research Council Clinical Trials Unit, 222 Euston Road, London, United Kingdom. hannah.green@ctu.mrc.ac.uk
authors.forename: Hannah
authors.initials: H
authors.lastname: Green
authors.forename: Peter
authors.initials: P
authors.lastname: Tilston
authors.forename: Esther
authors.initials: E
authors.lastname: Fearnhill
authors.forename: Deenan
authors.initials: D
authors.lastname: Pillay
authors.forename: David T
authors.initials: DT
authors.lastname: Dunn