A major area of research activity by the database is the national surveillance of HIV-1 drug resistance, tracking changes in its prevalence over time. Analyses are done separately for drug-naïve patients to monitor transmitted drug resistance (TDR), and drug-experienced patients to monitor the extent of resistance by drug class and prevalence of multi-class resistance.
Rates of HIV drug resistance are shown in the tables and graphs below.
TDR is an important phenomenon that can limit therapeutic options for newly-infected patients. In the UK, TDR to any drug class decreased from around 13% to 7% between 2002 and 2006. This is mainly attributed to changes in testing guidelines and the increasing proportion of patients on therapy who are virologically suppressed. From 2006-2008, TDR increased slightly from 7% to 8%,and then remained stable until 2010. In recent years, from 2011-2014 we have seen rates of TDR decrease slightly to 7.3% in 2014. This decrease is likely to be the result of increasing use of better combination treatments for HIV leading to more patients being virologically supressed and therefore not transmitting resistant strains. NRTI resistance has decreased most sharply from 2002-2014 as a result of diminishing use of old NRTI drugs that selected for thymidine analogue mutations. Rates of NNRTI and PI resistance have remained more stable. Very little of the TDR seen in recent years, 2010-2014, is clinically relevant for patients starting therapy on the currently recommended first line treatments.
Drug experienced patients
Analyses of drug-experienced patients (who, by definition, have experienced virological failure) provide insights into the extent of resistance within and across drug classes and estimates of the number of individuals with multi-class resistance. Among drug-experienced patients, the prevalence of resistance to any drug class fell markedly from 72.4% in 2002 to 30% in 2014. This is probably due to the increasingly lower clinical threshold for resistance testing and the improved potency of antiretrovirals. NRTI resistance closely mirrored the overall trend and now has a prevalence lower than NNRTI resistance. Levels of NNRTI resistance decreased to around 20% in 2014 and PI resistance fell to 2.4% in 2014.
A more detailed discussion of some of these findings can be found in several surveillance-related publications, including in annual reports from Public Health England. Please see the Publications and presentations page.
Prevalence of HIV drug resistance (%) in ART-naïve patients by calendar year (TDR defined as ≥1 mutation from WHO 2009 surveillance list)
Prevalence of HIV drug resistance (%) in ART-experienced patients by calendar year (Resistance defined as ≥1 major mutation from IAS 2014 list)