Objective: To examine recent trends in transmitted drug resistance (TDR) in the United Kingdom.
Methods: Analysis of results of genotypic resistance tests reported to the UK HIV Drug Resistance Database, which includes virtually all tests conducted as part of routine clinical care nationally. Resistance was based on major mutations as defined in the 2005 International AIDS Society-USA guidelines. Analysis was restricted to persons who were antiretroviral treatment-naive at the time of sampling, and a test defined as relating to recent infection if the patient was co-enrolled in the UK Register of HIV Seroconverters and the sample taken within 18 months of a negative HIV antibody test.
Results: A total of 4454 samples from treatment-naive patients between 1996 and 2004 were analysed, including 316 from patients recently infected at the time of the resistance test. After an initial rise, TDR declined from a peak of around 14% in 2001-2002 to around 8% by the end of 2004 (Ptrend < 0.001), largely driven by a decrease in nucleos(t)ide reverse transcriptase inhibitor (NRTI) mutations. Non-NRTI resistance has become increasingly important in relative terms and is now as common as NRTI resistance. Among patients with recent infection, an almost identical pattern was observed but shifted approximately 2 years earlier. A change in the distribution of viral subtypes did not explain these temporal trends.
Conclusions: This is the first clear evidence of a decrease in TDR at national level. The wider use of regimens that suppress viral concentration to below infectious levels is one of several plausible explanations for this finding.