4% when minority assays for K103N, Y181C and M184V were included. This is a 45% (95% CI 15.2–83.7%; P=0.0020) increase in the detection of significant resistance-associated mutations using the more sensitive assays combined with standard genotyping, compared with standard genotyping alone. There was a temporal reduction Pexidartinib of TDR detected by standard methods from 15.4% in 2003 to 9.5% in 2006. This follows similar trends previously observed in UK TDR surveillance [3,5]. Taken together, the minority species methods showed a significant increase in detection over standard genotyping alone, with the M184V assay accounting for almost all of this increase. The 13-fold increase

in detection of M184V was significant (P=0.0005), while the 20% increase in detection of K103N did not reach statistical significance (P=0.5), and the Y181C mutation was not detected in this population by either method. The increased level of M184V detected by the more sensitive assay corresponds

with the observation that this is amongst the most common drug resistance mutations seen in treatment-experienced patients [6]; nevertheless, it is rarely seen in TDR studies using standard genotyping by population sequencing. The high fitness cost of the M184V mutation means that it may rapidly revert to wild-type (M184) levels that are undetectable with standard genotypic methods in the absence of drug pressure. Estimates suggest that M184V will revert to wild type within 6.5 months following seroconversion [14]. By contrast, primary nonnucleoside reverse transcriptase inhibitor (NNRTI) INCB024360 chemical structure mutations such as K103N have a low fitness cost [15]. Estimates of K103N reversion in treatment-naïve patients suggest that its presence is stable

in the plasma RNA for >3 years following seroconversion [16]. The findings we report here support the suggestion that M184V Nitroxoline is as likely to be transmitted as other mutations. Minority M184V/I populations were found in patients achieving successful response to first-line ART combinations containing emtricitabine [8]; consequently, the clinical significance of minority M184V is at present uncertain. Our observation that the M184V mutation occurred in only a minority of recent infections with other drug resistance mutations was surprising. This may indicate that the diagnostic use of minority assays to study only specimens with other resistance, as determined by standard genotypic methods, is inappropriate. The patient specimens were analysed using serological incidence testing to determine whether they came from a recent or long-standing infection. There was no significant difference between these two categories in terms of TDR rates. The issue of examining chronically HIV-infected patients to estimate rates of TDR is controversial because of high fitness cost mutations probably reverting to wild type over an extended period of time [17].