Our current definition could lead to an over-estimation of the prevalence of tropism switch if results were to apply to the current definition of undetectable viremia which is typically 20�C50 copies/mL. Indeed, our secondary Rituximab analysis showed that when suppression was redefined to,50 copies/mL, we detected a lower prevalence of R5-to-non-R5 switches. A second study limitation was our choice of pre-HAART tropism as the comparator. Although the length of time between HAART initiation and viral suppression was not significantly associated with tropism switch, some patients in this study achieved viral suppression over one year after therapy initiation, allowing active viral replication and potential viral evolution. Indeed, when we tested additional samples collected immediately before or after viral load suppression from these individuals, we observed 35% of the patients who experienced R5-to-non-R5 switches could be explained by switches during the initial decline in viremia prior to suppression or by post-suppression switches. A third study limitation was ES936 genotypic tropism determination methods�� limited sensitivity/specificity relative to the ����true���� viral tropism or to the clinical outcomes of individuals receiving CCR5- antagonist-based regimens. It is important to understand that even ESTA, a phenotypic tropism determination assay, is limited by sensitivity and specificity. While a 100% sensitive method to determine viral tropism does not exist because there is no distinct gold standard for HIV viral tropism, populationsequencing- based genotypic tropism prediction has been reported to predict maraviroc-based regimen virological outcome and have a sensitivity of 67.4% and specificity of 92.6% against a phenotypic assay, which implies that our reported prevalence of post-HAART tropism change can only be taken as an estimation. Overall, this study showed that R5-to-non-R5 tropism switches after periods of suppressive-HAART were relatively rare events, especially in patients with higher CD4 counts during suppression and/or patients with a lower prevalence of circulating non-R5 quasispecies in their baseline plasma samples.