The genotypic results were interpreted using three commonly used rule-base interpretation systems: Agence Nationale de recherches sur le SIDA (ANRS) version 17; Stanford HIVdb, version 5.1.2; and Rega Institute version 8.0.1. The ANRS and Rega both report 3 levels of resistance: susceptible, intermediate, and resistant. For ANRS, we translated the definitions ‘susceptible’, ‘intermediate’, and ‘resistant’ into susceptibility scores of 1, 0.5, and 0, respectively. For the Rega scores, we used the weighted score suggested by Rega, which uses the following changes: NNRTI were scored 0.25 (with the exception of etravirine with a score of 0.5) for intermediate resistance, and ritonavir-boosted PI were scored 0.75 and 1.5 for intermediate resistance and susceptible, respectively. The Stanford algorithm uses 5 levels of resistance. We assigned the following scores to these 5 levels of Stanford: 0, 0.25, 0.50, 0.75, and 1 for respectively the high-level resistance, intermediate resistance, low-level resistance, potential low-level resistance, and susceptible. In a separate analysis we used the unweighted scores for Rega. We assigned the scores 0, 0.5, and 1 to the ‘resistant’, ‘intermediate’, and ‘susceptible’ groups for all drugs, respectively. The three systems did not include a score for ritonavir. We therefore excluded eleven TCEs that used ritonavir as only protease inhibitor, as we could not calculate a GSS of their treatment regimens.
The arithmetic sum of the individual score for the specific drugs provided the total GSS of that treatment. For brevity, we classified the total GSS score in the following categories: 0 to <1, 1 to <2, 2 to <3, 3 to <4, and ≥4. The 0 to <1 group contains viral sequences almost entirely resistant to the drugs in their regimen, and the ≥4 group contains viral sequences susceptible to more than 3 drugs given in their regimen.
To calculate the prevalence of drug resistance we used the mutation list published by the International AIDS Society USA (IAS-USA) [13] (link).
The arithmetic sum of the individual score for the specific drugs provided the total GSS of that treatment. For brevity, we classified the total GSS score in the following categories: 0 to <1, 1 to <2, 2 to <3, 3 to <4, and ≥4. The 0 to <1 group contains viral sequences almost entirely resistant to the drugs in their regimen, and the ≥4 group contains viral sequences susceptible to more than 3 drugs given in their regimen.
To calculate the prevalence of drug resistance we used the mutation list published by the International AIDS Society USA (IAS-USA) [13] (link).
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