*2.4. Subtypes*

The proportion of sequences containing one or more PI-associated DRMs was similar in subtype B (20.0% of 570) versus non-subtype B (16.2% of 927; *p* = 0.07) sequences (Table 2). Of the 48 reported PI-associated DRMs, G73S was significantly more common in subtype B (3.1% of 927) than non-subtype B (0.4% of 570; adjusted *p* = 0.005) sequences. Of the 33 reported NP-TSMs, only L/M89T was significantly more common in non-subtype B than in subtype B sequences (8.4% of 570 vs. 0.4% of 927; adjusted *p* < 0.001). In subtypes A, C, G, CRF01\_AE, and CRF02\_AG, the consensus amino acid at position 89 is methionine (M) [41] and 89T requires just a single transition in these subtypes (ATG => ACG). In contrast, changing to 89T requires a one transition plus one transversion change in subtype B (CTN or TTR => ACN).
