FIG 7.

Preadaptation of the average circulating HIV-1 polymerase sequence to North Americans by era. The colored portions of the bars denote the extent to which the average circulating HIV-1 sequence was preadapted (i.e., harbored HLA-specific polymorphisms) to that proportion of North American hosts in the population. Sequences from four eras were considered: the inferred MRCA sequence (foundation of the epidemic), reconstructed ancestral sequences (1965 to 1979), historic sequences (1979 to 1989), and modern sequences (2001 to 2011). The P value (P < 0.0001) for overall comparison was determined using the Friedman test. Sequences from individuals with known/suspected early infection were excluded from the analysis.