Changes in Group A Streptococcus subclones within three epidemics over time. The frequency distribution of all strains in the three epidemics is shown in grey, with three peaks of infection centered around 1995, 2000, and 2005. Ten major subclones (SC1 to SC10) were identified among the 344 strains collected between 1992 and 2007. The widths of the colored SC symbols show the temporal distribution of the SCs, and the heights are proportional to the annual abundance. Arrows between SCs indicate estimated relationships and give differences in the loci assessed . It can be seen that although there is some carry-over of lineages between epidemic peaks, new lineages arise and contribute to each epidemic.