first aligned the genome sequences of the 250 isolates against the NRCS-A reference genome CR01, resulting in a total of 22,621 single nucleotide polymorphisms (SNPs). To quantify recombination, we used ClonalFrameML 12 , which is specifically aimed at analysing whole-genome sequence data (see Supplementary Information). The results indicated that the impact of recombination (r) on the genome-wide substitution rate in S. capitis overall is almost equal to the impact of mutation (m), with r/m = 0.85. ClonalFrameML identified 190 recombination events in the global genealogy (Extended Data Fig. 1). The largest detected events (up to 26 kb) are probably products of horizontal gene transfer, some of which correspond to the insertion of pathogenicity islands. Clonal specialization and geographical dispersion of NRCS-A.The reconstructed maximum-likelihood tree (Fig. 1a) enabled us to draw a clear distinction between NRCS-A isolates that harbour the previously described specific NRCS-A pulsed-field gel electrophoresis pattern 8 (n = 197) and all the other strains found in basal positions (n = 53; hereafter 'basal'). These reconstructions revealed that this NRCS-A population is composed of at least three sublineages, which we named in chronological order of divergence on the basis of the observed branching order in the tree: 'proto-outbreak 1' (n = 18), 'proto-outbreak 2' (n = 17) and 'outbreak' (n = 162) (Fig. 1a,b). These three clades are supported both by bootstrap values greater than 95% and by the trimodal distribution of the

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