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Age distributions by categories of sequence types and by four high-isolation-frequency sequence types. (a): Age distribution classified by classes of STs. (b): Age distribution classified by four high-isolation-frequency STs: ST95, ST131, ST73 and ST357. Note the two peaks for the 20–30s and 50–70s shown in all categories of sequence types. HIF, high-isolation-frequency ;MIF, middle-isolation-frequency; SIF, single-isolation-frequency; ST, sequence type.
