Fig. 1

Diagram illustrating multiple clusters of transmissibility. There are three variants in the source (S1, S2 and S3). The lines represent one-step mutation, showing that S1 is very close to recipients Ra and Rb, whereas S3 is very close to recipients Rc and Rd. If we use the arithmetic mean of the genetic distances, all three sequences would get the same value (3), which would assign an artificially low value to S2. If we use the harmonic mean instead, S1 and S3 have a smaller value than S2 (1.5 vs 2)