Prevalence of serotype switching in the overall population.

<p>The maximum likelihood phylogeny derived from a codon alignment of ‘core’ protein coding sequences is displayed, with fifteen monophyletic sequence clusters (SC1-SC15) labelled by arcs around the edge of the tree. Those sequence clusters in which no serotype switching was observed are marked by black arcs. Those sequence clusters in which multiple serotypes were observed are individually coloured, with the most prevalent serotype represented by light shading, and alternative serotypes indicated by darker shading or dashed lines.