Fig. 4. High G-to-A branches can be associated with transmission clusters and, separately, can involve more than 100 mutations.

a, A cluster of 20 individuals emerging from a high G-to-A mutation event. This cluster involves a saltation of 25 mutations occurring within approximately one month, all of which are transition substitutions, with an elevated G-to-A rate. Sequences were annotated with age metadata suggestive of an outbreak in an aged care facility. Phylogenetic placement within the cluster is affected by missing coverage in some regions. b, Examples of further transmission clusters from the UK. Left, four sequences from the UK from February to March 2022 with 13 shared mutations with the high G-to-A signature. Right, a cluster of four sequences from the UK from February 2022 with 31 shared mutations with the high G-to-A signature. c, A sequence from Australia with a high G-to-A signature and a total of 133 mutations relative to the closest outgroup sequence. Just 2 of the 133 mutations observed were transversions; transitions included many G-to-A events. (In the month after this sequence was deposited, two additional related or descendant sequences, EPI_ISL_16315710 and EPI_ISL_16639468, were deposited, which may represent continued sampling from the same patient as they involve a substantial subset of shared mutations, but not full concordance, which is suggestive of complex intrahost evolution).