Definition of termsa

Unique sequencesThe sequences within a set that possess at least one nucleotide difference among them in the region compared, i.e., the nonidentical sequences
SingletonOn a phylogenetic tree, a single sequence that is distant from other sequences due to possession of multiple nucleotide substitutions (≥4 nucleotide differences)
GenotypePreviously designated on the basis of phylogenetic analysis of the 2nd hypervariable region of G gene sequences; for RSV B, genotypes GB1 to -4, SAB1 to -4, and BA are included here; redefined here as showing >0.035 genetic distance from other sequences in the G gene ectodomain.
VariantOn a phylogenetic tree, a virus or group of viruses within a genotype that possesses ≥4 nucleotide differences in the G ectodomain region compared to other viruses and/or fall into a phylogenetic cluster away from the rest with >60% bootstrap statistical support
Newly introduced variantA virus or a group of viruses whose sequence was not observed in previous epidemics from the same study population that (i) cluster together with a bootstrap support value of >60% or (ii) have <4 nucleotide differences among themselves and have ≥4 nucleotide differences from other viruses classified as distinct variants
Persistent variantA virus (or a group of viruses) whose sequence(s) has <4 nucleotide differences in the G region from a variant detected in the immediate 1 or 2 preceding epidemics
  • a Definitions relevant to the G ectodomain region of the RSV genome we sequenced.