Phylogenetic analysis of 170 near–full-length unique respiratory syncitial virus fusion (RSV-F) gene sequences (nt 79–1602). Panels A and B are detailed phylograms of the RSV-A and RSV-B taxa analyzed, respectively. One bovine RSV-F sequence was added to the dataset (GenBank accession no. AF295543.1) as the outgroup (not shown) and used for rooting the phylograms. Topology was inferred by using the neighbor-joining method, and evolutionary distances were computed by using the maximum-composite likelihood method in MEGA5 software (www.megasoftware.net). The topologic accuracy of the tree was evaluated by using 1,000 bootstrap replicates. Only bootstrap values >50% are shown. Blue text and triangles represent RSV strains isolated in Canada and sequenced at the Centre de Recherche du Centre Hospitalier Universitaire de Québec; red branches indicates a sublineage of RSV-A with a N276S mutation; underlining indicates prototypical RSV A2 and RSV B1 strains. The clinical origin of strains from Canada (prospective study hospitalized patient [H] or clinic patient [C]; 2004–2005 palivizumab study patient [S]; retrospectively identified patient from the Montréal Children’s Hospital [MCH] or McMaster Children’s Hospital [MAC]) is indicated, followed by the year collected, the specimen identifier, and the result of RSV genogroup testing (RSV-A [A], RSV-B [B]) by multiplex PCR/DNA hybridization assay (14). Specimens with a nonsilent mutation at codon 272 have the amino acid substitution identified in brackets. When a taxon represents >1 identical sequences, the number of patients that it represents and the number of palivizumab recipients (PZB) among these patients are noted in parentheses. SA, South Africa; CHN, People’s Republic of China; UK, United Kingdom, JPN, Japan; AUS, Australia; USA, United States; CDC, US Centers for Disease Control and Prevention; NY, New York; SL, St. Louis; WV, West Virginia; MN, Minnesota; MD, Maryland; WA, Washington; SEL, Seoul, South Korea. Scale bars represent substitutions per basepair per the indicated horizontal distance.