A, Cluster growth from 31 December 2007 to 31 December 2020 as a function of cluster size in 2007. Clusters where the most common acquisition risk group did not constitute >50% of all members were assigned to a combined (hyphenated) category consisting of the 2 most common risk groups in alphabetical order. B, Node growth from 31 December 2007 to 31 December 2020 as a function of node degree, that is, the number of links, in 2007. Abbreviations: Het, heterosexuals; IDU, intravenous drug users; MSM, men who have sex with men.