Multiple introductions and onward transmission of non-pandemic HIV-1 subtype B strains in North America and Europe.

Most HIV-1 subtype B infections in North America and Europe seem to have resulted from the expansion of a single pandemic lineage (B(PANDEMIC)) disseminated from the United States (US). Some non-pandemic subtype B strains of Caribbean origin (B(CAR)) may have also reached North America and Europe, but their epidemiological relevance in those regions remains largely unknown. Here we analyze a total of 20,045 HIV-1 subtype B pol sequences from the US, Canada, and Europe, to estimate the prevalence and to reconstruct the spatiotemporal dynamics of dissemination of HIV-1 B(CAR) strains in those regions. We find that B(CAR) strains were probably disseminated from the Caribbean into North America and Europe at multiple times since the early 1970s onwards. The B(CAR) strains reached the US, Canada and at least 16 different European countries, where they account for a very low fraction (<5%) of subtype B infections, with exception of the Czech Republic (7.7%). We also find evidence of the onward transmission of B(CAR) clades in the US, Canada, the Czech Republic, Germany, Italy, Spain and the UK, as well as short-distance spreading of B(CAR) lineages between neighboring European countries from Central and Western Europe, and long-distance dissemination between the US and Europe.