The international and intercontinental spread and expansion of antimicrobial-resistant Salmonella Typhi

The emergence of increasingly antimicrobial-resistant (AMR) Salmonella enterica serovar Typhi (S. Typhi) threatens to undermine effective treatment and control. Here, aiming to investigate the temporal and geographic patterns of emergence and spread of AMR S. Typhi, we sequenced 3,489 S. Typhi isolated from prospective surveillance in South Asia and combined these with a global collection of 4,169 S. Typhi genomes. Our analysis revealed that independent acquisition of plasmids and homoplastic mutations conferring AMR have occurred repeatedly in multiple lineages of S. Typhi, predominantly arising in South Asia. We found evidence of frequent international and intercontinental transfers of AMR S. Typhi, followed by rapid expansion and replacement of antimicrobial-susceptible clades.