BackgroundIn Taiwan, sequence type (ST) 239 and ST59 were two major clones among methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates in the past two decades. USA300 (ST8) prevailed in Americas but not in outside areas. Recently USA300 (ST8) emerged and were increasingly identified in Taiwan; we thus conducted an islandwide study to explore the role of USA300 among MRSA isolates. Methods100 MRSA bloodstream isolates identified in 2020, respectively, from each of the six participating hospitals in Taiwan were collected and characterized. First ten ST8 isolates from each hospital were further analyzed by whole genome sequencing (WGS). ResultsOf the 590 confirmed MRSA isolates, a total of 22 pulsotypes and 21 STs were identified. The strain of pulsotype AI/ ST8 was the most common lineage identified, accounting for 187 isolates (31.7%) and dominating in 5 of 6 hospitals, followed by pulsotype A/ ST239 (14.7%), pulsotype C/ ST59 (13.9%) and pulsotype D/ ST59 (9.2%). Of the 187 pulsotype AI/ ST8 isolates, 184 isolates were characterized as USA300 and clustered in three major sub-pulsotypes, accounting for 78%. Ninety percent of the 60 ST8 isolates for WGS were clustered in three major clades. ConclusionsIn 2020, USA300 became the most common clone of MRSA in Taiwan, accounting for > 30% of MRSA bloodstream isolates islanwide. Most of USA300 isolates circulating in Taiwan might be imported at multiple occasions and evolved into at least 3 successful local clades. MRSA USA300 had successfully established its role in Taiwan, an area outside of Americas.