Emergence and spread of moxifloxacin-resistant ribotype 231 in Sweden between 2006 and 2015.

An aggregation of moxifloxacin-resistant ribotype 231 (RT231) isolates was first identified in the county of Stockholm in 2008, and by the end of 2015 isolates of RT231 had spread to 13 of 21 Swedish counties. We investigated the epidemiology of RT231 in Sweden between 2006 and 2015 using whole genome sequencing (WGS) and evaluated whether its emergence could be associated with extended moxifloxacin use. We performed WGS and phylogenetic analysis of 51 RT231 strains isolated in Sweden over a 10-year period. We also calculated the county-specific prescription rates for moxifloxacin between 2005 and 2015. Using WGS and detailed single nucleotide polymorphism analysis, we demonstrated three divergent sublineages of moxifloxacin-resistant RT231 in Sweden from 2008 to 2015. A set of closely related RT231 was identified in hospitals located in the counties of Stockholm and Uppsala in 2008. Another set of RT231 isolates was found in four different counties in the Uppsala-Örebro Health Care Region. A gradual drop in moxifloxacin use in the county of Stockholm coincided with a reduction of RT231 in the area. However, RT231 continued to be frequent in surrounding counties including Uppsala, a county that also had the highest moxifloxacin prescription rates. We demonstrated frequent transmission of RT231 within and between counties, indicating the importance of careful monitoring of hospitalized individuals infected with moxifloxacin-resistant as well as the need for a strict moxifloxacin prescription policy.