Genomic analysis and clinical characteristics of a seasonal upsurge of Streptococcus pyogenes emm12.

PURPOSE: Streptococcus pyogenes cause invasive infections with variable incidence over time. In 2023, an increase in invasive S. pyogenes infections caused by emm-types 1 and 12 was reported globally. In Southern Sweden an increase in S. pyogenes emm12 severe infections was also noted and we set out to determine if this increase was caused by a single genetic sublineage. METHODS: Data on severe S. pyogenes infections notified between July 1st 2016 and June 30th 2023, including emm-types, was obtained from the Regional Centre for Communicable Disease Control. All emm12 isolates recovered during November-April each season were sequenced, analysed by core genome multilocus sequence typing (cgMLST), and compared with international emm12 isolates. Clinical information was obtained from the medical records. RESULTS: During the 2022/23 season, 157 cases of severe S. pyogenes infection were reported, of which 32 (20%) were caused by emm12 isolates. Forty-four emm12 isolates from 2016 to 2023 were analyzed. The patients had a median age of 45 years; soft tissue infection was the most common focus and two patients died. The isolates were genetically diverse and those recovered in the 2022/23 season did not form a closely related cluster. Instead, they were found among isolates from previous seasons and with international isolates, mostly from Denmark. There was no correlation between isolate clustering and type or severity of infection. CONCLUSION: The surge of emm12 infections recorded in Southern Sweden during the 2022/23 season was multiclonal, suggesting that host-related factors may have played a predominant role in the increased incidence of these infections.