First report on a foodborne outbreak of Streptococcus dysgalactiae Subsp. equisimilis in China.

Introduction: Streptococcus dysgalactiae subsp. equisimilis (SDSE), a Gram-positive, beta-hemolytic group G Streptococcus, possesses virulence factors such as M protein, streptolysin O, streptolysin S, streptokinase, and hyaluronidase. This study reports a foodborne outbreak caused by SDSE infection recently occurred in China.

Methods: In April 2019, an acute tonsillitis outbreak involving 155 patients occurred in a company in Changzhou, Jiangsu Province, China. Epidemiological surveys and laboratory investigations were conducted to identify the cause.

Results: All patients were clinically diagnosed with acute suppurative tonsillitis or acute pharyngitis. SDSE was identified as the causative pathogen, isolated form 81.4% (35/43) of patients, 12.5% (1/8) of canteen staff, and 33.3% (1/3) of tested food samples (fried meat). Multilocus sequence typing (MLST) and emm typing confirmed all isolates as ST98-stG480.0, suggesting contamination of fried meat by an SDSE-carrying canteen staff member as the source of the outbreak. The mean onset time was 45.8 h, with an SDSE prevalence rate of 27.2%.

Conclusions: This study is the first to report a foodborne outbreak caused by SDSE in Changzhou city since 2003. The identified strain, ST98-stG480.0, was exclusively associated with respiratory infections and exhibited no gastrointestinal symptoms. These findings underscore the importance of enhanced surveillance and in-depth investigation into the characteristics and public health implications of this strain.