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. 2025 Jun 15;44(1):201.
doi: 10.1186/s41043-025-00957-5.

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

Junhong Li #  1 , Bowen Tu #  1 , Xujian Mao  1 , Ying Zhao  1 , Qiang Du  1 , Fengming Wang  1 , Cong Chen  1 , Hongbing Tang  1 , Junmin Ji  1 , Hongmei Yang  2
Affiliations

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

Junhong Li et al. J Health Popul Nutr. .

Abstract

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.

Keywords: Streptococcus dysgalactiae subsp. equisimilis; Foodborne; Outbreak; SDSE.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: Ethics was approved by Changzhou Center for Disease Control and Prevention. And informed consent was obtained for experimentation. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Biological mass spectrometry of one representative SDSE isolate in Changzhou, China
Fig. 2
Fig. 2
Phylogenetic tree inferred by analysis genes of the SDSE isolates in Changzhou, China and by the neighbor joining method in BioNumerics software versions 8.0. The marks which based on MLST were represented via MLST online analysis from SDSE database. The isolates were represented by circles connected and by branches proportional to the allelic distance. Colors represented types. Branches and numbers represented allelic differences between isolates
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