Traceability analysis of a foodborne disease outbreak caused by Clostridium perfringens in Ma'anshan City, Anhui Province, 2024.

Objectives: This study aimed to perform laboratory testing and traceability analysis of suspicious samples from a foodborne disease outbreak caused by Clostridium perfringens (C. perfringens) in a hospital in Ma'anshan City, Anhui Province, and to evaluate the application of whole-genome sequencing technology in the tracing of foodborne disease outbreaks. Methods: On-site epidemiological investigations were conducted, and suspicious biological, food, and environmental samples were collected. Patient biological samples underwent multi-pathogen screening. Following the epidemiological analysis, isolation, culture, and identification of suspected pathogens were carried out. Toxin gene detection and whole-genome sequencing were then performed on the isolated C. perfringens strains. Results: A total of 131 samples were collected during the outbreak. Among these, 20 anal swabs from patients with diarrhoea were tested for the nucleic acids of foodborne pathogens and five types of Diarrheagenic Escherichia coli. All samples tested positive for C. perfringens nucleic acid, while six samples also tested positive for enteropathogenic E. coli. Isolation and culture revealed that C. perfringens was detected in 41 samples, with a detection rate of 31.3% (41/131). Nucleic acid detection of six toxin genes (plc, cpb, cpe, Ia, etx, and netB) was performed on the 41 C. perfringens strains, with 29 strains testing positive for cpe. Whole-genome sequencing of the cpe-positive strains revealed identical ST sequence types and a maximum of 25 SNP differences, indicating a highly clonal group. Phylogenetic analysis of the core genome demonstrated homology among C. perfringens strains from patient anal swabs, canteen employees's anal swabs, and food samples. Conclusion: The outbreak was likely caused by contamination of Chinese food by C. perfringens from infected canteen employees. Whole-genome sequencing was instrumental in accurately tracing the source of the outbreak.