• Namwoo Heo, Jihee Lee, Yeonkyung Kim, Donghan Lee, Seok-Jae Heo, Yoon Soo Park, Jae-Won Yun, and Yong Chan Kim.
• Division of Infectious diseases, Department of Internal Medicine, Yongin Severance Hospital, Yonsei University College of Medicine, Yongin, Korea.
• J. Korean Med. Sci. 2023 Apr 17; 38 (15): e117e117.

BackgroundThe largest outbreak of enterohemorrhagic Escherichia coli (EHEC) O157:H7 occurred at a preschool in South Korea from June 12 to 29, 2020. This study aimed to analyze the epidemiological and clinical characteristics of EHEC infection in this outbreak.MethodsEpidemiological investigation was performed on all 184 children and 19 workers at the preschool using a standard questionnaire to assess symptoms, food intake, attendance, and special activity history. Pulsed-field gel electrophoresis analysis of confirmed cases was performed to determine genetic relevance.ResultsDuring this outbreak, 103 children were affected, whereas only one infection was identified in adults. Of the 103 pediatric patients, 85 had symptoms (82.5%), including diarrhea, abdominal pain, bloody stool, fever, and vomiting. Thirty-two patients (31.1%) were hospitalized, 15 (14.6%) were diagnosed with hemolytic uremic syndrome, and 4 (3.9%) received dialysis treatment. Pulsed-field gel electrophoresis analysis identified 4 genotypes with high genetic relevance (92.3%). Epidemiological investigation revealed that this outbreak might have occurred from ingesting foods stored in a refrigerator with a constant temperature above 10°C, which was conducive to bacterial growth. Despite several measures after outbreak recognition, new infections continued to appear. Therefore, the preschool was forced to close on June 19 to prevent further person-to-person transmission.ConclusionOur findings from the response to the largest outbreak will help prepare countermeasures against future EHEC outbreak.© 2023 The Korean Academy of Medical Sciences.

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