Objective  To identify the pathogen and infection source of an infectious diarrhea epidemic in a school in Fuyang, Anhui province, in 2021, and provide scientific evidence for the epidemic management and control.

  Methods  According to the epidemiological characteristics, the anal swabs, stool samples and vomit samples from the cases and food samples from the canteen were collected for the detection of pathogens. The strain identification, drug susceptibility test, virulence gene detection, pulsed-field gel electrophoresis (PFGE) and whole genome sequence analysis were conducted.

  Results  A total of 19 strains of Salmonella Enteritidis were isolated from the cases and food samples, all carried virulence genes (invA, sopE, agfA, spvR, hilA, stn, pefA). All the S. Enteritidis strains were resistant to nalidixic acid, 18 strains were resistant to ampicillin, tetracycline, cefotaxime, ceftazidime, ampicillin/sulbactam, and streptomycin and 7 acquired resistance genes and 1 target gene mutation were detected in 6 strains of S. Enteritidis, including aac (6')-Iy, aph (3)-Ib, aph (6)-Id, bla_TEM-1B, aac (6')-Iaa, sul2, tet (A) and gyrA (p.D87Y). The PFGE pattern bands of 19 strains of S. Enteritidis showed 100.00% similarity, all were ST11.

  Conclusion  The pathogen causing the epidemic of infectious diarrhea was S. Enteritidis, and the isolated strains showed high resistance to penicillin and cephalosporin. The infection source was dish golden crispy chicken chops. The mechanism of drug resistance was related to the carriage of bla_TEM-1B.