Abstract: AbstractObjective: To investigate the incidence and clinical characteristics of Clostridium difficile infection (CDI) in children with antibiotic-associated diarrhea (AAD), and to provide evidence for the diagnosis and treatment of antibiotic-related CDI. Methods: Inpatient clinical data of antibiotic-associated diarrhea from June 1st 2016 to October 1st 2017 were collected in Children's Hospital of Fudan University. Toxin A/B were tested and Clostridium difficile (CD ) was cultured. Neonates, incomplete information such as lack of fecal conventional bacteria culture and virus detection and the repeated cases were excluded . Toxin A/B(+) or the colonoscopy suggested pseudomembranous colitis cases were CDI group, the rest were in non-CDI group.Results: There were 150 patients with AAD. The incidence of CDI was 16.0%(24/150). The onset age of diarrhea was from one month ten days to 15 years 2 months old (median age 1.4 years old), among them boys were 103(68.7%) cases. ①Among 24 CDI patients, 22 children had acute diarrhea,1 had aggravated chronic diarrhea, because of Crohn's disease,1 had transitive diarrhea due to rectal polyp,11 (45.8%) had fever ,8(33.3%) had vomitus，2(8.3%) had abdominal pain,1 had abdominal distension ,1 had pseudomembranous colitis. ②There was no significant difference(P>0.05) in age of onset of diarrhea, gender, concomitant disease and antibiotic therapy two months before diarrhea between CDI group and non-CDI group. There was no statistic difference(P>0.05) in operations history, glucocorticoids and acid inhibitors therapy one month before suffering from diarrhea and lab index. The multiple factors Logistic models showed that clinical characteristics and routine laboratory test indicators had no statistically significant diffierence (P>0.05) between CDI group and non-CDI group.③The main treatments of AAD were to discontinue the broad-spectrum antibiotics, probiotics adjuvant therapy. If symptoms of CDI patients were not improved, metronidazole was the first choice.Failure to respond to metronidazole within 5-7 days should chang to vancomycin (oral) at standard dosing. The patients with symptomatic treatments of diarrhea were relieved in all CDI group，117 were improved in non-CDI group, 9 died of non-diarrhea. Only clinical performance and routine laboratory test indicators can't distinguish CDI and non-CDI among children AAD.Conclusion: The incidence of CDI of AAD patients was 16.0%. Fever and vomiting were the most common manifestations and prognosis was good. Only clinical performance and routine laboratory test indicators can't distinguish CDI and non-CDI among children AAD.