Inclusion Criteria:  Patients undergoing appendectomy due to appendicitis; 6-36 months after appendectomy; Patients with no obvious abnormality observed by colonoscopy; Age between 20 and 85.  Exclusion Criteria:  A. Any history of malignancy or disease Any inflammatory bowel disease (IBD) prior to study inclusion; Antibiotics and hormone drugs taken within the last three months; Patients with severe systemic diseases (severe diabetes, hypertension or autoimmune diseases, etc.); Severe clinical symptoms of digestive tract (severe diarrhea, constipation, purulent disease, etc.) within half a year.