Inclusion Criteria:  Under the age of 18  Children diagnosed with diarrhea, including:  Acute diarrhea: infectious, such as viral bacteria, and non-infectious, such as improper diet and climate factors Persistent chronic diarrhea:  Including the following diseases:  Food allergy, food intolerance, indigestion, etc.; Inflammatory bowel disease (IBD); Diarrhoeal irritable bowel syndrome; Antibiotic associated diarrhea (AAD); Others: chronic hepatitis associated diarrhea, metabolic diseases associated diarrhea (such as diabetes mellitus with diarrhea), pancreatic exocrine dysfunction (cystic fibrosis), etc 3. Volunteered to participate in this study and signed the informed consent or the guardian signed the informed consent  Exclusion Criteria:  Class A infectious diseases associated with diarrhoea (cholera, plague) Children with congenital heart disease, immune deficiency, malformation of digestive tract, or with severe dysfunction of heart, lung, liver and kidney。 Children receiving long-term immunosuppressive therapy (except children with IBD)。 Children with gastrointestinal surgery and tumor; In addition to the above, the researchers determined that there were other children who were not suitable to participate in the study。