The causes of fever and diarrhea are very complicated, and the common causes are bacterial infection, viral infection, inflammatory bowel disease, intestinal tumor and so on. 1. Bacterial infection: it can be caused by eating food contaminated by bacteria, such as bacillary dysentery, which is often manifested as fever and diarrhea, and the typical stools are mucous, pus and blood. 2. Viral infections, can be caused by viral infections of gastrointestinal dysfunction, also known as gastrointestinal colds, can be accompanied by fever, stools are often dilute watery. 3. Inflammatory bowel disease: if there are repeated diarrhea and fever, it is also necessary to be alert to the possibility of chronic diseases, such as ulcerative colitis, Crohn’s disease, etc., which can cause diarrhea and fever. 4. Tumor: If the elderly have low fever and change of stool character for a long time, they also need to consider intestinal tumors, and some of the patients may show diarrhea or constipation. Patients with fever and diarrhea need to seek medical treatment in time and systematic treatment under the guidance of doctors.