Fever is a normal reaction of the body when it encounters an infection or an abnormal situation, as long as it exceeds the body temperature of 37.4 ℃ is called fever. Fever is categorized as mild, moderate and severe depending on the temperature. A high fever is generally defined as a body temperature of more than 39 degrees Celsius. Fever can be combined with so many diseases, and it is a typical symptom of so many diseases, such as pneumonia, which can present with fever, chest pain, and coughing up rust-colored sputum. Some patients, such as those with biliary system diseases, can present with fever, nausea and abdominal pain. Fever is often combined with other symptoms, such as cough, shortness of breath or abdominal pain, nausea, etc. Depending on these accompanying symptoms, the diseases are different and can be treated accordingly.