Fever is most commonly associated with respiratory tract infections, but not all fevers are caused by respiratory tract infections. Many unexplained clinical fevers involve a variety of diseases, including respiratory, urinary, digestive, and immune system disorders, so it is important to identify the cause of the fever. Many clinical viral infections can cause symptoms of fever. For example, in the most common form of influenza, patients often develop a high fever without other symptoms. A detailed examination may reveal a congested throat wall or even enlarged tonsils. If the patient has a history of unclean sexual life, the presence of unexplained fever must be taken seriously and should go for an infection screening eight to exclude infectious diseases such as AIDS, syphilis, gonorrhea, hepatitis, etc. Some digestive system diseases, such as acute gastroenteritis, do not have any cold symptoms, but symptoms such as diarrhea, fever, nausea and vomiting can occur. In addition to this, there are some unexplained low fever, such as tuberculosis patients who may have prolonged low fever without other respiratory symptoms, and some malignant tumor patients who often have fever as the first symptom, which may be accompanied by weight loss, poor diet and other manifestations. When there are no symptoms of cold but fever, patients must be cautious. Because fever is a symptom manifested by a disease in one of the body systems, it needs to be combined with clinical examination to clarify the cause before it can be cured.