Both viral and bacterial infections can cause fever, which can be identified by symptoms, auxiliary examinations, etc. In addition, it is necessary to note that there are many causes of fever. Both bacteria and viruses can act as exogenous heat sources, activating neutrophils, mononuclear macrophages and eosinophils in the blood, releasing large amounts of inflammatory factors, tumor necrosis factor and other substances, and triggering a rise in the hypothalamic thermoregulation point. The body elevates body temperature through skeletal muscle tremor, skin capillary contraction and other changes, causing fever. Viral infection fever is generally relatively low body temperature, relatively short time, laboratory examination of white blood cells are generally normal or low, lymphocytes are elevated; bacterial infection body temperature is relatively high amplitude, the duration of a longer period of time, laboratory examination can be seen in the total number of white blood cells, neutrophil count is elevated. The most fundamental method of identification is pathogenic examination, if there is coughing sputum, sputum culture can be carried out; if there is high fever, chills, blood culture can be checked. It should be noted that fever is not always caused by bacterial or viral infections, but other pathogens such as mycoplasma, chlamydia and other infections, blood diseases, connective tissue diseases, allergic reactions, malignant tumors and other causes may also cause fever, which need to be identified by a professional physician through detailed examination.