High fever in a patient can be caused by either an infection or something other than an infection. Infectious fever is when a patient’s fever is caused by an infection with a pathogenic microorganism. Pathogenic microorganisms include bacteria, viruses, mycoplasma, chlamydia, spirochetes, fungi, protozoa, helminths, etc. Whether the infection is bacterial or viral, the patient may have a high fever, and in turn, a high fever may be caused by a bacterial infection or a viral infection. In the case of high fever, if the patient has pus spots on the tonsils, yellow pus nasal discharge, yellow pus sputum or pus draining from puncture; significantly increased inflammatory indicators such as total white blood cell and neutrophil ratio, C-reactive protein and calcitoninogen in routine blood tests, more white blood cells and white blood cell tubular type in routine urine, pus cells detected in routine stool; significantly increased white blood cells and neutrophils in routine pleural fluid, ascites and cerebrospinal fluid. Or pathogenic bacteria were cultured in blood, urine, feces and pleural fluid, ascites and cerebrospinal fluid, etc., which all support that the patient’s hyperthermia was caused by bacterial infection.