Some patients with acute upper respiratory tract infection do not always have a fever. Acute upper respiratory tract infection is mainly caused by a decrease in the immunity of the body invaded by viruses, bacteria, mycoplasma, chlamydia and other pathogens, which causes an inflammatory response in the mucosa of the upper respiratory tract. However, the patient’s immune system is usually strong enough to heal on its own and the body temperature will return to normal. Some specific pathogenic infections, such as Staphylococcus aureus and influenza viruses, may cause fever to persist and require standardized medical intervention to gradually return the body temperature to normal.