Respiratory tract infection is a more general concept or a generic term for a variety of diseases, including upper respiratory tract infections and lower respiratory tract infections. The main causes of respiratory tract infections include: 1, their own causes, that is, internal causes. This includes a transient decrease in resistance and immunity, such as those caused by cold or exertion, and the presence of immune deficiencies, such as tracheal transplants, immunosuppressive drugs, and acquired immunodeficiency diseases. 2. Invasion by a sufficient number of conditions, including bacteria, tuberculosis, viruses, fungi, mycoplasma, chlamydia, and parasites, when they reach a When a certain number or a specific part of the respiratory tract is reached, respiratory tract infection will occur, resulting in clinical symptoms.