【病因】: 一、内因:呼吸道急性炎症在婴幼儿远较年长儿发病率高。主要因为婴幼儿各器官系统发育尚未成熟,特别是呼吸道的解剖生理特点,防御功能和神经系统的调节功能未臻完善,免疫功能低下,对外界环境的适应性差,易受环境或气候变化的影响,故易于感染,感染后也易扩散。此外如患营养缺乏症,先天性疾患和急性传染病等,机体抵抗力则更差、更易罹患呼吸道疾病,且得病后非常严 Etiology: First, the internal cause: acute respiratory tract inflammation in infants and young children is much higher than the incidence of older children. Mainly because infants and young children’s organ system development is not yet mature, especially the anatomical and physiological characteristics of the respiratory tract, defense and nervous system regulatory function imperfect, immune dysfunction, poor adaptability to the external environment, vulnerable to environmental or climate change , It is easy to infection, also easy to spread after infection. In addition, such as suffering from nutritional deficiencies, congenital disorders and acute infectious diseases, the body’s resistance is even worse, more susceptible to respiratory diseases, and get sick very strict