Susceptible population: children. Causes: Pathogens invade through the bronchi, causing inflammation of the fine bronchi, terminal fine bronchi and alveoli, often secondary to other diseases, common pathogens include Streptococcus pneumoniae, Staphylococcus, etc. Symptoms: sudden onset or delayed onset, fever, refusal of food or vomiting, drowsiness or irritability, wheezing and other symptoms, mostly cholera or regular fever, weak infants are mostly delayed onset, fever is not high, cough and lung signs are not obvious, common refusal of food, choking, vomiting. Imaging manifestations: X-ray shows increased and blurred lung texture in the middle and lower fields of both lungs, and patchy shadow of inflammatory lung texture; CT shows thickened bronchial vascular bundles in the middle and lower parts of both lungs, and nodular and lamellar shadows of different sizes with blurred edges are seen. Prevention: strengthen care and physical exercise in infancy should pay attention to nutrition, timely addition of side dishes, cultivate good dietary and hygienic habits, and avoid contact with patients with respiratory tract infections.