Lower respiratory tract infection ( LRl ) refers to inflammation of the trachea, bronchi, fine bronchi and lung tissue (including alveoli and interstitial lung), of which pneumonia is the number one infectious disease that seriously threatens pediatric health. One of the major pathogens of pediatric pneumonia is bacteria, and the judicious use of antibiotics often becomes the key to treatment. This section focuses on the rational use of antibiotics for acute tracheobronchitis, capillary bronchitis and pneumonia. I. Overview 1. Clinically diagnosed acute bronchitis also involves the trachea, so it can also be called acute tracheobronchitis. 2, The etiology of tracheobronchitis is both infectious and non-infectious. In addition, pediatric tracheobronchitis may also be a clinical manifestation of a variety of acute infectious diseases, such as measles, whooping cough, and influenza. 3. The main symptom of tracheobronchitis is cough, which is manifested as dry or sputum cough, and the variability of pulmonary retching sounds after coughing and sputum discharge is characteristic of the disease. The initial pathogen of infectious tracheobronchitis is mainly viral, including respiratory syncytial virus, influenza virus, parainfluenza virus, adenovirus, rhinovirus, etc. Bacteria are not the main causative agent. 2, immune deficiency, nutritional deficiency disease, pre-existing respiratory disorders (excluding asthma) such as bronchopulmonary dysplasia, immobile cilia syndrome, gastroesophageal reflux disease with recurrent aspiration in children, as well as small infants and children with a disease duration of ≥7d, the possibility of bacterial pathogens increases greatly. The main causative organisms are Streptococcus pneumoniae, Haemophilus influenzae, Catamorax and Staphylococcus, and occasionally other gram-negative bacilli. 3, Bacillus pertussis is still one of the important pathogens, especially in children under 3 months of age and over 7 years of age. 4, Mycoplasma pneumoniae is another important pathogen, occurring mostly during its epidemic period and in children over 5 years of age. Chlamydia is also an easily overlooked pathogen in pediatric tracheobronchitis.