I. Characteristics of Mycoplasma pneumoniae infection: It mainly causes acute tracheobronchitis, capillary bronchitis, bronchopneumonia, interstitial pneumonia, lobar pneumonia, etc. The main features are as follows: 1. the airway mucosa is congested and edematous, with epithelial necrosis and detachment; 2. the infection is generally superficial, with the lumen filled with neutrophils and macrophages, and the lesions may also invade the submucosa and peribronchi, producing lymphocyte and plasma cell infiltration; 3. the alveoli may contain a small amount of mononuclear cell-based exudate, and focal pulmonary atelectasis, pulmonary solidification, and emphysema may occur; 4. capillaries markedly congested, and the interstitium of the lung is infiltrated mainly by neutrophils and large mononuclear cells. The incubation period of Mycoplasma pneumoniae infection averages 2.5 weeks (4 days to 3 weeks), and long-term incubation is an important diagnostic basis for it. Mycoplasma pneumoniae is mainly transmitted by droplets between close contacts over a long period of time, and the pathogen can be excreted 2-8 days before the onset of the disease, and is also infectious during the acute phase. The clinical manifestations of Mycoplasma pneumoniae infection: 1. The initial symptoms are similar to influenza, with peripheral discomfort, sore throat and dry cough. As the disease progresses, the symptoms worsen and a paroxysmal cough may appear, and the cough has mucus-like or mucopurulent or blood-stained sputum. 2. The development of the disease is slow, and the acute symptoms usually last for 1 to 2 weeks with gradual recovery, and there may be malaise and general discomfort for several weeks. 3, symptoms are generally mild, usually self-healing, the course of the disease about 1 to 3 weeks, but a few patients have severe pneumonia. 4. Mycoplasma pneumoniae infection can cause asthma. Mycoplasma pneumoniae infection can trigger asthma attacks or aggravate asthma attacks and prolong the course of the disease; mycoplasma pneumoniae infection accounts for about 50% to 62% of children with first asthma attacks and about 20% to 50% of children with acute asthma attacks, and chronic infection will lead to airway remodeling; chronic mycoplasma pneumoniae infection can also lead to increased secretion of Th2-type cytokines, causing small airway constriction and inflammatory cell infiltration, which in turn can lead to increased secretion of Th2-type cytokines and increased airway contraction. Chronic infection with Mycoplasma pneumoniae can lead to increased secretion of Th2 cytokines, causing small airway constriction and inflammatory cell infiltration, thereby exacerbating the chronic inflammatory response and hyperresponsiveness of the airways in asthmatic patients. (5) Extra-pulmonary complications are common and include: pharyngeal and tympanic membrane congestion, rarely rash, superficial lymph node enlargement, gastroenteritis, pericarditis, myocarditis, hepatitis, nephritis, nephropathy, encephalitis, meningitis, etc.