The non-specific and specific immune functions of the pediatric respiratory tract are poor, with poor cough reflex and airway smooth muscle contraction, as well as poor ciliary motility, making it difficult to effectively remove inhaled dust and foreign particles. Infants have low IgM, IgG, and IgA levels, and even lower SIgA, which is an important factor in respiratory mucosa resistance to infection. In addition, alveolar macrophage function is insufficient, and the amount and activity of lactoferrin, lysozyme, interferon, and complement are insufficient, so they are susceptible to various respiratory tract infections. In recent years, with the in-depth research on Mycoplasma pneumoniae (MP) by domestic and foreign scholars and the continuous improvement and development of laboratory diagnostic techniques, it has been confirmed that MP is one of the important pathogens of pediatric respiratory tract infections. Due to the long course of MP infection and the wide range of severity of the disease, parents and many physicians feel that there are some difficult choices in the diagnosis and treatment of this disease in the pediatric clinical work. Therefore, it is necessary for clinicians to have a comprehensive and correct understanding of pediatric MP infection, to evaluate and diagnose children in a timely manner, and to take correct preventive and curative measures to improve prognosis and prevent misdiagnosis and indiscriminate diagnosis. 1, the etiology of pediatric mycoplasma pneumonia Mycoplasma is a class of prokaryotic microorganisms without a cell wall that are bounded between viruses and bacteria. There are more than 80 known species of mycoplasma, which are widely present in humans and animals, most of which are not pathogenic. The main pathogenic mycoplasma in humans is MP, which can cause respiratory tract infections; others, such as Mycoplasma humanum and Mycoplasma solium, are also pathogenic and can cause genitourinary infections under certain conditions. This article is about pediatric MP infections. 2, the transmission route of pediatric mycoplasma pneumonia MP mainly through respiratory droplet transmission, usually seen in disseminated cases, the whole year has the onset, more in winter. A regional epidemic occurs about every 3-7 years and is characterized by a very long duration, which can last more than a year. In addition to MP pneumonia, it can also manifest as bronchitis, tracheitis and pharyngitis. Many outpatients have mild symptoms and are easily missed if serological tests are not performed. The disease is more frequent in school-age children and can also occur in preschoolers, and some of them can carry the pathogen for a long time after recovery. 3. Clinical manifestations of pediatric mycoplasma pneumonia 3.1 Incubation period Approximately 2 to 3 weeks (8 to 35 days). 3.2 Clinical manifestations vary in severity. Most children have a fever, anorexia, cough, chills, headache, sore throat, subxiphoid pain, etc. The body temperature may be persistent or flaccid fever, or only low fever, or even no fever. Most of the coughs are heavy, initially dry, followed by sputum secretion (occasionally containing small amounts of blood), and sometimes paroxysmal coughs slightly resemble whooping cough. Nausea, vomiting and transient maculopapular rash or urticaria are occasionally seen. There is usually no respiratory distress, but infants and children may have wheezing and dyspnea. Signs vary by age, with older children often lacking significant chest signs. In infants, mild turbid sounds on percussion, diminished breath sounds, wet rales, and sometimes signs of obstructive emphysema may be present. MP pneumonia may occasionally be combined with exudative pleurisy and lung abscess, and there is a relationship between chronic lung disorders (e.g., asthma) and MP. Hemolytic anemia is more common in the hematologic system; children with polyneuritis, meningoencephalitis, and cerebellar injury may also be seen; cardiovascular system lesions occasionally include myocarditis and pericarditis. Mixed bacterial infections may also be seen. Leukocyte levels vary, mostly normal, sometimes high. Blood sedimentation shows moderate increase. 3.3 X-ray examination Most of the lesions are unilateral, accounting for more than 80%, mostly in the lower lobe, sometimes only in the hilar shadow, mostly in the form of uneven cloudy pulmonary infiltrates, extending outward from the hilum to the lung fields, especially in the lower lobe of both lungs, with a few large lobar solid shadows and visible pulmonary atelectasis; often one place dissipates while new infiltrates occur elsewhere. Sometimes there is a bilateral diffuse reticular or nodular infiltrative shadow or interstitial pneumonia, without solid changes in the lung segments or lobes. Mild signs with prominent chest radiograph shadows are a characteristic feature of the disease. 3.4 Course The natural course of the disease varies from a few days to 2-4 weeks, with most fevers subsiding in 8-12 days and recovery taking 1-2 weeks. complete disappearance of the x-ray shadow extends for 2-3 weeks longer than the symptoms. Occasionally, recurrence is seen. 4, diagnosis of pediatric mycoplasma pneumonia The diagnosis of pediatric MP pneumonia is based on the child’s history, clinical manifestations and ancillary tests. Clinicians need to analyze these clinical data and sometimes combine them with the epidemiology of MP in order to make a correct and comprehensive diagnosis. The main points of diagnosis are: ① Persistent and severe cough, with x-ray findings being far more significant than physical signs. If several cases occur simultaneously in older children, an epidemic case is suspected and the diagnosis can be confirmed early. The white blood cell count is mostly normal or slightly elevated, the blood sedimentation is mostly increased, and the Coombs test is positive. ③ Penicillin, streptomycin and sulfonamides are ineffective. ④Serum cold agglutinin (IgM type) mostly titers up to 1:32 or higher, the positive rate of 50% to 75%, the more serious the disease, the higher the positive rate. Cold agglutinins mostly appear at the end of the first week after the onset of the disease, reaching a peak in the third to fourth week, and then decreasing and disappearing in two to four months. This is a non-specific reaction, also seen in liver disease, hemolytic anemia, infectious mononucleosis, etc., but its titer generally does not exceed 1:32. Adenovirus-induced pneumonia in older children, cold agglutinin is mostly negative. ⑤ Serum-specific antibody assay has diagnostic value and is often used clinically in complement binding test, indirect hemagglutination test, indirect immunofluorescence method and enzyme-linked immunosorbent assay; in addition, enzyme-linked immunosorbent assay can also be used to detect antigens. In recent years, monoclonal antibodies made from MP membrane proteins have been reported to detect antigens in specimens. The application of DNA probe and PCR to detect MP-DNA has the advantages of rapid and high specificity in diagnosis. (6) It takes too long to culture MP with patient’s sputum or pharyngeal swab lavage, often 2-3 weeks, so it is not very helpful for clinical purposes. At present, many experimental methods and reagents for the diagnosis of MP are still in the experimental research stage, and the accuracy, sensitivity and reliability of their clinical application are subject to clinical evaluation; there are still few reagents that have been certified by the Ministry of Health for popular clinical application. 5.Differential diagnosis of pediatric mycoplasma pneumonia The disease must sometimes be differentiated from the following diseases: ① tuberculosis; ② bacterial pneumonia; ③ whooping cough; ④ typhoid fever; ⑤ infectious mononucleosis; ⑥ rheumatic pneumonia. All of them can be differentiated according to medical history, tuberculin test, X-ray follow-up observation and bacteriological examination and serological reaction. 6, treatment of pediatric mycoplasma pneumonia The treatment of pediatric MP pneumonia is basically the same as the treatment principles of general pneumonia, taking comprehensive treatment measures. This includes general treatment, symptomatic treatment, application of antibiotics, adrenocorticosteroids, and treatment of extra-pulmonary complications. 6.1 General treatment 6.1.1 Respiratory isolation Because MP infection can cause a small epidemic, and the time to drain MP after the disease in children is long, up to 1 to 2 months beyond. In infancy, only symptoms of upper respiratory tract infection are manifested, and pneumonia occurs only after repeated infections. At the same time, it is easy to re-infect other pathogens during MP infection, leading to aggravation and prolongation of the disease. Therefore, respiratory isolation of the affected child or children with a history of close contact should be achieved whenever possible to prevent reinfection and cross-infection. 6.1.2 Care Keep the room air fresh and provide easily digestible, nutritious food and sufficient fluids. Keep the oral hygiene and respiratory tract unobstructed. Turn the child frequently, pat the back and change the position to promote the discharge of secretions, and aspirate appropriately if necessary to remove mucous secretions. 6.1.3 Oxygen therapy Oxygen should be administered in a timely manner to those with severe hypoxic manifestations or serious airway obstruction. The purpose is to increase the partial pressure of arterial blood oxygen and improve the tissue hypoxia caused by hypoxemia. The method of oxygen administration is the same as that for general pneumonia. 6.2 Symptomatic treatment 6.2.1 Expectoration The aim is to make sputum thin and easy to expel, otherwise it is easy to increase the chance of bacterial infection. However, there are few effective expectorants. In addition to strengthening turning, back patting, nebulization and sputum aspiration, expectorants such as phlegm-transforming Chinese medicine and amoxicillin can be used. As cough is the most prominent clinical manifestation of MP pneumonia, frequent and violent coughing will affect the sleep and rest of the child, so sedatives such as chloral hydrate or phenobarbital can be given appropriately. 6.2.2 Asthma For severe asthma, bronchodilators such as aminophylline can be used orally, 4-6 mg/(kg?), once every 6 h. Inhalation of albuterol can also be used. 6.3 Application of antibiotics According to the microbiological characteristics of MP, any antibiotics such as penicillin that can hinder the synthesis of microbial cell wall are ineffective. Therefore, for the treatment of MP infection, antibiotics that can inhibit protein synthesis should be used, including macrolides, tetracyclines, chloramphenicol, etc. In addition, lincomycin, clindamycin, vancomycin and sulfonamides such as SMZco are also available. The most commonly used antibiotics in clinical treatment are macrolides, such as erythromycin, spiramycin, methicillin, and leucomycin. Among them, erythromycin is preferred, and the drug is widely used and its efficacy is sure. It is obvious for eliminating the signs and symptoms of MP pneumonia, but the effect of eliminating MP is not ideal, and it cannot eliminate the parasitic of MP. The usual dosage is 50mg/(kg?d), and the milder cases can be treated orally in divided doses; in severe cases, intravenous administration can be considered; the course of treatment is generally advocated to be not less than 2-3 weeks, and it is easy to relapse if the drug is stopped too early. Erythromycin and erythromycin enteric-coated tablets are commonly used as oral agents. Erythromycin is mainly excreted by the bile, part of it can be reabsorbed from the intestine, and a considerable amount of erythromycin is metabolized and inactivated in the liver. 2.5% of the oral dose and 15% of the injectable dose are excreted in the urine as the active substance. Erythromycin is not removed from the body by either hemodialysis or peritoneal dialysis. When using erythromycin preparations, attention should be paid to its toxic effects. Various oral preparations can cause nausea, vomiting, abdominal pain, diarrhea and other gastrointestinal symptoms; thrombophlebitis can occur during intravenous infusion; occasionally allergic reactions occur, manifested as drug fever, urticaria, etc. It is worth noting that erythromycin jaundice often produces epigastric pain, nausea and vomiting, followed by fever, jaundice, leukocytosis and eosinophilia, increased serum bilirubin and transaminases in 14-21 d. After discontinuation of the drug, it can return to normal in 2-3 d, but the above symptoms can reappear again after re-dosing. In addition, the application of large doses of erythromycin may occasionally cause tinnitus and temporary hearing impairment, which generally occurs when administered intravenously or in those with reduced renal function and/or liver damage. Proliferative pyloric stenosis may occur after oral administration of odorless erythromycin in infants and children, and pseudomembranous enteritis has also been observed after oral administration of erythromycin. There is an increase in urinary catecholamines, 17-hydroxysteroids and serum transaminases, and a decrease in serum folate and urinary estradiol during erythromycin administration. If used with theophylline drugs, it has the effect of increasing the blood concentration of theophylline. Therefore, the use of theophylline drugs should be reduced or avoided when combined with theophylline drugs. In view of the high irritation of erythromycin to the gastrointestinal tract, and can cause an increase in blood bilirubin and transaminases, and there are reports of drug-resistant strains. The new products of macrolides, such as roxithromycin, clarithromycin, azithromycin, etc., which are easily tolerated orally, have strong penetrating ability, can penetrate into cells, and have long half-life, have been used. In recent years, azithromycin is commonly used clinically, which is relatively safe, the oral dose is 10mg/(kg?d), a single dose can be taken, and the children are more compliant; for children with severe disease, the treatment can be started with intravenous drip, and then changed to oral medication after the condition improves to consolidate the treatment. 6.4 Application of adrenocorticosteroids MP pneumonia is the immune response of the human immune system to MP lung infection. For children with rapid and serious development of the disease in the acute stage, or those with extended lung lesions and pulmonary atelectasis, interstitial fibrosis, bronchiectasis or extra-pulmonary complications, adrenocorticosteroids can be applied to reduce the inflammatory damage of the organism. Care should be taken to expel tuberculosis infection when applying hormones. 6.5 Treatment of extra-pulmonary complications Most scholars believe that the occurrence of extra-pulmonary complications is related to immune mechanisms. Therefore, in addition to active treatment of pneumonia and control of MP infection, hormones can be used according to the condition, and different symptomatic treatments are used for different complications. 7, the prevention of pediatric mycoplasma pneumonia problems Reasonable nutrition and moderate exercise can improve the child’s ability to adapt to the environment and help improve the body’s resistance to MP. Pay attention to keeping the environment clean, frequent ventilation of the child’s residence, and try to avoid contact with relatives who may carry MP, which can reduce the chances of MP infection. Prevention and treatment of malnutrition, rickets, anemia and other common underlying diseases in infants and children can also help reduce the infection rate of MP. For children with recurrent respiratory tract infections, some immune boosters can be taken appropriately under the guidance of doctors. Active development of MP vaccine is expected to reduce the rate of MP infection in the population. Most pediatric MP infections have a good prognosis, and although the course of the disease is sometimes long, complete recovery can eventually occur. Complications are rare, with only occasional otitis media, pleural exudate, hemolytic anemia, myocarditis, pericarditis, meningoencephalitis, and cutaneous mucosal syndrome. Occasional recurrences may occur, sometimes with slower recovery of pulmonary lesions and pulmonary function.