Mycoplasma pneumoniae is an acute inflammatory change of the respiratory tract and lungs caused by Mycoplasma pneumoniae, often accompanied by pharyngitis, bronchitis and pneumonia. Mycoplasma pneumoniae accounts for more than 1/3 of non-bacterial pneumonia or 10% of all causes of pneumonia. The incidence is higher in autumn and winter, but the seasonal differences are not significant. Mycoplasma pneumoniae is a parthenogenic, anaerobic, minimal microorganism that can live independently between bacteria and viruses. It is mainly transmitted through the respiratory tract and infects healthy people by inhaling oral and nasal secretions emitted by patients when they cough or sneeze, causing disseminated respiratory infections or small epidemics. Mycoplasma pneumonia is prevalent in children and young adults, and the possibility of interstitial pneumonia in infants should also be considered. Mycoplasma pneumoniae can be found in respiratory secretions from 2-3 days before the onset of illness until several weeks after recovery. The pathogen is usually found between the ciliated epithelium and does not invade the lung parenchyma, but adsorbs to the surface of the host respiratory epithelium through neuraminic acid receptor sites on the cell membrane, inhibiting cilia activity and destroying epithelial cells. The pathogenicity of Mycoplasma pneumoniae may be related to the patient’s allergic reaction to the pathogen or its metabolites. Pathology The lung lesions are lamellar or fused into bronchopneumonia, interstitial pneumonia, and fine bronchitis. The alveoli may contain a small amount of exudate and focal pulmonary atelectasis may occur. The alveolar wall and septum are infiltrated with neutrophils, monocytes, and plasma cells. The bronchial mucosa is congested, with swollen epithelial cells, cytoplasmic vacuole formation, necrosis and exfoliation. There may be fibrinous exudate and a small amount of exudate in the chest cavity. Clinical manifestations The incubation period is about 2-3 weeks, and the onset is usually slow. The symptoms are mainly malaise, sore throat, headache, cough, fever, loss of appetite, diarrhea, myalgia, and earache. The cough is mostly a paroxysmal irritating choking cough with a small amount of mucus. The fever may last for 2-3 weeks, and the cough may remain after the body temperature returns to normal. It is occasionally accompanied by retrosternal pain. Extra-pulmonary manifestations are more common, such as dermatitis (maculopapular rash and erythema multiforme). Physical examination may reveal a congested pharynx, occasionally tympanitis or otitis media in children, and enlarged cervical lymph nodes. Physical examination of the chest is often disproportionate to the extent of the lung lesion and may be unremarkable. Laboratory and other tests X-rays show infiltrative shadows in the lungs in various forms, with a segmental distribution, mostly in the lower lung fields, and some extending outward from near the hilum. The lesions often dissipate on their own after 3-4 weeks. Some patients present with a small amount of pleural effusion. The total blood leukocyte count is normal or slightly elevated, with predominantly neutrophils. About 2/3 of patients have a positive condensation set test with a titer greater than 1:32 2 weeks after onset of disease, which is more diagnostic if the titer increases gradually. About half of the patients were positive for the streptococcal MG agglutination test. The agglutination test is the traditional laboratory method for the diagnosis of Mycoplasma pneumoniae infection, but its sensitivity and specificity are not ideal. Determination of serum mycoplasma IgM antibodies (enzyme-linked immunosorbent assay is the most sensitive, immunofluorescence method is specific, and indirect hemagglutination method is more practical) can further confirm the diagnosis. Direct detection of Mycoplasma pneumoniae antigens in specimens can be used for early and rapid clinical diagnosis. Monoclonal antibody immunoblotting, nucleic acid hybridization and PCR techniques have the advantages of being highly efficient, specific and sensitive, which can be easily promoted and are of great value for the diagnosis of Mycoplasma pneumoniae infection. Treatment Early use of appropriate antibacterial drugs can reduce symptoms and shorten the course of the disease. The disease is self-limiting, and most cases can be cured spontaneously without treatment. Macrolide antibacterial drugs are preferred, such as erythromycin, roxithromycin and azithromycin. Fluoroquinolones such as levofloxacin, gatifloxacin and moxifloxacin, and tetracyclines are also used in the treatment of Mycoplasma pneumoniae pneumonia. The course of treatment is usually 2-3 weeks. Because Mycoplasma pneumoniae has no cell wall, antibacterial drugs such as penicillin or cephalosporins are ineffective. For those who choke violently, cough suppressants should be given appropriately. In case of secondary bacterial infection, targeted antibacterial drugs can be used for treatment according to sputum pathogenic examination.