The diagnostic criteria of dry rales and croup can be heard in the lungs: Chlamydia pneumonia The clinical manifestations of this disease are non-specific and similar to those of Mycoplasma pneumonia. It is characterized by a slow onset, long duration and mild general symptoms, often accompanied by pharyngitis, laryngitis and sinusitis. After the symptoms of upper respiratory tract infection subside, dry and wet? sound and other manifestations of bronchitis and pneumonia. Cough symptoms may persist for more than 3 weeks. The white blood cell count is normal and the chest radiograph is nonspecific, mostly with unilateral lower lobe infiltrates, showing segmental pneumonia, or in severe cases, extensive bilateral pneumonia. Pathogenic examination is the same as for Chlamydia trachomatis pneumonia, and cell culture of aspirates from the trachea or nasopharynx is positive for Chlamydia pneumoniae. PCR detection of Chlamydia pneumoniae DNA is more sensitive than culture, but detection with pharyngeal swab specimens appears to be suboptimal and inferior to serological detection of Chlamydia pneumoniae specific antibodies. Micro-immunofluorescence (MIF) tests are still the most sensitive for detecting Chlamydia pneumoniae. Specific IgM antibodies ≥1:16 or IgM antibodies ≥1:512 or a 4-fold or higher increase in antibody titer have diagnostic value. Mild cases may be asymptomatic. Adolescents often have symptoms of pharyngitis, laryngitis, sinusitis, otitis media and bronchitis such as hoarseness, dry cough, sometimes fever and sore throat, which can last for weeks. The occurrence of pneumonia is usually mild and closely resembles the clinical presentation of Chlamydia pneumoniae infection and may be accompanied by extrapulmonary manifestations such as erythema nodosum, thyroiditis, encephalitis and Guillain-Barre syndrome. Pneumonia is more severe in adults, and hospitalization and respiratory support are often necessary, especially in the elderly. Some authors have found an association between Chlamydia pneumoniae infection and coronary artery disease by serological investigation, but this needs to be further established. In addition, the mechanism of asthma in Chlamydia pneumoniae infection is under investigation. Pulmonary X-rays of Chlamydia pneumoniae pneumonia often show a few foci of patchy infiltrates in subsections of the lung, with extensive solid changes seen only in severe cases. Most patients have normal blood leukocytes.