Subjects
This study was a retrospective analysis of pediatric patients afflicted with SMPP and admitted to the hospital from June 2017 to January 2019. Diagnostic criteria of MPP were as follows: (1) fever, cough, and other clinical manifestations; (2) chest image findings indicative of pneumonia; (3) MPP-specific IgM antibody titer persisting at a level ≥ 1:320, or an antibody level that increased 4-fold during convalescent and acute SMPP phases (passive agglutination method, Fujirebio Inc., Japan). Based on MPP diagnosis combined with the latest diagnostic criteria for severe CAP in China, any one of the following criteria was used as a reference for the diagnosis of SMPP:5,6obvious shortness of breath or tachycardia (criteria: 1-5 years old, RR ≥ 40 times/min; >5 years old, RR ≥ 30 times/min, respectively); hypoxemia during inhalation and pulse oximetry-based oxygen saturation (SaO2) less than 0.93; chest images demonstrating multi-lobe or segment involvement or pulmonary area involvement of greater than 2/3 of the total lung area; pleural effusion, atelectasis, pulmonary necrosis, pulmonary abscess, and other pulmonary complications; complications associated with severe damage of other systems, such as central nervous system infection, heart failure, myocarditis, gastrointestinal hemorrhage, obvious electrolyte/acid-base balance disorder, etc. Exclusion criteria included previous congenital or secondary immunosuppression or defect, chronic pulmonary disease, kidney or cardiovascular disease, and connective tissue disorders, etc. Patients were also excluded if they were infected with other pathogens within 7 days post-admission or did not receive bronchoscopy at admission. All recruited children had received treatment with macrolide antibiotics for one week without noticeable improvement.