2.1 Study population
We collected and analyzed the medical records and chest radiographic findings of 269 children with PB, who were admitted to Respiratory Department of Tianjin Children’s Hospital from January 2016 to December 2019.
All the cases received FOB and bronchoalveolar lavage (BAL) procedure. If the fever does not subside, and the chest X-ray does not improve 2-3 days after the first FOB operation, the patient will receive multiple FOB and BAL treatments. Subjects were divided into the single FOB group and multiple group(≥2 times) according to the times of FOB treatment. The diagnosis of PB was determined according to discovery of inflammatory BCs by FOB, and further confirmed by pathology. Hypoxemia was defined as any recorded oxygen saturation of < 92% by pulse oximetry, measured on room air10. MP infection is determined by serologic or MP polymerase chain reaction (PCR) tests. An MP-immunoglobulin M (IgM) titer ≥1:160 or four-fold rising titer in acute and convalescent serum specimens were considered positive11.
Inclusion criteria : (1) All patients had an acute onset of fever and cough. (2) All patients met the criteria of type I PB confirmed by histopathology. Exclusion criteria: (1) patients who had underlying disease, such us congenital heart disease, asthma and congenital immunodeficiency disease. (2) patients who had history of inhalation of foreign body and confirmed by FOB as bronchial foreign body. (3) Patients who had incomplete medical records.