This study was conducted observationally. Infants were recruited from the Chengdu Women’s and Children’s Central Hospital between January 2019 and December 2020. This study was approved by the Ethics Review Board of Chengdu Women’s and Children’s Central Hospital 2016 (22). Written informed consent was obtained from the guardians of all participants. Included in the study were 30 infants who met the following criteria: 1) aged 1–3 years, 2) wheezing occurrence ≥2 times, 3) inhaled corticosteroids and antibiotics not administrated within one week, and 4) diagnosed with wheezing by a physician specializing in pediatric pulmonology. Of the 30 infants, 15 were found to be atopic. Atopy was defined based on skin prick test evidence (wheal diameter >25% induced by histamine) of sensitivity to ≥1 of 12 aeroallergens (allergen skin prick liquids; Aroger Company, Germany). Additionally, 18 children aged 1–3 years who underwent bronchoscopy due to foreign body aspiration within 24 h of sample collection were used as control subjects. Infants > 36 months of age with congenital heart diseases, immunodeficiency, bronchopulmonary dysplasia, cystic fibrosis, or neuromuscular disorders were excluded. Bronchoalveolar lavage (BAL) was performed using a fiberoptic bronchoscope through the airway via a laryngeal mask. BAL samples were collected from wheezing infants and controls, and centrifuged at 14000 × g for 10 min. The pellets were resuspended in 500 μL of phosphate buffered saline (PBS) and stored at -80°C until DNA extraction.
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