Data Collection
Relevant clinical data, including age, sex, anthropometry, past medical history, and COVID-19 infection, were collected from the parents and electronic medical records. Overweight and obesity were defined by body mass index (BMI) > 23.5 and > 25 kg/m2 respectively9. The characteristics of COVID-19 infection included symptoms and severity classified based on National Institutes of Health (NIH) COVID-19 treatment guidelines9. Mild severity was defined by symptoms of upper respiratory tract infection (URI) (such as fever, cough, sore throat, headache or myalgia) and normal chest X-ray. Moderate severity was defined by symptoms of lower respiratory tract infection (such as increased respiratory rate, chest withdrawing or desaturation) or abnormal chest X-ray. All the chest X-rays were reviewed by radiologists outside the study at the time of diagnosis.
The definition of respiratory sequelae in this study refers to post COVID-19 symptoms or abnormal spirometry beyond four weeks after acute COVID-19 infection. Residual respiratory symptoms suggestive of post COVID conditions were assessed on interview with the parent one day before spirometry testing.
Pulmonary function was evaluated using spirometry. The testing was carried out by an experienced pediatric respiratory technician, adhering to the standardized procedures outlined by the ATS and ERS8,11. Forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and FEV1/FVC ratio are interpreted regarding the ATS/ERS spirometry impairments classification10. Abnormal pulmonary function is identified when FVC, FEV1 or FEV1/FVC ratio is less than lower limit of normal or z-score -1.64. Abnormal FEV1 and FEV1/FVC ratio are classified as obstructive impairment and abnormal FVC is classified as possible restrictive impairment. If spirometry shows obstructive impairment, a bronchial responsiveness test is performed by inhaling 400 micrograms of salbutamol, followed by repeating spirometry 15 minutes later.