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.