Data collection and statistical analysis
Data were collected through a RedCap (Research Electronic Data Capture) program. Each site was identified with a number and the data of individual patients were entered anonymously.The clinical report form collected data on: gender, age, vital signs, diagnostic test performed at arrived (blood sample, chest X-ray, CT scan), signs orsymptoms (e.g. fever, diarrhea, chest pain, dyspnea),type of oxygen therapy during hospitalization and disposition (discharge, admission to ward, pediatric intensive care unit).The LUS report form collected data on presence/absence of short vertical artifacts, isolated or multiple B lines, white lung, consolidation < 1 cm or >1 cm, thickening of the pleural line, pleural effusion.Statistical analysis was performed using the SPSS software (IBM SPSS Statistics, version 24.0, Chicago, IL, USA).We tested the normality by Kolmogorov-Smirnovtest. The continuous variables were reported as the mean ± standard deviation (SD) or the median and interquartile range (IQR), as appropriate. Frequencies and percentages (%) were used to describe categorical variables.The Mann–Whitney test andStudent’sttest were used to compare nonparametric and normaldata, respectively, while Pearson’s χ2 test or a Fisher’s exact test were used, as appropriate. A p-valueinferior0.05 wasconsideredstatisticallysignificant.