Statistical analysis
Continuous data with a normal distribution were presented as mean ± standard deviation. If continuous data showed a skewed distribution, they were presented as a median [interquartile range (IQR)]. Frequency data are expressed as proportions. Comparisons of continuous variables were made using Student’s t test or the Mann-Whitney U test when appropriate, while differences in categorical variables were assessed using the X2 test or Fisher’s exact test, as appropriate.
Survival curves were plotted using the Kaplan-Meier method using a log-rank test. Multivariate logistic regression models were used to determine the independent risk factors for severe disease progression to critical illness during 28 days inpatient observation. Data were analyzed using SPSS 25.0. A two-tailed P value < 0.05 was considered statistically significant.