4. Statistical analysis
All data were analyzed with SPSS Statistics Software (version 26; IBM, New York, USA). The statistics for categorical variables were summarized as frequencies and percentages and were compared using Chi-square test or Fisher’s exact test between different groups where appropriate. Continuous variables were described using median (IQR) and compared using Mann-Whitney U test. To explore the risk factors associated with disease severity, univariable and multivariable logistic regression models were used to estimate odds ratios and the 95% confidence intervals. A two-sided α of less than 0.05 was considered statistically significant.