Statistical analysis

The Kolmogorov-Smirnov test was first performed to test the normal distribution of the data. Normally distributed data are expressed as the mean ± standard deviation and were compared by t-tests. Abnormally distributed data are expressed as medians (interquartile ranges) and were compared by the Mann-Whitney U test or Kruskal-Wallis test. Categorical variables are presented as absolute numbers or percentages and were analyzed using the χ² test or Fisher’s exact test. Survival curves for up to 28 d after admission were generated using the Kaplan–Meier method and were compared by the log-rank test. IBM SPSS software (version 22.0, NY, United States) was used for statistical analyses, and P < 0.05 was considered statistically significant. To take into account the repeated nature of variables, analysis of variance (ANOVA) for repeated measurements of the general linear model was implemented. The statistical methods of this study were reviewed by Qiao Liu, a biostatistician from the Center for Disease Control and Prevention of Jiangsu Province in China.