Statistical analysis
Before commencing any statistical processing and analysis, data were visually inspected and checked for outliers. The analysis was performed using the commercial software Statistical Package for Social Science (SPSS version 24.0, IBM, Chicago, IL, USA). Categorial variables were tested using the chi-square test or Fisher’s exact test, as appropriate. Continuous variables were examined using the student’s t test if normally distributed and Man–Whitney test if not. To identify variables associated with the primary outcome measure, univariate analysis was performed. Variables that were significantly associated (p<0.05) with the primary outcome measure (defined as the composite endpoint of death or requirement for mechanical ventilation during hospitalization) were entered into the multivariate logistic regression model in a stepwise fashion. Adjusted odds-ratios (ORs) and 95% confidence intervals (CIs) for the likelihood of occurrence of primary outcome measure were calculated. Statistical significance was set at p-value less than 0.05.