Statistical analysis
The statistical analysis was performed using GraphPad Prism 6. Categorical variables are reported as frequencies and percentages. Continuous variables are reported as mean ± standard deviation (SD). Categorical variables were compared using Chi square test. For comparison between severe and critically severe patients, the Mann-Whitney U test was used. One-way ANOVA followed by Tukey’s test was used for statistical comparisons between healthy subjects, severe and critically severe group.