Genes showing no changes in expression levels (as compared to controls) are shown as black. Upregulated genes are shown in red with increasing intensities in proportion to the expression levels and in different intensities of green indicating levels of downregulation. Figure 3a shows cluster image of samples from mild and critically ill cases taken on admission. Seasonal flu sample (S21) showed a distinct gene expression pattern and formed a separate cluster (cluster 6) from all other samples. Three lung samples from critically ill patients also formed a separate cluster as most of the proinflammatory genes were upregulated (cluster 2). Remaining samples formed mixed clusters (cluster 4 and 5) which included both mild and critically ill patients. Overall, no distinct clustering pattern for the patients was observed for the severe and mild cases. With respect to gene clustering, clusters A and B contained genes associated with inflammation.