Distinctive patterns of gene expression in circulating leukocytes obtained from patients with acute respiratory infections. (A) In addition to the 30 classifier genes found to discriminate S aureus from E coli (Venn diagram, right: Sa from Ec; Figure 2; Table S6), we identified 30 genes that distinguish S aureus from S pneumoniae (Venn diagram, left: Sa from Sp; Figure S2; Table S10) and 45 genes that distinguish E coli from S pneumoniae (Venn diagram, bottom: Ec from Sp; Figure S2; Table S8). Only 3 genes were shared between either of these groups. (B) The 3 groups of genes found to discriminate samples from patients with bacterial infections shown in panel A were merged (102 unique genes, Venn diagram, left) and compared to the classifier genes used to discriminate influenza A from bacterial infections (35 genes, Venn diagram, right; Figure 1; Table S3). No genes were shared between these 2 groups. (C) The 137 classifier genes that discriminate influenza A from bacterial infections and the 3 groups of patients with different bacterial infections were merged and used to generate discriminatory patterns of expression among 27 patients with respiratory infections and 7 healthy volunteers. Values were normalized to the median expression of each gene across all donors. Clustering of conditions partitioned samples into 4 major groups. Four samples belonging to the influenza A group and one from the S aureus formed a distinct subgroup characterized by a mixed signature (*) and are listed in Table 1 (Figure 5C*).