CXCL10 and viral infectious disease: This is the first diagnostic test based on soluble host-proteins to include both viral- and bacterial-induced biomarkers: tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which exhibits induced expression in viral infections and reduced expression in bacterial infection; interferon gamma-induced protein-10 (IP-10) that is induced to a greater extent in viral infections and lesser extent in bacterial infections; and CRP, which exhibits the opposite pattern to IP-10.