FIGURE 1  Similarity in progression of severe viral and bacterial pneumonia. During viral and bacterial infection, the pathogens are recognised by host pathogen recognition receptors (PRR) on the surface of epithelial cells, mononuclear phagocytes and other cell types, resulting in initiation of various inflammatory cascades triggering systemic inflammatory response syndrome (SIRS). At this stage patients will have viral/bacterial sepsis with life-threatening organ dysfunction. Most individuals will clear the pathogen (with antimicrobial/antiviral therapy) and the body resolves the inflammation. Others, however, will not be able to clear the pathogen, or despite clearance of the pathogen will continue to exhibit dysregulated inflammatory responses that are unabated, resulting in tissue injury and organ failure. Of these patients, some receiving supportive care will recover and some will die.