Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. The organ dysfunction is represented by an acute increase in the Sequential [Sepsis-related] Organ Failure Assessment (SOFA) score of 2 points or more (with the baseline assumed to be 0 in patients without any known pre-existing organ dysfunction).

Septic shock is a subset of sepsis in which particularly profound circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than with sepsis alone. Clinically they are identified by a vasopressor requirement to maintain mean arterial pressure of ≥ 65 mmHg and serum lactate level greater than 2 mmol/L (>18mg/dL) in absence of hypovolemia. Sepsis is the primary cause of death from infection, especially if not recognized and treated promptly.