Sepsis is a syndrome defined as life-threatening organ dysfunction due to a dysregulated host response to infection. Septic shock is a subset of sepsis, which describes circulatory, cellular, and metabolic abnormalities which are associated with a greater risk of mortality than sepsis alone (RCP 2017, The Sepsis Trust 2019, NICE CKS 2020).

There are some groups of people who are more vulnerable and higher risk of developing sepsis: very young (under one year) and older people (over 75 years), very frail people who have impaired immune systems because of illness or drugs, including people being treated for cancer with chemotherapy.