Sepsis does not arise on its own. It stems from another medical condition, such as an infection in the lungs, urinary tract, skin, abdomen (eg, appendicitis) or other part of the body. Invasive medical procedures like the insertion of a vascular catheter can introduce bacteria into the bloodstream and bring on the condition (NIGMS, 2013).
Many different types of microbes can cause sepsis, including bacteria, fungi, and viruses, but bacteria are the most common culprits. Severe cases often result from a body-wide infection that spreads through the bloodstream, but sepsis can also stem from a localized infection (NIGMS, 2013).
The causative organisms for sepsis have evolved over many years. Originally sepsis was described, and strongly considered to be, a disease specifically related to Gram-negative bacteria. This is because sepsis was thought to be a response to endotoxin—a molecule thought to be relatively specific for Gram-negative bacteria. In fact, some of the original studies of sepsis showed that Gram-negative bacteria were among the most common causes of sepsis. This resulted in a number of trials that focused on Gram-negative therapies, and even highly specific therapies for endotoxin, which were felt to be potentially useful treatments for sepsis.