Basically, all sepsis consists of is there being an infection in the bloodstream or tissues. Either bacteria or a virus is in the bloodstream and it can be very harmful if untreated.
Sepsis first causes high heart rate, high temperature, high respiratory rate and low white blood cell count. This is the body's reaction to fighting off the infection.
If not treated, the infection can spread to other organs, including the heart, lungs, kidneys, liver, brain and more. If other organs continue to get infected, the body eventually shuts down and the person dies.
Treatment for sepsis mostly consists of antibiotics being given to the infected individual.
Since most cases of sepsis are found before damage is done, sepsis is not a major, fatal infection; but it is serious in some cases, depending how long and the type of infection the individual has.