How long does it take for sepsis to kill you if untreated, and you are a sick elderly person?

Sepsis: Very variable. Depends upon the organism producing the sepsis, the therapy chosen and its timing and many other factors. Have seen patients die within hours of admission to hospital and others who linger for lengthy time periods.

Time can vary: Hours, days, or weeks depending on the infective organism. It also depends on the age of the individual and their general overall health.