If a person has had previous septicemia 5 years previous are they still susceptible?

Everyone is. Everyone is potentially susceptible to sepsis. Septicemia, or sepsis, is a body's reaction to an infection. So, potentially anyone can get sepsis. Whether you get it or not depends on a lot of things: genetics, type of infection, how long it has been untreated, etc. If you got it before, you may have a higher risk of getting it again. But, that depends also.
No. The risk factors for sepsis include: age (very young or very old), alcoholism, diabetes, leukemia, hiv, recent surgery, recent chemotherapy, and liver disease. Previous sepsis does not seem to be an independent risk factor.