Terminology. Bacteremia describes the presence of bacteria in the bloodstream - this may or may not make you ill (e.g. You are briefly bacteremic after brushing your teeth, but your body clears it). Septicemia is multiplication of bacteria in the blood (almost always associated with illness... But not always), and sepsis is the systemic response to infection.
See below. Bacteremia means having bacteria in the blood stream. Septicemia means invasion of the blood stream by microorganisms accompanied by chills, fever and prostration. Sepsis is sirs or systemic inflammatory response syndrome which is 2 or more of fever, rapid pulse, rapid respirations and elevated white count when they are caused by an infection.