Sepsis: The presence of bacteria (bacteremia), other infectious organisms, or toxins created by infectious organisms in the bloodstream with spread throughout the body. Sepsis may be associated with clinical symptoms of systemic illness, such as fever, chills, malaise, low blood pressure, and mental-status changes. Sepsis can be a serious situation, a life-threatening condition that requires urgent and comprehensive care. Treatment depends on the type of infection but usually begins with antibiotics or similar medications. Also known as blood poisoning and septicemia.