Sepsis is a life-threatening emergency that happens when your body’s response to an infection that can lead to severe sepsis and septic shock. Sepsis damages vital organs and can cause death. In other words, it’s your body’s overactive and toxic response to an infection. Like strokes or heart attacks, sepsis is a medical emergency that requires rapid diagnosis and treatment.

You may have heard the term “blood poisoning” used instead of sepsis. Blood poisoning is not an accurate description of sepsis though. You can learn more about sepsis and why the term blood poisoning is no longer used here.

Your immune system usually works to fight any germs (bacteria, viruses, fungi, or parasites) to prevent infection. If an infection occurs, your immune system will try to fight it. It might be able to fight it alone or you might need help with medications such as antibiotics, antivirals, antifungals, or antiparasitics. Unfortunately, for reasons researchers don’t yet understand, sometimes the immune system stops fighting the “invaders,” and begins to turn on itself. This is the start of sepsis.

Some people are at higher risk of developing sepsis because they are at higher risk of contracting an infection. These include the very young (infants), the very old, those with chronic illnesses, and those with a weakened or impaired immune system. People who are malnourished can also contract infections more easily.

Patients are diagnosed with sepsis when they develop a set of signs and symptoms related to sepsis. Sepsis is not diagnosed based on an infection itself.

If you have more than one sepsis symptom, especially if there are signs of an infection or you fall into one of the higher risk groups, your doctor will likely suspect sepsis.

Sepsis progresses to severe sepsis when – in addition to signs of sepsis – there are signs that one or more organs aren’t working properly. This is called organ dysfunction and can include difficulty breathing (problems with the lungs), low or no urine output (kidneys), abnormal liver tests (liver), and changes in mental status (brain).

Septic shock is the most severe stage and is diagnosed when your blood pressure drops to dangerous levels. These patients are treated in the ICU and many physicians call them the “sickest people in the hospital.”

Sepsis is the number 1 cost of hospitalization in the U.S. Costs for acute sepsis hospitalization and skilled nursing are estimated to be $60 billion annually. This is only a portion of all sepsis-related costs, since there are often additional costs after discharge for many survivors, including rehabilitation, long-term care, medications, therapies, and more. The average cost per hospital stay for sepsis is double the average cost per stay across all other conditions. And, sepsis is one of the primary causes of readmission to the hospital.

Studies investigating survival and sepsis deaths have reported slightly different numbers, but it appears that on average, approximately 30% of patients diagnosed with severe sepsis do not survive. Up to 50% of survivors suffer from post-sepsis syndrome. Until a cure for sepsis is found, early detection and treatment is essential for survival and limiting disability for survivors.

Updated August 5, 2026.