What is sepsis?

Sepsis is a person’s overwhelming or impaired whole-body immune response to an insult—an infection or an injury to the body, or something else that provokes such a response. It’s a serious condition and a leading cause of death in hospitals. It’s also a main reason why people are readmitted to the hospital.

Sepsis occurs unpredictably and can progress rapidly. In severe cases, one or more organ systems fail. In the worst cases, blood pressure drops, the heart weakens, and the patient spirals toward septic shock. Once this happens, multiple organs—lungs, kidneys, liver—may quickly fail, and the patient can die.

What causes sepsis?

Most sepsis is caused by bacterial infections, but it can also be caused by viral infections, such as COVID-19 or influenza; fungal infections; or noninfectious insults, such as traumatic injury. Normally, the body releases chemical or protein immune mediators into the blood to combat the infection or insult. If unchecked, those immune mediators trigger widespread inflammation, blood clots, and leaky blood vessels. As a result, blood flow is impaired, depriving organs of nutrients and oxygen and leading to organ damage. Noninfectious insults can lead to sepsis because they can activate the body’s immune responses just like infections do. In some cases, the cause can no longer be determined, particularly when a patient is given antibiotics, which can make infectious agents no longer detectable.

Many small oblong shapes, some making up brightly colored clusters.

White blood cells undergoing a cascade of biochemical changes that is part of the immune response. Credit: Xiaolei Su, HHMI Whitman Center of the Marine Biological Laboratory.

Who gets sepsis?

Anyone can develop sepsis. The people at highest risk are infants, children, older adults, and people who have underlying medical problems such as diabetes, AIDS, cancer, or liver disease; have concurrent injuries or surgeries; or are taking certain medications. There are also unknown biological characteristics in the body that may increase or decrease a person’s susceptibility to sepsis and cause some people to decline more rapidly while others recover quickly. Scientists are conducting studies to identify these individual factors.

In the foreground, a monitor showing heart rates and other vital signs of four people. In the background, patients in hospital beds.

Credit: iStock.

How many people get sepsis?

Each year, according to the Centers for Disease Control and Prevention (CDC), at least 1.7 million adults in the U.S. develop sepsis, and nearly 270,000 die as a result. The number of sepsis cases per year in the U.S. has been on the rise, likely due to several factors:

  • There is increased awareness and tracking of sepsis, so more cases may be recognized than they were previously.
  • People with chronic diseases are living longer. Sepsis is more common and more dangerous in those with other illnesses and in older adults.
  • Some infections can no longer be eliminated with antibiotic drugs. Antibiotic-resistant infections can lead to sepsis.
  • Organ transplants are more common. People are at higher risk for sepsis if they’ve undergone any procedure that requires the use of medications to suppress the immune system, including organ transplantation.

What are the symptoms of sepsis?

Common symptoms of sepsis are fever, chills, rapid breathing and heart rate, rash, confusion, and disorientation. Many of these symptoms are also common in other conditions, making sepsis challenging to recognize, especially in its early stages.

How is sepsis diagnosed?

Doctors start by checking for the symptoms mentioned above. They may also test a person’s blood for the presence of bacteria or an abnormal number of white blood cells, or use a chest X-ray or a CT scan to locate an infection. In addition, they can use a scoring system to determine if the function of a particular organ is declining and note the number of organ systems affected.

How is sepsis treated?

Doctors typically treat people with sepsis in hospital intensive care units. They try to stop an infection, protect vital organs, and prevent a drop in blood pressure. This almost always includes the use of antibiotic medications and fluids. More seriously affected patients might need a breathing tube, kidney dialysis, or surgery to remove an infection.

Despite years of research, scientists haven’t yet been successful developing an approved medicine that specifically targets the aggressive or impaired immune response seen with sepsis. Sepsis patients vary in their immune responses and in their responses to treatment due to individual differences. Scientists are trying to find new therapies and to determine which patients are likely to benefit most from a certain approach.

More information about the symptoms, diagnosis, and treatment of sepsis is available from the CDC.

Doctors with a patient on a gurney.

Credit: iStock.

Are there any long-term effects of sepsis?

Many patients who survive severe sepsis recover completely, and their lives return to normal. But some people can have permanent organ damage. For example, in someone who already has impaired kidneys, sepsis can lead to kidney failure that requires lifelong dialysis. If sepsis affects the brain, a person may have problems with thinking, memory, or concentration.

There’s also some evidence that severe sepsis permanently disrupts a person’s immune system, placing them at greater risk for future infections. Studies have shown that people who have experienced sepsis may have a higher risk of various medical conditions or death, even several years after the episode.

More information about the long-term effects of sepsis is available from the CDC and the Journal of the American Medical Association’s Patient Page.

What is the economic cost of sepsis?

Estimates vary, but the costs of sepsis treatment can be quite substantial. Treatment often involves a prolonged stay in the intensive care unit and complex therapies. People with sepsis are two to three times more likely to be readmitted to the hospital than people with many other conditions, such as heart failure or chronic obstructive pulmonary disease. Development of sepsis may also be linked with other illnesses like pneumonia.

What research is being done on sepsis?

The National Institutes of Health (NIH) supports many studies focused on sepsis (visit the NIH RePORTER database), some of which are clinical trials that will evaluate the effectiveness of potential treatments. Other scientists seek molecular clues in patients’ blood that could diagnose sepsis early or predict who might be more prone to the condition, allowing doctors to prevent it. Some try to find ways to estimate when and how a sepsis patient’s condition will decline, or if a certain therapy is appropriate for particular patients. Still others examine sepsis in specific populations, such as premature babies; people with known risk factors, such as diabetes, cancer, or kidney or liver disease; or long-term sepsis survivors.


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NIGMS is a part of the National Institutes of Health that supports basic research to increase our understanding of biological processes and lay the foundation for advances in disease diagnosis, treatment, and prevention. For more information on the Institute’s research and training programs, visit https://www.nigms.nih.gov.

This page last updated on 9/10/2021 10:39 AM