Sepsis Infection: Definition, Symptoms & Criteria |

Sepsis Infection: Definition, Symptoms & Criteria

Instructor: Julie Waltz
In this lesson, we'll be looking at sepsis, the body's overwhelming response to certain infections. We will give a current definition of sepsis as well as symptoms and criteria to be considered when diagnosing sepsis. Updated: 09/10/2021

There's Something Rotten

Infectious disease is not a new thing. The concept of sepsis, derived from the Greek word for rot or decomposition, was first documented by Homer in his poems almost three millennia ago. A few hundred years later, Hippocrates also wrote about it as an odiferous, biological decay occurring in the body. Almost 2000 years went by before microorganisms were discovered to be the cause of infection and ultimately the cause of sepsis.


"The Third International Consensus Definitions for Sepsis and Septic Shock" was published in 2016 and contains a definition of sepsis (called Sepsis 3) as "a life-threatening organ dysfunction caused by a dysregulated host response to infection." Although the older terminology is still sometimes used, sepsis is now seen as a syndrome or spectrum of pathologic, physiologic, and biochemical abnormalities brought about by an infection, not as a continuum of sepsis to severe sepsis to septic shock. This change was made because it was recognized that there were too many terms used interchangeably and a definition and criteria for 'severe sepsis' were seen as redundant.

The need for new terminology arose because the definitions of sepsis and septic shock had not been revised for decades and many advances had been made in the management of sepsis as well as a better understanding of the pathophysiology and epidemiology of the condition. There was also a need to standardize the definition for research purposes.

Symptoms & Criteria

Sepsis is born out of an infection, but an uncomplicated infection is not sepsis. In other words, sepsis always involves an infection but an infection does not always involve sepsis. Infection is the trigger. Sepsis is a dysregulated, multifaceted response of the body to an infection. Common inciting infections include pneumonia, bloodstream infections (such as from skin contaminants or endocarditis), IV catheter-related infections, abdominal infections, urinary tract infections, and surgical wound infections. Initial symptoms of sepsis are related to the infection including fever, flushing, tachycardia, tachypnea, altered mental status, and hypotension.

Diagnostic Criteria:

There is no one clinical exam finding or test to measure a dysregulated host response. But there are examination findings and lab tests that can serve as indicators that a patient is in sepsis.


Organ dysfunction can be categorized by using the Sequential Organ Failure Assessment (SOFA). This is not meant to be a tool for patient management, but to clinically characterize a patient with sepsis. SOFA criteria include assessing respiratory parameters, coagulation tests, liver function tests, mean arterial pressure (MAP), the Glasgow Coma Scale score, kidney function tests, and urine output. Each of these values is given a score from zero to four with zero being the score for parameters within normal limits. An increase in the baseline SOFA score of 2 points or more means that the patient is experiencing worsening organ dysfunction.

There is a quick and easy version of SOFA that does not require any lab tests and can be done at the bedside as a quick diagnostic called Q SOFA which is a 3 component assessment system:

  • systolic blood pressure < 100 mm Hg
  • respiratory rate > 21
  • change in mental status or Glasgow coma score < 15


In the past, sepsis had also been diagnosed by using Systemic Inflammatory Response Syndrome (SIRS) criteria. These criteria are still sometimes used, however, SOFA scores were found to be better predictors of sepsis than SIRS criteria. SIRS criteria include:

  • tachycardia (HR > 90 bpm)
  • tachypnea (RR > 20 breaths/min)
  • fever (T > 38°C or T < 36°C)
  • leukocytosis (WBC > 12,000), leukopenia (WBC < 4,000) or bandemia (bands ≥ 10%)

Other Important Considerations

Also, remember that while all these evaluations are important and will guide the clinician to utilize necessary life-saving treatments, it is also important to identify the pathogen that instigated the infection so that the underlying infection can be treated appropriately. Pathogens can be bacterial, fungal, or viral. There are patterns and clues in patient characteristics and history that can aid in the recognition and differentiation between pathogens prior to definitive blood testing, thus preventing the overuse of non-specific, broad-spectrum antibiotics.

Septic Shock

Septic shock is still the most severe subset of the sepsis syndrome, where there is a very high risk of morbidity and mortality as the patient is hypotensive with profound circulatory, cellular, and metabolic abnormalities despite resuscitation. The three main variables identified for evaluating septic shock include:

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