What is the incidence of systemic inflammatory response syndrome (SIRS) in the US?

Updated: May 07, 2018
  • Author: Lewis J Kaplan, MD, FACS, FCCM, FCCP; Chief Editor: Michael R Pinsky, MD, CM, Dr(HC), FCCP, FAPS, MCCM  more...
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Answer

The true incidence of systemic inflammatory response syndrome (SIRS) is unknown but probably very high, owing to the nonspecific nature of its definition. Not all patients with SIRS require hospitalization or have diseases that progress to serious illness. Indeed, patients with a seasonal head cold due to rhinovirus usually fulfill the criteria for SIRS. Because SIRS criteria are nonspecific and occur in patients who present with conditions ranging from influenza to cardiovascular collapse associated with severe pancreatitis, [6] any incidence figures would need to be stratified based on SIRS severity.

Rangel-Fausto et al published a prospective survey of patients admitted to a tertiary care center that revealed 68% of hospital admissions to surveyed units met SIRS criteria. [7] The incidence of SIRS increased as the level of unit acuity increased. The following progression of patients with SIRS was noted: 26% developed sepsis, 18% developed severe sepsis, and 4% developed septic shock within 28 days of admission.

Pittet et al performed a hospital survey of SIRS that revealed an overall in-hospital incidence of 542 episodes per 1000 hospital days. [8] In comparison, the incidence in the intensive care unit (ICU) was 840 episodes per 1000 hospital days. It is not clear what percentage of patients with SIRS have a primary infectious etiology, allowing them to be classified as having sepsis. However, most likely the proportion of SIRS patients varies across patient and hospital groups, being highest for example in acute care settings and in those with immune deficiency.

The etiology of patients admitted with severe sepsis from a community emergency department was evaluated by Heffner et al, who determined that 55% of patients had negative cultures and that 18% were diagnosed with noninfectious causes that mimicked sepsis (SIRS). Many of the noninfectious etiologies required urgent alternate disease-specific therapy (eg, pulmonary embolism, myocardial infarction, pancreatitis). Of the SIRS patients without infection, the clinical characteristics were similar to those with positive cultures. [9]

Another study demonstrated that 62% of patients who presented to the emergency department with SIRS had a confirmed infection, while 38% did not. Within the same cohort of patients, 38% of infected patients did not present with SIRS. [10]

Still, Angus et al found the incidence of severe SIRS associated with infection to be 3 cases per 1,000 population, or 2.26 cases per 100 hospital discharges. [11] The real incidence of SIRS, therefore, must be much higher and likely depends somewhat on the rigor with which the definition is applied.


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