Organisms That Cause Sepsis Are Changing, and Sepsis Management and Recognition Has Improved

Preface: Nice summary of the changing pathogenic organisms causing severe sepsis.  This summary also displays how improved sepsis recognition and management has decreased mortality from 40% to 28% over the last decade.

Mortality decreased from 40% to 28% overall. Although gram-negative organisms predominated, infection with an anaerobe or methicillin-resistant Staphylococcus aureus carried the highest mortality risk.

Recent studies suggest that mortality from severe sepsis is decreasing. But is this trend seen with all causative pathogens, and how large is the mortality reduction? Using data from the Nationwide Inpatient Sample — an administrative dataset approximating a 20% sample of all nonfederal, short-term, general, and specialty hospitals serving adults in the U.S. — researchers in California explored organism-specific severe sepsis mortality trends in the country from 1999 through 2008.

The data for 5,033,257 severe sepsis hospitalizations revealed that such hospitalizations had increased but that in-hospital mortality had decreased significantly — from 40.0% to 27.8% — over the study period. Among the 38.5% of cases for which the causative pathogen was reported, gram-negative bacteria predominated (51.5%; most commonly Escherichia coli and Pseudomonas), followed by gram-positive bacteria (45.6%; most commonly methicillin-sensitive Staphylococcus aureus and streptococci), anaerobes (1.7%), and fungi (1.2%). Although mortality was lower for cases with reported organisms than for those with unknown or unreported ones (26.6% vs. 36.1%), it declined similarly between groups over the study period.

After adjustment for demographic parameters, comorbidity, number of pathogens, and number of organ failures, mortality risk was highest overall for anaerobic organisms (hazard ratio, 1.31; 95% confidence interval, 1.23–1.40). Among gram-positive organisms, methicillin-resistant S. aureus was a significant predictor of mortality (HR, 1.38; 95% CI, 1.33–1.44). Gram-negative pathogens — particularly Pseudomonas and Serratia — carried the lowest risk.


Both the increase in severe sepsis hospitalizations and the impressive reduction in mortality are likely attributable to higher awareness and improved management of the condition following release of the Surviving Sepsis Campaign guidelines. That gram-negative pathogens are more common but less deadly is surprising and indicates a reversal of previous findings.


Ani C et al. Variations in organism-specific severe sepsis mortality in the United States: 1999–2008. Crit Care Med 2014 Sep 23; [e-pub ahead of print]. (

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