External validation of bloodstream infection mortality risk score in a population-based cohort

Abstract

A risk score was recently derived to predict mortality in adult patients with Gram-negative bloodstream infection (BSI). The aim of this study was to provide external validation of the BSI mortality risk score (BSIMRS) in a population-based cohort. All residents of Olmsted County, Minnesota, with Escherichia coli and Pseudomonas aeruginosa BSI from 1 January 1998 to 31 December 2007 were identified. Logistic regression was used to examine the association between BSIMRS and mortality. Area under receiver operating characteristic curve (AUC) was calculated to quantify the discriminative ability of the BSIMRS to predict a variety of short-term and long-term outcomes. Overall, 424 unique Olmsted County residents with first episodes of E. coli and P. aeruginosa BSI were included in the study. Median age was 68 (range 0-99) years, 280 (66%) were women, 61 (14%) had cancer and 9 (2%) had liver cirrhosis. The BSIMRS was associated with 28-day mortality (p <0.001) with an AUC of 0.86. There was an almost 56% increase in 28-day mortality for each point increase in BSIMRS (OR 1.56, 95% CI 1.40-1.78). A BSIMRS ≥ 5 had a sensitivity of 74% and a specificity of 87% to predict 28-day mortality with a negative predictive value of 97%. The BSIMRS had AUC of 0.85, 0.85 and 0.81 for 7-, 14- and 365-day mortality, respectively. BSIMRS stratified mortality with high discrimination in a population-based cohort that included patients of all age groups who had a relatively low prevalence of cancer and liver cirrhosis.

Keywords: Bacteraemia; Pitt bacteraemia score; outcome; risk factors; sepsis.

Figure 1

Receiver operating characteristic plot of the bloodstream infection mortality risk score model of 28-day mortality * Area under the curve for the bloodstream infection mortality risk score model = 0.86

Figure 2

Calibration plot of bloodstream infection mortality risk score model for 28-day mortality * The observed frequency of 28-day mortality plotted by deciles of predicted probability from the bloodstream infection mortality risk score model (black line). Perfect calibration is represented by the grey Y=X line.

Figure 3

Predicted probability of 28-day mortality by bloodstream infection mortality risk score * Size of marker for point estimates is weighted approximately by the relative number of subjects with corresponding risk score.