Impact of extended spectrum beta-lactamase producing Klebsiella pneumoniae infections in severely burned patients

BACKGROUND: Significantly higher mortality has been demonstrated in patients who suffer severe burns complicated by Klebsiella pneumoniae bacteremia. The specific virulence mechanisms associated with this organism in this population are unclear. STUDY DESIGN: Our study assessed the impact of the mechanism of antibiotic resistance, strain clonality, and other host factors on morbidity and mortality. All patients with thermal burns infected with K pneumoniae between January 1, 2004 and July 1, 2008 were included in the analysis. RESULTS: Ninety-one patients had 111 episodes of K pneumoniae infections, with 59 isolates among the 91 patients producing extended spectrum beta-lactamase (ESBL). Patients with ESBL-producing strains were slightly younger, had higher Injury Severity Scores (ISS), and higher percent full thickness burns. Those who survived to discharge were younger (p < 0.001), had less burned surface area (p = 0.013), had fewer ventilator days (p = 0.016), and fewer infections with ESBL-producing isolates (p = 0.042). Logistic regression revealed that an infection with ESBL-producing K pneumoniae during the hospital stay was the factor most predictive of death, with a nearly 4-fold increased odds of dying. However, survival duration analysis of the population with and without ESBL-producing K pneumoniae using Kaplan-Meier technique showed no significant difference in the populations. Cox regression proportional hazards model revealed that only age (p = 0.01) and ventilator days (p ≤ 0.01) were associated with time to death. No specific clonality of the strains tested or ESBL production resistance genes were associated with mortality or ESBL production. CONCLUSIONS: These results suggest that infections caused by ESBL-producing K pneumoniae are predictive of death when occurring in an older, more badly burned population.