Trends of resistance of Gram-negative bacteria in the ICU during a 3-year period

Introduction

The aim of the study was to calculate the incidence of bacteremias due to multidrug-resistant (MDR) Gram-negative bacteria (GNB) and to detect any emerging trends during a 3-year period.

Methods

A prospective study of bloodstream infections in an ICU of a tertiary care hospital. The data collected prospectively included epidemiological and clinical characteristics of all patients admitted to the ICU from September 2004 to August 2007, the bacteria isolated from bloodstream infections and their patterns of resistance. A bacterium was characterized as MDR when it was resistant to three classes of antibiotics and as MDRc when it was also resistant to carbapenems. The study was divided into nine 4-month periods in order to calculate the incidence of MDR bacteremias in each such period and to evaluate each bacterium separately.

Results

During this study 390 patients were admitted to the ICU, of whom 60% were male. Their mean age was 65 years, the mean APACHE score was 17.9 and the mean duration of stay in the ICU was 18 days. One hundred bacteremias due to MDR GNBs were recorded. Of the isolated MDR bacteria, 77 were MDRc and 95% of those 77 were Acinetobacter baumannii (25 isolates), Pseudomonas aeruginosa (20 isolates) or Klebsiella pneumoniae (28 isolates). A clear trend emerged for K. pneumoniae, whose incidence increased exponentially during the study period. Of the 28 isolates of MDRc K. pneumoniae, 7% were recorded during the first 12 months of the study, 33% during the next 12 months and 60% during the last 12 months. The incidence of A. baumannii remained relatively stable (36%, 32% and 32% of isolates were recorded during each 12-month period) and the same was true for P. aeruginosa (25%, 40% and 35%, respectively).

Conclusion

The incidence of bacteremias due to MDR GNBs that are also resistant to carbapenems is high in our ICU. Bacteremias due to MDRc K. pneumoniae have risen dramatically during the past months. Further studies are needed to investigate the risk factors and develop strategies to confront the problem.