Comparison of bloodstream infections in intensive care unit patients, due to different Gram-negative bacteria

Introduction

To compare the incidence and risk factors of bloodstream infections (BSIs) due to Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae and to assess which of them is associated with higher mortality in ICU patients.

Patients and methods

This study was conducted in the 28-bed multidisciplinary ICU of Evangelismos Hospital in Athens, during an 18-month period (August 2004–January 2006). All ICU patients with blood cultures due to A. baumannii or P. aeruginosa or K. pneumoniae bacteremia, obtained >48 hours after ICU admission, were studied. Patients with BSIs due to more than one of those three pathogens were excluded. Information included patients' age, gender, underlying disease, admission category, hospitalization before ICU admission, length of ICU stay, source of BSIs and ICU mortality were compared. The illness severity was assessed by APACHE II score on admission and on the day of BSI was calculated prospectively for all patients.

Results

During the study period, among 855 consecutively admitted patients, with ICU stay longer than 48 hours, 197 patients developed BSIs due to A. baumannii (96 patients, incidence 11.23%), P. aeruginosa (44 patients, incidence 5.15%) and K. pneumoniae (57 patients, incidence 6.67%). Of these patients, 85 developed BSIs with two or more pathogens and were excluded. Thus, finally, 64 patients with A. baumannii BSI, 23 with P. aeruginosa, and 25 with K. pneumoniae were compared. Hospitalization before ICU was shorter for K. pneumoniae bacteremic patients compared with those with A. baumannii (1 vs 3 days, P = 0.028) and with those with P. aeruginosa (1 vs 6 days, P = 0.005). On ICU admission, patients with A. baumannii had a higher APACHE II score compared with those with K. pneumoniae (19.53 ± 7.6 vs 15.0 ± 5.4, respectively, P = 0.017) and lower hematocrit and hemoglobin values (29.8 ± 6.5 vs 35.4 ± 6.5, P = 0.002 and 9.9 ± 2.2 vs 11.9 ± 2.2, P = 0.001) respectively. Also on BSI day, hematocrit was lower in patients with A. baumannii and with P. aeruginosa bacteremia, compared with those with K. pneumoniae bacteremia (26.6 ± 4.5 vs 29.6 ± 4.5, P = 0.016 and 26.1 ± 3.8 vs 29.6 ± 4.5, P = 0.021). The respiratory tract was the most common source of BSIs due to A. baumannii compared with P. aeruginosa and K. pneumoniae (56.3% vs 26.1%, P = 0.013 and 56.3% vs 12.0%, P = 0.001). Mortality was higher in the presence of P. aeruginosa and A. baumannii BSIs, compared with K. pneumoniae (56.5% vs 24.0%, P = 0.021 and 48.4% vs 24.0%, P = 0.036, respectively).

Conclusion

In ICU patients, the development of BSI due to A. baumannii is associated with a higher severity of illness on admission compared with those due to P. aeruginosa and K. pneumoniae. However, P. aeruginosa BSI is associated with the higher mortality.