Five years of nosocomial Gram-negative bacteremia in a general systems intensive care unit

Objectives

Nosocomial Gram-negative bacteremia in the critically ill is associated with significant morbidity and mortality. This study provides epidemiological and antimicrobial susceptibility data for nosocomial Gram-negative bacteremia in a general systems ICU over a 5-year period.

Methods

Positive blood cultures from 1 January 1999 to 31 December 2003 were reviewed for microbial etiology and susceptibilities. Patient charts were reviewed to determine the source of infection, time from admission to bacteremia, causative organisms, antimicrobial susceptibilities, choice of empiric antibiotic therapy and outcome.

Results

There were 1632 admissions with 45 nosocomial Gram-negative bacteremias in 44 patients. Infection rates of 28.2/1000 admissions and 12.1/10 000 patient-days remained stable over 5 years. The mean patient age was 55.3 years (range 17–86 years); 27.3% of patients were female, and 72.8% were male. The majority (95.6%) of bloodstream infections were monomicrobial, with only one episode of polymicrobial bacteremia. Common admitting diagnoses included respiratory failure, solid organ transplant, post-surgery, and multi-trauma. Seven bacterial species were identified; Pseudomonas aeruginosa and Enterobacter spp. were most common. Sources of bacteremia included pneumonia (48.9%), followed by central venous catheterization (22.2%). The mean time from admission to hospital to development of bacteremia was 32.9 days (95% confidence interval [CI] 0–100.9), and time from admission to the ICU was slightly less at 26.0 days (95% CI 0–90.1). Antimicrobial susceptibilities were highest for imipenem, gentamicin, tobramycin, ceftazidime, and piperacillin/tazobactam. Ciprofloxacin susceptibility was inferior to imipenem, gentamicin, and tobramycin (P < 0.05). Empiric coverage with an agent to which the microorganism was ultimately susceptible was 89.2%. The mortality rate was 53.3% in the ICU, and 60.0% for overall hospitalization, compared with an overall mortality rate of 11.7% for the year 2004 in our ICU patients. The average length of the ICU stay was 50.5 (95% CI 0–150.1) days compared with 6.13 (95% CI 4.29–7.97) days for all-comers.

Conclusions

Nosocomial Gram-negative bacteremia is associated with marked morbidity and mortality in critically ill patients. Significant resistance to ciprofloxacin was demonstrated. Empiric treatment regimens should be based on unit-specific data.