Nosocomial gram-negative bacteremia

Objective: To review experience with hospital-acquired bacteremia due to aerobic gram-negative bacilli at the University of Alberta Hospital, episodes of nosocomial bacteremia occurring between August 1986 and June 1995 were analyzed. Methods: Since 1986, prospective surveillance has been conducted for the occurrence of hospital-acquired bloodstream infections. Cases were detected by monitoring positive blood culture results reported by the institution's clinical microbiology laboratory. Following chart review, isolates were categorized as representing a hospital-acquired infection, a community-acquired infection, or contamination, based on Centers for Disease Control and Prevention criteria. Cases were followed for 1 week to determine outcome. Results: There were 584 episodes of gram-negative bacteremia, 28.9% of all hospital-acquired bloodstream infections. The gram-negative infection rate per 1000 admissions was unchanged from 1986 to 1995, but fell as a proportion of all infections from 37.9% in 1987 to 19.8% in 1995. Escherichia coli , Klebsiella spp, Pseudomonas spp, and Enterobacter spp were the most commonly identified species, accounting for more than 85% of episodes; only the incidence of Enterobacter changed, increasing from 2 per 10,000 admissions in 1987 to 5.2 per 10,000 in 1995. The 1-week mortality rate gradually fell, from over 18% in 1987 to less than 5% in 1996 and averaged 14% for monomicrobial episodes. Pseudomonas infections were associated with significantly higher mortality (25.3%, relative risk 2.2) and Enterobacter infections with a significantly lower mortality (5.4%, relative risk 0.4). Conclusion: Over the past 9 years, the experience with the hospital-acquired bacteremia due to aerobic gram-negative bacilli at the University of Alberta Hospital revealed no significant change in the rate, causative organisms, organism-specific rates, or sources. However, as the incidence of infections due to other organisms has risen, the proportion of nosocomial bloodstream infections attribute to gram-negative organisms has gradually fallen.