Magnitude of bacteraemia predicts one-year mortality

Objectives: All hospitals in our region use the BacT/Alert® blood culture (BC) system with a 3-bottle BC set for adults. We hypothesized that the magnitude of bacteremia (i.e., number of positive bottles in the initial BC set) predicted one-year mortality. Methods In a population-based study we analyzed all patients with monomicrobial bacteremia in North Jutland County, Denmark, 1996-2004. Data from the County Bacteremia Registry were linked to the Hospital Discharge Registry (comorbidity) and the Danish Civil Registration System (vital status, including date of emigration or death). Patients with a BC index of 1 (i.e., one positive bottle) were chosen as the reference group. We computed Kaplan-Meier curves and performed Cox regression analyses to estimate mortality rate ratios (MRRs) with 95 % confidence intervals [CIs] 30 and 365 days after the initial BC sampling date, first in crude analyses, second in analyses adjusted for age, comorbidity, acquisition of infection (community, nosocomial, orhealth-care related), and incident or recurrent episode. In addition we stratified the analyses on acquisition of infection and pathogen group. Results A total of 6955 patients had 8152 episodes of monomicrobial bacteremia, among which one-year follow-up was possible for 8108 (99.5 %). Of these, 2539, 1511, and 4058 episodes had a BC index of 1, 2, and 3, respectively. In crude analyses, 30-day MRRs were 0.98 [0.85-1.14] and 1.20 [1.07-1.34] for BC indices 2 and 3, respectively, and similar MRRs were found after 1 year (0.99 [0.89-1.09] and 1.12 [1.04-1.21]). All estimates remained unchanged in the adjusted analyses. Results for community-acquired and health-care related bacteremia episodes were consistent with the non-stratified results, whereas all MRRs for nosocomial infections were close to 1. A BC index of 3 had the strongest long-term prognostic impact in pneumococcal bacteremia (n=855) (adjusted MRR 1.60 [1.09-2.34]). In patients with community-acquired or health-care related bacteremia, high magnitude of bacteremia (i.e., a BC index of 3) predicted increased  30-day as well as 365-day mortality.