No significant excess mortality in ICU patients with nosocomial Escherichia coli bacteremia

Purpose and methods

The objective of this retrospective matched cohort study was to evaluate the excess mortality in critically ill patients with E. coli bacteremia after accurate adjustment for severity of illness. ICU patients with nosocomial E. coli bacteremia were matched (1:2 ratio) on the basis of the APACHE II system: equal APACHE II score (± 2 points) and diagnostic category. Since expected mortality can be calculated from this severity of disease scoring system, this matching procedure results in an equal expected inhospital mortality rate for patients with (cases: n = 64) and without E. coli bacteremia (controls: n = 128).

Results

The average APACHE II score (± SD) for cases and controls was 25 ± 9.2 (median: 23). This represented an expected inhospital mortality rate of approximately 47 ± 27.4% (median 44%) in both groups. ICU patients with E. coli bacteremia had more hemodynamic instability (75% vs 56%; P = 0.009), they were mechanically ventilated for a more extended period (median 14 days vs 3 days; P = 0.001), and had a longer ICU stay (median 17 days vs 5 days; P < 0.001). No statistically significant differences between cases and controls were noted in incidence of acute respiratory failure (respectively 81% vs 77%; P = 0.534), acute renal replacement therapy (respectively 27% vs 18%; P = 0.167) and age (respectively median 57 years vs 58 years; P = 0.260). Inhospital mortality rates for cases and controls were not different, respectively 43.8% and 43.0% (P = 0.918). Thus, the excess mortality was 0.8% (95% CI: -14.1 to 15.7%). The absence of a significant excess mortality in the cases might be due to the high rate of appropriate antibiotic therapy (93%) and the overall short delay in the start of treatment (0.6 ± 1.0 days).

Conclusion

After careful adjustment for severity of underlying disease and acute illness, no significant excess mortality was found between ICU patients with and without E. coli bacteremia. These results must be seen in the light of fast initiation of appropriate therapy.