Impact of Antibiotic Resistance and of Adequate Empirical Antibiotic Treatment in the Prognosis of Patients with Escherichia Coli Bacteraemia

Background: Escherichia coli is the most frequent Gram-negative organism causing bacteraemia. There are few data about prognostic factors of bloodstream infections due to E. coli. In particular, the consequences of antibiotic resistance and of adequate empirical antibiotic treatment on outcome remain broadly unknown.

Methods: We conducted a retrospective cohort study of patients with E. coli bacteraemia between January 1997 and June 2005 to identify any association between antibiotic resistance, adequacy of empirical antibiotic therapy and mortality.

Results: Of 663 patients with E. coli bacteraemia, 36 (5.4%) died. Patients with multidrug-resistant (MDR) E. coli bacteraemia had a significantly lower frequency of correct empirical antibiotic treatment than patients with non-MDR E. coli bacteraemia [relative risk (RR) 0.53; 95% confidence interval (CI) 0.48-0.67], and also had a significantly higher mortality (RR 3.31; 95% CI 1.72-6.36). An association between the number of antibiotics to which E. coli was resistant with adequacy of empirical antibiotic (P < 0.001) and with mortality (P < 0.001) was detected. After adjustment for other significant risk factors and confounders, the inadequacy of empirical antibiotic treatment was associated with an increased mortality (adjusted OR 2.98; 95% CI 1.25-7.11). When the adequacy of empirical treatment was excluded from the model, the presence of MDR E. coli in blood cultures was also associated with the prognosis (adjusted OR 3.11; 95% CI 1.3-7.44). In multivariate analysis, other variables associated with the outcome were age, the presence of severe sepsis or shock, Charlson index score and a non-urinary origin of the bacteraemia.

Conclusions: Adequacy of empirical antibiotic treatment is an independent risk factor for mortality in patients with E. coli bacteraemia. MDR E. coli bacteraemia had a worse prognosis due, at least in part, to a lower frequency of correct empirical treatment.