Escherichia coli belonging to the worldwide emerging epidemic clonal group O25b/ST131: risk factors and clinical implications.

OBJECTIVES: Escherichia coli belonging to clonal group ST131 has emerged as a significant contributor to infection caused by antibiotic-resistant E. coli worldwide. We investigated the risk factors for infections caused by ST131 E. coli and their clinical implications.
METHODS: One thousand and seventy-seven E. coli isolates were screened for ST131 by molecular methods. Risk factors for ST131 were investigated separately for patients with E. coli producing and not producing extended-spectrum β-lactamases (ESBLs) in the Seville area, Spain. Multivariate analysis using logistic regression was performed. Patients with infections caused by ST131 and non-ST131 isolates were prospectively followed.
RESULTS: Independent risk factors for non-ESBL-producing ST131 were female gender (OR: 1.94; 95% CI: 1.07-3.51), diabetes mellitus (OR: 2.17; 95% CI: 1.29-3.67), bedridden status (OR: 7.75; 95% CI: 0.70-85.07) and exposure to amoxicillin/clavulanate (OR: 2.07; 95% CI: 1.08-3.96) or fluoroquinolones (OR: 2.48; 95% CI: 1.41-4.34). For ESBL-producing ST131, male gender was an independent risk factor (OR: 2.20; 95% CI: 0.94-5.11), while healthcare-related acquisition and exposure to any previous antibiotic were protective (OR: 0.30; 95% CI: 0.13-0.71; and OR: 0.43; 95% CI: 0.19-1.00, respectively). Overall, the severity of sepsis, bacteraemia and mortality were similar among ST131 and non-ST131 groups. The presence of typical factors predisposing to E. coli infection was more frequent in non-ESBL-producing ST131 than in controls (76% versus 57.2%, P = 0.005).
CONCLUSIONS: Previous use of antibiotics selecting for ST131 isolates was the main modifiable risk factor for infections caused by these isolates. Our results also suggest that the clinical virulence of ST131 is not higher than that of other common E. coli causing infections.