Cephalosporin and fluoroquinolone combinations are highly associated with CTX-M β-lactamase-producing Escherichia coli: a case–control study in a French teaching hospital

The aim of this study was to investigate the risk factors associated with CTX-M-producing Escherichia coli strains isolated from infected or colonized patients. From 191 clinical samples, a case–control study was designed. From January 2005 to December 2007, 98 hospitalized patients infected or colonized with CTX-M-producing E. coli were included in the study. They were matched 1 : 1 with controls that had a non-CTX-M-producing E. coli infection on the basis of the site of sample, the unit of hospitalization and the time at risk. The rate of CTX-M-producing E. coli among those producing extended spectrum β-lactamases was always ≥90% from 2005 to 2008. All strains were susceptible to carbapenems. However, we observed a high rate of co-resistance to ciprofloxacin (61%), sulphonamides (86%) and gentamicin (34%). Significant risk factors identified by multivariate analysis were recurrent infections (OR = 2.93), presence of artificial nutrition (OR = 3.99), and recent exposure to quinolones (OR = 4.39), third- or fourth-generation cephalosporin (OR = 3.49) and the combination of both antibiotic classes (OR = 5.50). This report highlights the dramatic increase of CTX-M-producing E. coli and the need for changes in the use of antimicrobial drugs and in infection control measures to manage this major health concern.