Quinolone resistance in female outpatient urinary tract isolates of Escherichia coli: age-related differences.

During a 1-year period, from November 2003 to October 2004, urinary Escherichia coli isolates were collected from 20 clinical microbiology laboratories across Spain. The main objective was to assess the resistance of E. coli to the antimicrobials most commonly prescribed for community-acquired urinary tract infections depending on the patient's age. A total of 2,230 valid E. coli strains from female outpatients were isolated and sent to a single central reference laboratory for confirmation and susceptibility testing using an agar dilution method. A two-sided chi-squared test was used to assess the differences in resistance between age groups (< or =65 and >65 years). E. coli resistance was found to be more common to ampicillin (52.1%), cotrimoxazole (26%) and quinolones (18%), whereas resistance to amoxicillin-clavulanic acid, cefuroxime axetil and fosfomycin were below 3%. In women older than 65 years, resistance to ciprofloxacin reached up to 29% compared with 13% of those in the under 65 age group (p <0.001). For cotrimozaxole, rates were 32% vs. 23% (p <0.001) and for ampicillin 56% vs. 50% (p=0.02), respectively. It was concluded that fosfomycin, amoxicillin-clavulanic acid and cefuroxime axetil are the most suitable antimicrobials for empirical treatment in Spain given the high 18% and 26% resistance rates to quinolones and cotrimoxazole, respectively. Being older than 65 years of age was associated with higher resistance rates to ciprofloxacin (29%). These results should be considered when recommending empirical therapy for acute cystitis in women.