Antibiotic resistance in Escherichia coli outpatient urinary isolates: final results from the North American Urinary Tract Infection Collaborative Alliance (NAUTICA)

The North American Urinary Tract Infection Collaborative Alliance (NAUTICA) study determined the antibiotic susceptibility to commonly used agents for urinary tract infections of outpatient Escherichia coli urinary isolates obtained from various geographic regions in the USA and Canada. NAUTICA involved 40 medical centres (30 from the USA and 10 from Canada). From April 2003 to June 2004 inclusive, each centre submitted up to 50 consecutive outpatient midstream urine isolates. All isolates were identified to species level by each laboratory's existing protocol. Susceptibility testing was determined using the Clinical and Laboratory Standards Institute (CLSI) microdilution method. Ampicillin (resistant ≥32 μg/mL), sulphamethoxazole/trimethoprim (SMX/TMP) (resistant ≥4 μg/mL), nitrofurantoin (resistant ≥128 μg/mL), ciprofloxacin (resistant ≥4 μg/mL) and levofloxacin (resistant ≥8 μg/mL) resistance breakpoints used were those published by the CLSI. Of the 1142 E. coli collected, 75.5% (862) were collected from the USA and 280 (24.5%) were from Canada. Patient demographics revealed a mean age of 48.1 years (range, 2 months to 99 years), with female patients representing 79.4% of patients and males representing 20.6%. Overall, resistance to ampicillin was 37.7%, followed by SMX/TMP (21.3%), nitrofurantoin (1.1%), ciprofloxacin (5.5%) and levofloxacin (5.1%). Resistance rates for all antimicrobials were higher in US medical centres compared with Canadian centres (P < 0.05). Fluoroquinolone resistance was highest in patients ≥65 years of age (P < 0.05). Resistance rates demonstrated considerable geographic variability both in the USA and Canada. This study reports higher rates of antibiotic resistance in US versus Canadian outpatient urinary isolates of E. coli and demonstrates the continuing evolution of resistance to antimicrobial agents.