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

https://doi.org/10.1016/j.ijantimicag.2005.08.003Get rights and content

Abstract

The goal of the North American Urinary Tract Infection Collaborative Alliance (NAUTICA) study was to determine antibiotic susceptibility to commonly used agents for urinary tract infections against outpatient urinary isolates obtained in various geographic regions in the USA and Canada. Forty-one medical centres (30 from the USA and 11 from Canada) participated, with each centre submitting up to 50 consecutive outpatient midstream urine isolates. Isolates were identified to species level by the standard protocol of each laboratory. Susceptibility testing was determined using the National Committee for Clinical Laboratory Standards (NCCLS) microdilution method. Resistance breakpoints used were those published by the NCCLS, including: 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). Of the 1990 isolates collected, 75.1% (1494) were collected from the USA and 24.9% (496) were collected from Canada. The mean age of the patients was 48.3 years (range 1 month to 99 years), and 79.5% and 20.5% of isolates were obtained from women and men, respectively. The most common organisms were Escherichia coli (57.5%), Klebsiella pneumoniae (12.4%), Enterococcus spp. (6.6%), Proteus mirabilis (5.4%), Pseudomonas aeruginosa (2.9%), Citrobacter spp. (2.7%), Staphylococcus aureus (2.2%), Enterobacter cloacae (1.9%), coagulase-negative staphylococci (1.3%), Staphylococcus saprophyticus (1.2%), Klebsiella spp. (1.2%), Enterobacter aerogenes (1.1%) and Streptococcus agalactiae (1.0%). Among all 1990 isolates, 45.9% were resistant to ampicillin, 20.4% to SMX/TMP, 14.3% to nitrofurantoin, 9.7% to ciprofloxacin and 8.1% to levofloxacin. Fluoroquinolone resistance was highest in patients ≥65 years of age. For the 1142 E. coli isolates, resistance rates were: ampicillin 37.7%, SMX/TMP 21.3%, ciprofloxacin 5.5%, levofloxacin 5.1% and nitrofurantoin 1.1%. For all 1990 isolates and for the 1142 E. coli only, resistance rates were significantly higher in US compared with Canadian medical centres. This study reports higher rates of antibiotic resistance in US versus Canadian outpatient urinary isolates and demonstrates the continuing evolution of resistance to antimicrobial agents.

Introduction

Urinary tract infections (UTIs) including cystitis and pyelonephritis are common both in community and hospital settings [1], [2], [3], [4], [5], [6]. The bacterial aetiology of UTIs is well established, with Escherichia coli being the predominant pathogen [2], [7], [8], [9], [10], [11], although other organisms gain greater importance in patients with complicated UTI [12], [13]. The guidelines of the Infectious Diseases Society of America recommend that uncomplicated UTIs should be treated empirically with sulphamethoxazole/trimethoprim (SMX/TMP) unless resistance rates of community-acquired E. coli to this agent exceed 10–20%, in which case a fluoroquinolone should be used [14]. Resistance of E. coli and other Enterobacteriaceae, however, has continued to evolve, with decreasing susceptibility to first-line agents such as ampicillin, nitrofurantoin, SMX/TMP and, more recently, the fluoroquinolones such as ciprofloxacin and levofloxacin [7], [8], [9], [10], [11], [12], [13], [15], [16], [17], [18], [19], [20]. As antibiotic therapy for uncomplicated UTIs is initiated empirically, antibiotic resistance profiles at the local, national and international levels must be known.

The goal of the North American Urinary Tract Infection Collaborative Alliance (NAUTICA) study was to determine antibiotic susceptibility to commonly used first-line antibiotics in outpatient urinary isolates obtained from various geographic regions in the USA and Canada.

Section snippets

Isolate collection

NAUTICA is a UTI surveillance study involving 41 medical centres (30 from the USA and 11 from Canada). The majority of geographic regions of both the USA and Canada were represented (Appendix A Participating US investigators/sites, Appendix B Participating Canadian investigators/sites). From April 2003 to June 2004 inclusive, each centre submitted up to 50 consecutive outpatient midstream urine isolates. All isolates were deemed significant urinary tract pathogens by individual laboratory

Patient demographics

The demographics of the patients from whom the outpatient urinary isolates were obtained are described in Table 1. The mean age was 48.3 years (range 1 month to 99 years). Women in the 15–50-year-old group represented 39.3% of the isolates, whilst 34.1% of isolates were obtained from men and women ≥65 years of age. Isolates obtained from the USA represented 75.1% of all strains and Canadian strains represented 24.9% of all isolates collected.

Bacteriology of outpatient urinary isolates

The bacteriology of the 1990 outpatient urinary

Discussion

NAUTICA is an ongoing North American surveillance study assessing antibiotic resistance rates to commonly used agents in outpatient urinary tract pathogens. Although data were obtained from children ≤14 years of age as well as post-menopausal women 51–64 years of age, the majority of isolates obtained in this study were from pre-menopausal women (38.3% of all isolates) and elderly (≥65 years) females (20.1% of all isolates) (Table 1). In addition, the urinary isolates came primarily from the

Acknowledgments

This study was supported in part by the University of Manitoba, Procter & Gamble Inc. and Ortho-McNeil. Dr Ayman Noreddin is supported by an ACCP/Aventis Postdoctoral Fellowship. The authors thank M. Tarka for expert secretarial support.

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