Antimicrobial resistance trends in common urinary pathogens

Urinary tract infections (UTIs) are the second most common infectious presentations in community practice. Over 90% of UTIs are due to a single species. Escherichia coli alone accounts for 80% to 90% of UTIs. In young, healthy women, Staphylococcus saprophyticus accounts for approximately 5% to 15% of cases of uncomplicated cystitis, but is rarely associated with pyelonephritis or complicated infections. Other gram-negative species comprise the majority of the remaining causes of UTIs. Because initial antimicrobial therapy for UTIs is generally empiric, it is important to account for local susceptibility trends when selecting an antimicrobial agent. In Canada, resistance among community-acquired (as opposed to nosocomial or hospital-acquired) isolates of E. coli varies depending on the antimicrobial agent being tested. Ampicillin has the lowest activity against community-acquired E.coli isolates, with resistance rates ranging from 23% to 41%. Trimethoprim-sulphamethoxazole (TMP-SMX) resistance rates range from 8.4% to 19.2%, while the resistance to the fluoroquinolone ciprofloxacin has remained at 0% to 1.8% since its introduction over 10 years ago. Current studies suggest that there are no regional differences in resistance rates among community-acquired urinary tract pathogens across Canada.