Co-resistance Among Escherichia coli and Klebsiella pneumoniae Urine Isolates from Female Outpatients with Presumed UTI: A Retrospective US Cohort Study

Urinary tract infections (UTIs) caused by antimicrobial-resistant Enterobacterales are a global health threat. There are limited surveillance data available to characterize the prevalence of antimicrobial resistance among outpatients in the United States (US).

This retrospective cohort (database) study investigated co-resistance among Escherichia coli and Klebsiella pneumoniae urinary isolates from US female outpatients aged ≥ 12 years with presumed uncomplicated UTI (uUTI), ≥ 3 months of data (2011–2019), and antimicrobial susceptibility testing results. Eligible isolates were the first urinary E. coli or K. pneumoniae isolate per patient collected within 30 days; classified as not susceptible (NS) if antimicrobial susceptibility testing results were intermediate or resistant to each antibiotic tested. Four resistance phenotypes were identified: NS to fluoroquinolones (FQ), trimethoprim/sulfamethoxazole (SXT), nitrofurantoin (NTF), and extended-spectrum β-lactamase+/third-generation cephalosporin (ESBL+/3GC NS). Co-resistance phenotypes included all possible combinations of resistance to ≥ 2 drug classes.

Of 1,513,882 E. coli isolates and 250,719 K. pneumoniae isolates, 856,918 and 187,459 isolates with ≥ 1 resistance phenotype were included in the analysis, respectively. The most common resistance phenotypes were SXT NS for the E. coli isolates (44.8%) and NTF NS for the K. pneumoniae isolates (75.5%), while ESBL+/3GC NS comprised 11.2 and 5.9%, respectively. Among ESBL+/3GC NS E. coli isolates, 72.4, 56.7, and 46.6% were co-resistant to FQ, SXT, and FQ + SXT, respectively. For ESBL+/3GC NS K. pneumoniae isolates, 65.7 and 45.7% were co-resistant to SXT and FQ + SXT.

Both species exhibited high rates of co-resistance, emphasizing the need to raise awareness of co-resistance and of the unmet need for effective treatment options for uUTI.