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June 03, 2021

Resistance Profiles of Oral Agents Used in the Treatment of Urinary Tract Infections as Determined by the Novel Weighted-Incidence Syndromic Combination Antibiogram (WISCA) Resistance (WISCA-R) Profiling Method, and Comparison to Previous WISCA-R Findings

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Background: The recently described weighted-incidence syndromic combination antibiogram (WISCA) displays antimicrobial susceptibilities per drug for a given syndrome, rather than per organism as in traditional antibiograms. We sought to (1) construct a WISCA resistance (R) profile (WISCA-R) per oral agent among drugs commonly used in the treatment of community urinary tract infections (UTIs), to identify oral agents with low R, and (2) to compare results to previous year WISCA-R profiles.

Methods: Isolates were identified by conventional methods from urine cultures over a 2-year period ending in December 2020 and were tested by disk diffusion or Vitek2 (bioMérieux), according to CLSI guidelines, against amoxicillin-clavulanate (AMC), ampicillin (AM), cefazolin (KZ), ciprofloxacin (CIP), fosfomycin (FOS), nitrofurantoin (FM), and trimethoprim/sulfamethoxazole (SXT). For FOS, CLSI Escherichia coli and Enterococcus faecalis breakpoints were applied to Gram-negative and -positive organisms, respectively, similar to recently published investigations. WISCA-R was constructed by multiplying the probability of weighted incidence per organism by the corresponding probability of R to the studied drug, including intrinsic R and known/imputed susceptibility per organism/drug combination, followed by the sum of obtained probabilities, to arrive at the WISCA-R rate for that drug. WISCA-R rates for 2019 vs 2020 were compared for each drug.

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