Development of a Urinary-Specific Antibiogram for Gram-Negative Urinary Isolates: Impact of Patient Factors on Susceptibility

Background: Antimicrobial resistance has a significant impact on patient morbidity and mortality.  Traditional antibiograms are used to guide clinicians in selecting appropriate empiric antimicrobials however, they lack data on syndrome or disease specific susceptibility, isolate location, polymicrobial infections, and patient-specific factors. The aim of this study is to develop a urinary-specific antibiogram and to determine the impact of patient specific factors on antimicrobial susceptibility for patients who present to Advocate Lutheran General Hospital (ALGH) with urinary tract infections (UTIs).

Methods: The urinary-specific antibiogram was developed utilizing laboratory culture and susceptibility data of urinary isolates obtained at ALGH between January 1, 2012 and December 31, 2012.  The antibiogram is specific to four common gram negative urinary pathogens: Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis, and Pseudomonas aeruginosa. The susceptibilities in the urinary-specific antibiogram were compared to susceptibilities in the standard antibiogram. The four urinary isolates were then stratified by patient factors to determine the impact on antimicrobial susceptibility: prior residence, age, systemic antimicrobial use ≤ 30 days, and hospitalization ≤ 30 days. 

Results: There were a total of 2,238 urinary isolate encounters from January 1 to December 31, 2012.  Antibimicrobial susceptibility was significantly greater in the urinary antibiogram and there was a significant increase in the prevalence of urinary ESBL producing isolates compared to the standard antibiogram.  Further impact on antimicrobial susceptibility was reported when the four urinary isolates were stratified by patient factors.  Healthcare facility had the greatest impact on antimicrobial susceptibility and fluoroquinolone susceptibility significantly decreased when stratified by all patient factors for each of the four urinary isolates (p < 0.05).        

Conclusion: Utilizing a syndromic antibiogram and incorporating patient-specific factors into susceptibility data may be more useful in aiding clinicians to select more appropriate empiric therapy for a specific indication.