Urinary Tract Infections Caused by ESBL-producing Enterobacteria

The aim of this study was to compare the etiologic agents, the antimicrobial resistance rates, and the risk factors associated with a HA-UTI and CA-UTI among complicated and uncomplicated UTI patients in a tertiary-care hospital in Mexico.

This study was performed according to the principles expressed in the Declaration of Helsinki with the approval of the Local Ethics Committee of the School of Medicine of the Universidad Autónoma de Nuevo León (UR14-004).

All patients with a UTI and a positive urine culture (> 100,000 UFC/mL) from March to October 2015 were included. The study was carried out at the Hospital Universitario "Dr. José Eleuterio González" hospital, a tertiary-care teaching hospital in Monterrey, Mexico. This hospital has 500 beds, serves a population of approximately 5 million people, and has an average of 250,000 medical consultations and 22,000 hospitalizations annually.

A UTI was defined as the presence of symptoms related to the urinary tract, pyuria (≥10 leucocytes per high-power field) and a positive urine culture (≥105 CFU/mL) of one uropathogen according to the guidelines of the Infectious Diseases Society of America (IDSA) and the European Association of Urology (EAU). Patients with urine cultures with significative counts of two or more bacterial species were excluded.

Patients' charts were reviewed for clinical and demographic characteristics. The classification of UTIs as either complicated or uncomplicated, and hospital-acquired or community-acquired, was based on the IDSA and EAU criteria. Cases which could not be classified due to insufficient clinical information were excluded.

Urine cultures were performed according to standard protocols. Species identification of all isolates was performed using MALDI-TOF mass spectrometry (Microflex, Bruker Daltonics, Billerica, MA). The drug resistance profile of all E. coli isolates was determined using the broth microdilution method for gentamicin, amoxicillin-clavulanic acid, aztreonam, ceftriaxone, ertapenem, ciprofloxacin, levofloxacin, nitrofurantoin, trimethoprim/sulfamethoxazole, and colistin; except fosfomycin, in which the agar dilution method was used. The results were interpreted according to the Clinical and Laboratory Standards Institute (CLSI) criteria.

Multidrug resistance (MDR) was defined as non-susceptibility to at least one agent in three or more antimicrobial categories. All isolates with resistance to at least one third-generation cephalosporin were evaluated for production of ESBL in E. coli using the double-disc test according to the CLSI.

Categorical variables were expressed as frequencies and percentages. Numerical variables were expressed as a mean and standard deviation. Clinical and demographic characteristics were analyzed using the χ2 test for categorical variables and the t-test (or Mann-Whitney test in the absence of normal distribution) for continuous variables. Statistical significance was set at p <0.05. Statistical analysis was performed with the SPSS software version 20.0 (IBM Corp, Armonk, NY).