Trimethoprim-sulfamethoxazole resistance among urinary coliform isolates

A large majority of urinary tract infections are caused by coliform organisms. Trimethoprim-sulfamethoxazole (TMP-SMX) resistance among uropathogens is increasing in many areas. The objective of this study was to determine risk factors for TMP-SMX-resistant coliforms in patients with urinary tract infections.

Retrospective case-control study.

Emergency department of a tertiary care university hospital.

We studied 448 emergency department patients aged 14 years or older with a urinary tract infection caused by a coliform organism. Cases consisted of all patients with a culture-documented urinary tract infection caused by a TMP-SMX-resistant coliform, while control patients were those with a TMP-SMX-sensitive organism.

A univariate analysis of clinical variables associated with TMP-SMX resistance was performed. Multiple logistic regression was performed to determine independent predictors of TMP-SMX resistance. Resistance to TMP-SMX was seen in 15% of isolates. Numerous variables were associated with TMP-SMX resistance on the univariate screen. Independent predictors of resistance were diabetes (odds ratio [OR] 3.1; 95% confidence interval [CI] 1.2, 8.4), recent hospitalization (OR 2.5; 95% CI 1.1, 5.7), current use of antibiotics (OR 4.5; 95% CI 2.0, 10.2), and recent use of TMP-SMX (OR 5.1; 95% CI 2.2, 11.5). When those with recent hospitalization were excluded from analysis, independent predictors were current use of any antibiotic (OR 3.5; 95% CI 1.4, 8. 4) and recent use of TMP-SMX (OR 5.9; 95% CI 2.4, 14.3).

Coliforms resistant to TMP-SMX are common in our emergency department. Diabetes, recent hospitalization, and the use of antibiotics, particularly the use of TMP-SMX, are independent risk factors for TMP-SMX resistance. Clinicians should consider these findings when deciding on antimicrobial therapy for patients with urinary tract infections.