Prevalence and predictors of trimethoprim-sulfamethoxazole resistance among uropathogenic Escherichia coli isolates in Michigan.

Resistance among uropathogenic Escherichia coli to trimethoprim-sulfamethoxazole (TMP-SMX) has increased. Risk factors for resistance and the impact on clinical failure have been poorly described. We performed a retrospective cohort study of women with acute uncomplicated cystitis seen at a university health center and at primary care clinics in southeastern Michigan from 1992 to 1999. The prevalence of TMP-SMX resistance increased from 8.1% to 15.8% (P=.01). Women who had taken TMP-SMX recently were >16 times as likely as women who had not taken antibiotics recently to be infected with an isolate resistant to this agent; those who had taken any other antibiotic were more than twice as likely to be infected with a resistant isolate. Women infected with a TMP-SMX-resistant isolate who were treated with TMP-SMX were >17 times as likely to have treatment failure. Recent antibiotic use is a risk factor for infection with a TMP-SMX-resistant isolate; patients who are infected with a TMP-SMX-resistant isolate and who are treated with this agent are at a higher risk for clinical failure.