Prior antibiotics and risk of antibiotic-resistant community-acquired urinary tract infection: a case-control study

Background: To assess the effect of previous antibiotic use on the risk of a resistant Escherichia coli urinary tract infection (UTI), we undertook a case–control study with prospective measurement of out-comes in 10 general practices in the UK. Methods: Urinary samples from all patients with symptoms suggestive of UTIs were sought, and those with a laboratory-proven E. coli infection were interviewed and their medical records examined. Case patients were those with ampicillin- or trimethoprim-resistant infections and control patients had infec-tions that were susceptible to antibiotics, including ampicillin and trimethoprim. Results: Risk of ampicillin-resistant E. coli infection in 903 patients was associated with amoxicillin prescriptions of 7 days duration in the previous 1 month [odds ratio (OR) 5 3.91, 95 % CI 1.64–9.34] and previous 2–3 months (2.29, 1.12–4.70) before illness onset. For prescriptions <7 days duration, there was no statistically significant association. Higher doses of amoxicillin were associated with lower risk of ampicillin resistance. For trimethoprim-resistant E. coli infections, the OR was 8.44 (3.12– 22.86) for prescriptions of trimethoprim of 7 days in the previous month and 13.91 (3.32–58.31) for the previous 2–3 months. For trimethoprim prescriptions of <7 days, the OR was 4.03 (1.69–9.59) for the previous month but prescribing in earlier periods was not significantly associated with resistance