Trimethoprim and ciprofloxacin resistance and prescribing in urinary tract infection associated with escherichia coli: a multilevel model

Individual and group level factors associated with the probability of antimicrobial resistance of uropathogenic Escherichia coli were analysed in a multilevel model. Adult patients consulting with a suspected urinary tract infection (UTI) in 22 general practices over a 9 month period supplied a urine sample for laboratory analysis. Cases were patients with a UTI associated with a resistant E. coli. Previous antimicrobial exposure and other patient characteristics were recorded from the medical files. Six hundred and thirty-three patients with an E. coli UTI and a full record for all variables were included. Of the E. coli isolates, 36 were resistant to trimethoprim and 12 to ciprofloxacin. A multilevel logistic regression model was fitted. The odds that E. coli was resistant increased with increasing number of prescriptions over the previous year for trimethoprim from 1.4 (0.82.2) for one previous prescription to 4.7 (1.912.4) for two and 6.4 (2.025.4) for three or more. For ciprofloxacin the ORs were 2.7 (1.25.6) for one and 6.5 (2.914.8) for two or more. The probability that uropathogenic E. coli was resistant showed important variation between practices and a difference of 17 for trimethoprim and 33 for ciprofloxacin was observed for an imaginary patient moving from a practice with low to a practice with high probability. This difference could not be explained by practice prescribing or practice resistance levels. Previous antimicrobial use and the practice visited affect the risk that a patient with a UTI will be diagnosed with an E. coli resistant to this agent, which was particularly important for ciprofloxacin