Factors associated with antibiotic resistance in coliform organisms from community urinary tract infection in Wales

Routine susceptibility data for urinary coliform isolates from community practice were analysed in comparison with dispensed antibiotic prescriptions for all conditions and social deprivation data for Bro Taf and North Wales Health Authorities for financial years 1996-1998. Prescribing rates and resistance rates varied widely between practices. Among isolates from practices with high usage of an antibiotic, rates of resistance to that antibiotic tended to be high, and usage correlated significantly with resistance between practice population units. Cross-correlations were found between usage of one antibiotic and resistance to another, particularly for trimethoprim and ampicillin. Usage, particularly of trimethoprim, was associated with multi-resistance to up to four antibiotics. Resistance was more frequent in isolates from males, children and the elderly. Ampicillin resistance correlated with social deprivation. Analyses including or excluding potential repeat isolates yielded closely similar results. Indices reflecting sampling behaviour (laboratory coliform positivity rates, positivity per 1000 registered patients, specimens submitted per 1000 registered patients) varied widely between surgeries, suggesting lack of consensus on urine sampling policies. These indices showed only weak correlations with usage or resistance. Associations between resistance and usage were compared for isolates from two patient subsets that were likely to differ in their proportions of non-Escherichia coli isolates: female patients aged 16-55 years; and males, children and patients aged >55 years. The latter showed higher base levels of resistance, but the associations of resistance with usage were statistically indistinguishable for the two populations. The results suggest that usage of antibiotics in a practice population may affect the rate of urinary infection caused by resistant coliform organisms in that population.