Seasonal trends in antimicrobial resistance of urinary Escherichia coli isolates

<h2>Abstract</h2><h3>Objectives</h3> This study aimed to examine seasonal variations in antimicrobial resistance in <i>Escherichia coli</i> urinary isolates from community and hospital settings in the Illawarra-Shoalhaven region, New South Wales, Australia, between 2007 and 2018. <h3>Methods</h3> A total of 370 461 <i>E. coli</i> urine isolates were analysed: 254 244 (68.6%) from community settings and 116 217 (31.4%) from hospital settings. Resistance patterns for amoxicillin, amoxicillin-clavulanate (Augmentin), cephalexin, norfloxacin, and trimethoprim were assessed using negative binomial regression, adjusting for temporal trends. Autumn was selected as the reference season. Adjusted incident rate ratios (IRRs) were calculated after Bonferroni correction. <h3>Results</h3> In community isolates, amoxicillin resistance was higher in spring (IRR: 1.09, p <0.001) and in winter (IRR: 1.08, p <0.001). Trimethoprim resistance was also slightly higher in spring (IRR: 1.08, p 0.01). No significant seasonal variation was observed in antimicrobial resistance rates for hospital isolates. Additionally, amoxicillin-clavulanate, cephalexin, and norfloxacin did not demonstrate seasonal trends in either community or hospital settings. <h3>Conclusions</h3> Seasonal variations in community <i>E. coli</i> resistance to amoxicillin and trimethoprim were identified, emphasizing the need for targeted antimicrobial stewardship in primary care. These findings suggest that resistance rates may be modifiable and underscore the need for further investigation into the relationship between seasonal antibiotic prescribing patterns and resistance trends.