Seasonal Variation in Antimicrobial Resistance Rates of Community-Acquired Escherichia coli Bloodstream Isolates

Abstract Seasonal variation in antimicrobial consumption in the community has been demonstrated, with lowest utilization rates during summer months. This retrospective cohort study aims to examine seasonality in antimicrobial resistance rates of community-acquired Escherichia coli bloodstream isolates. E. coli bloodstream isolates from January 1, 2010 to December 31, 2015 were identified through Palmetto Health central microbiology laboratory in Richland County, SC, USA. Multivariate logistic regression was used to examine seasonal variation in antimicrobial resistance and Poisson regression to evaluate association between proportion of multi-drug resistant (MDR) isolates and bi-monthly ambulatory antimicrobial prescription rates. Among 339 unique patients with community-acquired E. coli bloodstream infections, median age was 65 years and 205 (60%) were women. Antimicrobial resistance rates were lower during summer (June-September) than rest of the year for amoxicillin-clavulanic acid (17% vs. 29%, adjusted odds ratio [aOR] 0.53, 95% confidence intervals [CI]: 0.30-0.92, p=0.02], cefazolin (6% vs. 19%, aOR 0.26, CI: 0.10-0.58, p E. coli declined from 31-36% during peak of antimicrobial prescription to 11-14% in summer months; a 6.8% decline per each interval decrease in antimicrobial prescription rates of 10/100 person-years (p=0.01). There is significant seasonal variation in antimicrobial resistance rates of E. coli bloodstream isolates to four agents from frequently utilized antimicrobial classes in community. Examination of seasonal variation in the most dominant serotypes of community-acquired E. coli bloodstream isolates in future investigations will be valuable.