Individual and community predictors of urinary ceftriaxone-resistant Escherichia coli isolates, Victoria, Australia

Background: Ceftriaxone-resistant Enterobacteriaceae are priority pathogens of critical importance. Escherichia coli is the most commonly isolated Enterobacteriaceae. There are few data regarding non-invasive ceftriaxone-resistant E. coli (CR-EC) isolates in the Australian community. We aimed to describe the prevalence, phenotype, geographic variation, and sociodemographic predictors of ceftriaxone-resistance among E. coli isolates recovered from urine specimens. Methods: In August 2017, we prospectively analysed E. coli isolates recovered from urine specimens submitted to Dorevitch Pathology (Victoria, Australia), a laboratory that services patients in the community and hospitals. In addition to patient-level predictors of ceftriaxone resistance, we mapped patient postcodes to community-level indicators including Index of Relative Socioeconomic Deprivation, remoteness, and proportion of residents born overseas. We used Poisson regression with log link and robust standard errors to quantify the association between ceftriaxone resistance and patient- and community-level factors. Results: We included 6732 non-duplicate E. coli isolates. Most (89.2%, 6008/6732) were obtained from female patients. Median age was 56years (IQR, 32-74). Most patients (90.5%, 5789/6732) were neither referred from a hospital nor residing in a residential aged care facility (RACF). Among the 6732 isolates, 5.7% (382) were CR-EC, ranging from 3.5% (44/1268) in inner regional areas to 6.3% (330/5267) in major cities. Extended spectrum beta-lactamase (ESBL) -production was the most common mechanism for ceftriaxone resistance (89%, 341/382). Nitrofurantoin was the most active oral agent against CR-EC. Eight CR-EC isolates (2.4%) were susceptible only to amikacin, meropenem and nitrofurantoin. None were resistant to meropenem. On multivariable analysis, ceftriaxone resistance was associated with age, residence in a RACF (adjusted relative risk [aRR] 2.94, 95% confidence interval [CI] 2.10-4.13), specimen referral from hospital (aRR 2.05, 95% CI 1.45-2.9), and the proportion of residents born in North Africa and the Middle East (aRR 1.30 for each 5% absolute increase, 95% CI 1.09-1.54), South-East Asia (aRR 1.14, 95% CI 1.02-1.27), and Southern and Central Asia (aRR 1.16, 95% CI 1.04-1.28). Conclusions: These results provide insights into sociodemographic variation in CR-EC in the community. A better understanding of this variation may inform empiric treatment guidelines and strategies to reduce community dissemination of CR-EC.