Background: The burden of antimicrobial resistance is high in solid organ transplant (SOT) recipients. Among Swiss SOT recipients, we assessed temporal trends of ESBL-producing Enterobacterales (ESBL-E), identified risk factors for ESBL-E, and assessed the impact of resistance on patient outcome.

Methods: Data from the Swiss Transplant Cohort Study (STCS), a nationwide prospective cohort of SOT-recipients, were analysed. Temporal trends were described for ESBL-detection among Escherichia coli and non-Escherichia coli. In a nested case-control study, cases with ESBL-E infection were 1:1 matched (by time since transplantation, organ transplant, pathogen) to controls infected with non-ESBL-E. Factors associated with resistance and with unfavourable 30-day outcome (death, infection relapse, graft loss) were assessed.

Results: From 2012 to 2018, we identified 1'212 infection episodes caused by Enterobacterales in 1'074 patients, thereof 11.4% (138/1'212) caused by ESBL-E. The proportion of ESBL-production among Escherichia coli remained stable over time (p = 0.93) but increased for non-E. coli (p = 0.02) Enterobacterales. In the case-control study (n = 102), antibiotic pre-treatment was independently associated with ESBL-production (aOR = 2.6, 95%-CI: 1.0-6.8, p = 0.046). Unfavourable outcome occurred in 24/51 (47%) cases and 9/51 (18%) controls (p = 0.003). Appropriate empiric antibiotic therapy was the only modifiable factor associated with unfavourable outcome.

Conclusions: In Swiss SOT-recipients, proportion of infections with ESBL-producing non-E. coli Enterobacterales increased in recent years. Antibiotic pre-treatment represents a risk factor for ESBL-E. Improving appropriateness of empiric antibiotic treatment might be an important measure to reduce unfavourable outcome, which was observed in almost half of SOT-recipients with ESBL-E infections.