Antimicrobial Resistance Trends, Resistance Mechanisms, and Antibiotic Consumption in COVID-19 Versus Non-COVID-19 Units: A Seven-Year Retrospective Cohort Study

<b>Background:</b> The COVID-19 pandemic profoundly affected healthcare delivery and antibiotic prescribing, raising concerns about increasing antimicrobial resistance. This study investigated seven-year trends in bacterial resistance, underlying resistance mechanisms, and antibiotic consumption in COVID-19 and non-COVID-19 units at a tertiary hospital in Slovakia. <b>Methods</b>: A retrospective cohort analysis (2018-2024) was conducted using clinical isolates of <i>Klebsiella</i> sp., <i>Acinetobacter</i> sp., and <i>P. aeruginosa</i>. Data on hospitalizations, resistance profiles, resistance mechanisms, and standardized antibiotic use were compared between COVID-19 and non-COVID-19 departments. <b>Results</b>: Hospitalizations markedly decreased in COVID-19 units, while pathogen occurrence-particularly of <i>Acinetobacter</i> sp.-was substantially higher compared with non-COVID-19 units. Resistance in <i>Klebsiella</i> sp. shifted from extended-spectrum beta-lactamase production to carbapenemase production. <i>Acinetobacter</i> sp. remained highly resistant, although some declines were observed in ceftazidime and gentamicin resistance. <i>P. aeruginosa</i> showed a gradual reduction in resistance, notably to piperacillin/tazobactam and imipenem. Antibiotic consumption was consistently higher in COVID-19 units, particularly for broad-spectrum beta-lactams and carbapenems, whereas fluoroquinolone use decreased over time. Clinically effective treatment options were considerably fewer in COVID-19 units, often limited to colistin. <b>Conclusions</b>: COVID-19 units experienced greater pathogen burden, higher broad-spectrum antibiotic exposure, and increased prevalence of critical resistance mechanisms. Tailored antimicrobial stewardship and infection prevention, and control are essential to reduce selective pressure and preserve last-line antibiotics.