Shift of antibiotic resistance after the COVID-19 pandemic: results from the INVIFAR Network

In this study, we evaluated temporal changes in antimicrobial resistance (AMR) before, during and after the COVID-19 pandemic in Mexico.

We conducted a multicentre, retrospective surveillance study that included clinically significant isolates of Gram-positive and Gram-negative bacteria collected across Mexico between January 2019 and December 2024. Differences in antibiotic resistance among clinical specimen types and across pre-pandemic, pandemic and post-pandemic periods were assessed using Fisher's exact test and linear regression, as appropriate.

A total of 156 193 isolates were analysed. Among Enterobacterales, extended-spectrum β-lactamase-producing Escherichia coli increased from the pre-pandemic to post-pandemic period (46.5%-48.9%, P for trend = 0.005). Also, resistance to ertapenem (2.0% to 3.2%) and meropenem (1.2% to 2.7%) increased significantly (both P for trend < 0.001). In contrast, the Acinetobacter baumannii-calcoaceticus complex exhibited a significant post-pandemic decline in resistance to FEP, decreasing from 82.2% in the pre-pandemic period to 48.5% post-pandemic. Similar downward trends were observed for MEM (82.5%-65.1%) and IPM (77.2%-63.9%) (P for trend < 0.001). For Pseudomonas aeruginosa, ceftazidime resistance increased during the pandemic period (18.8%-24.4%) and declined in the post-pandemic period (20.0%). Among Gram-positive organisms, vancomycin resistance in Enterococcus faecium increased in the post-pandemic period (29.1%-43.1%, P < 0.001), and in urine isolates, a significant increase in AMP resistance was observed (76.1% in the pre-pandemic to 83.9% in the pandemic to 86.1% in the post-pandemic (P for trend = 0.029). For S. aureus, oxacillin resistance increased from 13.9% (pre-pandemic) to 19.0% (pandemic) but declined thereafter (16.5%, P < 0.001).

The COVID-19 pandemic was a major driver of AMR dynamics in Mexico, and its impact persists. While resistance rates declined for A. baumannii, rising ESBL prevalence and increasing fluoroquinolone resistance highlight persistent and emerging threats. Sustained surveillance and strengthened antimicrobial stewardship are essential to mitigate long-term post-pandemic AMR consequences.