Shifts in bacterial pathogen and resistance spectra of adult respiratory tract infections before vs. after the COVID-19 pandemic: A 7-year retrospective data analysis.

OBJECTIVE

To assess the impact of the COVID-19 pandemic on the distribution and antimicrobial resistance (AMR) patterns of common bacterial pathogens isolated from respiratory specimens in adults.

METHODS

We analyzed 49,260 adult respiratory tract specimens collected between 2018 and 2024, dividing them into pre-pandemic (2018-2019), pandemic (2020-2022), and post-pandemic (2023-2024) periods. We focused on shifts in seasonal patterns, the relative abundance of five key pathogens (Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli, Staphylococcus aureus), and changes in their antimicrobial susceptibility profiles.

RESULTS

The overall pathogen positivity rate dropped from 18.60% pre-pandemic to 14.34% during the pandemic, with only a partial recovery to 15.99% afterwards. Seasonal variation was attenuated, particularly with suppressed summer rates. K. pneumoniae solidified its position as the dominant pathogen, increasing from 27.33% to 41.16% of isolates. The pandemic period saw a transient surge in A. baumannii (14.70%), which later declined. More critically, we observed a clear "rebound effect" in AMR: resistance rates to several key antimicrobials fell temporarily during the pandemic but subsequently rose to meet or exceed pre-pandemic baselines. Carbapenem resistance in A. baumannii and P. aeruginosa remained critically high (>60%).

CONCLUSION

Our data indicate that the pandemic's disruptive effects on respiratory pathogen ecology were temporary. The post-pandemic era is characterized by a consolidating dominance of K. pneumoniae, persistently high carbapenem resistance in non-fermenters, and a rebound in resistance rates for many drugs. These trends reinforce the need for continuous local surveillance and rigorous antimicrobial stewardship.