Global Epidemiology of Multidrug-Resistant Lower Respiratory Infections in Adults ≥55 years: Trends (1990–2021) and Projections to 2050

Background: The global aging population has amplified the public health burden of multidrug-resistant (MDR) lower respiratory infections (LRIs), particularly among adults aged ≥55 years. Acinetobacter baumannii (AB), Pseudomonas aeruginosa (PA), and Klebsiella pneumoniae (KP) (collectively KAP) are leading MDR Gram-negative pathogens causing LRIs in this demographic, yet comprehensive global epidemiological data on KAP-related LRIs in adults ≥55 years remain scarce. Methods : Using data from the Global Burden of Disease (GBD) 2021, we analyzed trends in disability-adjusted life years (DALYs) and age-standardized rates (ASR) of KAP-related LRIs in adults ≥55 years across 204 countries/territories from 1990 to 2021. Estimated annual percentage changes (EAPC) were calculated to assess temporal trends, with stratification by age, sex, and Socio-demographic Index (SDI). Future burdens (to 2050) were projected using dual models: Bayesian Age-Period-Cohort (BAPC) and Autoregressive Integrated Moving Average (ARIMA). Result： Globally, AB- and KP-related DALY ASRs declined significantly (EAPC: AB=-2.40, 95%CI:-2.48–-2.32; KP=-0.82, 95%CI:-0.89–-0.74) from 1990 to 2021, while PA-related ASR increased (EAPC=0.33, 95%CI:0.24–0.43) and was projected to stabilize post-2025. Burden was highest in adults ≥95 years (e.g., PA-related ASR 26-fold higher than 55–59 years) and males (2021: AB ASR males=72.97 vs. females=56.11 per 100,000). Low-middle SDI regions bore the heaviest burden, whereas high-SDI regions showed the steepest declines (AB EAPC=-3.81, 95%CI: -4.02 to -3.59). Dual models confirmed AB- and KP-related burdens would continue decreasing by 2050, but PA-related burden would persist. Conclusion: KAP-related LRIs in adults ≥55 years exhibit pathogen-specific, demographic, and geographic disparities, with PA emerging as a persistent threat. Targeted interventions are needed to mitigate burden and promote healthy aging globally.