Abstract
<title>Abstract</title> <p> Purpose Antimicrobial resistance (AMR) in healthcare-associated infections (HAIs) represents a growing global public health threat. Composite AMR indices derived from national surveillance systems offer a standardized tool for monitoring resistance trends at the population level. This study aimed to evaluate ten-year trends in the Composite AMR Index and the Standardized Composite AMR Index of HAIs reported to the Turkish National Healthcare-Associated Infection Surveillance Network (INFLINE) between 2015 and 2024. Methods This nationwide ecological descriptive study analysed annual aggregate data from INFLINE. The Composite AMR Index was defined as the proportion of resistant isolates among six priority pathogens: <italic>Escherichia coli</italic> , <italic>Klebsiella pneumoniae</italic> , <italic>Acinetobacter baumannii</italic> , <italic>Pseudomonas aeruginosa</italic> , <italic>Staphylococcus aureus</italic> , and <italic>Enterococcus faecium/faecalis</italic> . Temporal trends were assessed using the Mann-Kendall non-parametric trend test, Spearman rank correlation, and segmented regression analysis with a pre-specified inflection point at 2021. Results During the pre-pandemic period (2015–2020), both indices remained stable between 46.0% and 50.4%, with no statistically significant trend (p = 0.45 and p = 0.57, respectively). A sharp inflection was observed in 2021, with the Composite AMR Index increasing by 14.1 percentage points in a single year (from 49.3% to 63.4%). Both indices continued to rise, reaching 67.1% and 70.6% by 2024. Overall, both indices demonstrated statistically significant increasing trends (Mann-Kendall: τ = 0.78, p = 0.002 and τ = 0.76, p = 0.003, respectively). Segmented regression confirmed a structural break at 2021, with a near-flat pre-pandemic slope (+ 0.39%/year) followed by an abrupt level shift of + 14.2 percentage points (R²=0.99). Conclusions The Composite AMR Index of HAIs in Türkiye demonstrated a stable pre-pandemic plateau followed by a sharp and sustained post-pandemic escalation, with both indices reaching approximately 65–70% by 2024. These findings suggest a structural shift in the national AMR burden associated with the COVID-19 pandemic and underscore the need for reinforced infection prevention and control measures, targeted antimicrobial stewardship, and continued national surveillance investment. </p>