Pathogen distribution and selected phenotypic resistance trends in orthopedic-service culture-positive isolate records: a 14-year single-center surveillance study

Background Empirical antimicrobial treatment for suspected orthopedic infection is often started before culture and susceptibility results are available. Orthopedic infections may involve biofilm, retained hardware, chronic infection, repeated surgery, and prior antimicrobial exposure; these features may produce microbiological patterns that are not reflected in a hospital-wide antibiogram. We summarized long-term pathogen distribution and selected phenotypic resistance proxies among orthopedic-service culture-positive isolate records to inform local antibiogram development. Methods We conducted a single-center retrospective laboratory surveillance study including only culture-positive isolate records submitted by orthopedic services from January 2012 to December 2025. The main analysis was record-level rather than patient-level. Organism and specimen labels were standardized using the local laboratory code dictionary. Because susceptibility data were not uniformly available across the full period, selected phenotype proxies were assessed only for 2018–2025 and were reported with tested denominators, Wilson 95% confidence intervals, and exploratory trend tests. A 30-day first-isolate sensitivity analysis assessed the influence of repeat isolates, and a 100-record chart-review substudy assessed the clinical relevance and culture-informed management of recent wound/musculoskeletal-related records. Results Overall, 7,385 orthopedic-service culture-positive isolate records were analyzed; these included wound/musculoskeletal-related, blood, urinary, and respiratory specimen sources and were not restricted to confirmed orthopedic infections. Gram-negative bacteria accounted for 4,214 records (57.1%) and Gram-positive bacteria for 2,905 (39.3%). Staphylococcus aureus was the most frequent organism (1,614, 21.9%), followed by Escherichia coli (836, 11.3%) and Pseudomonas aeruginosa (831, 11.3%). After verification of historical specimen coding, wound secretion accounted for 5,504 records (74.5%). Among evaluable tested isolates in 2018–2025, the MRSA phenotype-proxy proportion changed from 51.4% to 27.0%, and the CRKP phenotypic carbapenem-resistance proxy showed a downward unadjusted trend. The CRAB proxy remained high among A. baumannii -labelled evaluable records; A. baumannii complex records were not included in that denominator. CRPA estimates were limited by small annual denominators. The 30-day first-isolate analysis preserved the MRSA and CRKP trend signals. In the recent validation subset, 96 of 100 records were clinically judged to represent infection, and culture-informed antimicrobial adjustment occurred in 64 of 91 evaluable records. Conclusions Orthopedic-service culture-positive isolate records showed a broad microbiological spectrum that varied by specimen source. These surveillance data can support development or updating of a source-stratified local orthopedic antibiogram and stewardship review. They should not be used to estimate infection incidence or, on their own, to determine empirical-treatment policy.