Objective: Surgical site infection (SSI) after spinal surgery has substantial clinical and economic impact and remains difficult to prevent completely despite preventive strategies, including perioperative antibiotic prophylaxis. We aimed to clarify the SSI rate and trends in causative pathogens over 15 years in our department.

Methods: We reviewed 10,432 spinal surgeries performed at our institution between 2010 and 2024. SSI was defined as infection requiring operative irrigation and debridement in the operating room. We analyzed SSI rates according to implant use,

causative organisms, patient characteristics (e.g., age and diabetes), surgical factors (operative time and blood loss), and the interval from surgery to SSI recognition, with statistical analyses. For pathogen- based comparisons, cases were categorized into three common groups: MSSA+MSSE, MRSA+MRSE, and

P. acnes.

Results: The overall SSI rate was 0.96% (100/10,432). SSI occurred in 0.56% (33/5,857) of surgeries without implants and 1.46% (67/4,575) with implants, indicating a significantly higher rate in the implant group. Pathogens were heterogeneous; however, P. acnes and MRSA were detected significantly more often in implant-associated cases. The most frequent groups were MSSA+MSSE (n=34), MRSA+MRSE (n=19), and C. acnes (n=13). There were no significant between-group differences in age, implant use, operative time, or blood loss; however, time to SSI recognition differed significantly, with the P. acnes group showing the latest presentation.

Discussion: Implant use was a risk factor for SSI, and

P. acnes was characteristic of delayed-onset infection. Longer postoperative follow-up and refinement of antimicrobial protocols may be required.

Conclusion: SSI occurred in approximately 1% of spinal surgeries, and implant-associated SSI and delayed-onset P. acnes infection remain important clinical issues.