Science, Medicine, and the Anesthesiologist

Surgical site infection affects 1 in 30 procedures and represents the costliest complication of surgery. However, it is elusive whether surgical site infections are caused by exogenous sources from nosocomial reservoirs or by endogenous reservoirs of colonizing microbiota carried by the patient. With the use of instrumented spine surgery as a model of clean skin incision, preoperative microbiomes from different anatomic sites and microbiomes from postoperative surgical site infections were determined in a cohort of 204 patients combining multiple forms of genomic analysis. Identity of bacterial species and anatomic distribution of preoperative strains were correlated with identity and antimicrobial resistance of the pathogens of the 14 (6.8%) occurring surgical site infections. There was a significant anatomic correlation between the preoperative microbiome on the back skin and the microbiology of postoperative surgical site infections (Staphylococci correlated with cephalad skin, Escherichia and Enterobacter with lumbosacral skin). Strains causing postoperative wound infections were present in the preoperative microbiome and their preoperative antibiotic resistance profile correlated with prophylaxis-resistant postoperative infections. A total of 86% of surgical site infections originated endogenously from preoperative strains, and 59% were resistant to the prophylactic antibiotic administered during surgery. Molecular analysis of all spine surgical site infections occurring within the shared perioperative environment during the study period showed no evidence of exogenous infections from shared nosocomial reservoirs.

Take home message: While sterility of the physical environment remains the cornerstone of modern wound infection prevention, this study emphasizes the need for surgical site infection prevention strategy tailored to the patient-specific preoperative microbiome and its resistance to antibiotics.