Effect of Intrawound Vancomycin Powder on the Pathogen Spectrum and Antimicrobial Susceptibility of Postoperative Infections in Elective Lumbar Fusion

STUDY DESIGN: Secondary microbiological analysis of a patient-blinded, single-center randomized controlled trial. OBJECTIVE: To determine whether intrawound vancomycin powder alters the surgical site infection (SSI) pathogen spectrum and gram-status distribution, selects for vancomycin- or methicillin-resistant organisms, or affects the rate of non-wound infections after elective posterior lumbar interbody fusion. SUMMARY OF BACKGROUND DATA: Intrawound vancomycin powder is widely used to prevent SSI after lumbar fusion, but retrospective data raise concerns about a gram-negative pathogen shift and resistance selection; randomized evidence is limited. METHODS: Adults undergoing elective posterior lumbar interbody fusion were enrolled between August 2015 and April 2019. Of 308 randomized, 292 were analyzed (Control, n=152; Vancomycin, n=140). All received intravenous cefuroxime; Vancomycin patients additionally received 1 g vancomycin powder before closure. We assessed the SSI pathogen spectrum and gram-status distribution, vancomycin and methicillin susceptibility, and non-wound infection rates. Wound cultures were tested to EUCAST breakpoints; Fisher's exact test with Wilson 95% CIs was used. RESULTS: Gram-positive organisms dominated both groups (7 of 8 [88%] vs. 3 of 3 [100%]) with no gram-negative shift; isolates included Cutibacterium acnes (n=4), MSSA, MRSE (n=2 each), S. saccharolyticus, E. cloacae, plus one polymicrobial case. Vancomycin susceptibility was preserved in 9 of 9 (100%); no VRE, VRSA, or MRSA occurred; both MRSE isolates were Control. Non-SSI events were equivalent (8 of 152 [5.3%] vs. 6 of 140 [4.3%]; P=0.788), dominated by urinary-tract pathogens. CONCLUSIONS: Intrawound vancomycin powder did not alter the gram-positive-dominated SSI spectrum, did not select for vancomycin- or methicillin-resistant organisms, and had no systemic effect on non-wound infections. These randomized data support empiric regimens retaining gram-positive coverage when SSI is suspected after lumbar fusion. LEVEL OF EVIDENCE: Level of Evidence: 1b.