Individualized antibiotic prophylaxis reduces surgical site infections by gram-negative bacteria in instrumented spinal surgery.

PURPOSE: Surgical site infection (SSI) can be a challenging complication after posterior spinal fusion and instrumentation (PSFI). An increasing rate of SSI by gram-negative bacteria (GNB) has been observed. Current guideline recommendations have not been effective for preventing infection by these microorganisms. METHODS: Retrospective cohort study comparing two consecutive groups of patients undergoing PSFI at a single institution. Cohort A includes 236 patients, operated between January 2006 and March 2007, receiving standard preoperative antibiotic prophylaxis with cefazolin (clindamycin in allergic patients). Cohort B includes 223 patients operated between January and December 2009, receiving individualized antibiotic prophylaxis and treatment based on preoperative urine culture. Cultures were done 3-5 days before surgery in patients meeting one of the following risk criteria for urinary tract colonization: hospitalization longer than 7 days, indwelling catheter, neurogenic bladder, history of urinary incontinence, or history of recurrent urinary tract infection. RESULTS: Twenty-two (9.3%) patients in cohort A developed SSI, 68.2% due to GNB. 38 (17%) patients in cohort B were considered at risk for GNB colonization; preoperative urine culture was positive in 14 (36%). After adjusted antibiotic prophylaxis, 15 (6.27%) patients in cohort B developed SSI, 33.4% due to GNB. A statistically significant reduction in GNB SSI was seen in cohort B (Fisher's exact test, p = 0.039). CONCLUSION: Higher preoperative GNB colonization rates were found in patients with neurogenic bladder or indwelling catheters. Preoperative bacteriological screening, treatment for bacteriuria, and individualized antibiotic prophylaxis were effective for reducing GNB SSI.