Study design:

Retrospective cohort study.

Objective:

To evaluate differences in readmission rates, number of debridements, and length of antibiotic therapy when comparing bacterial gram type following lumbar spinal fusion infections.

Summary of background data:

Surgical site infections (SSIs) after spinal fusion serve as a significant source of patient morbidity. It remains to be elucidated how bacterial classification of the infecting organism affects the management of postoperative spinal SSI.

Methods:

Patients who underwent spinal fusion with a subsequent diagnosis of SSI between 2013-2019 were retrospectively identified. Patients were grouped based on bacterial infection type (gram-positive, gram-negative, or mixed infections). Poisson’s regressions analyzed the relationship between the type of bacterial infection and the number of incision and debridement (I&D) reoperations, and the duration of IV antibiotic therapy. Significance was set at P<0.05.

Results:

Of 190 patients, 92 had gram-positive (G+) infections, 57 had gram-negative (G-) infections, and 33 had mixed (M) infections. There was no difference in 30- or 90-day readmissions for infection between groups (both P=0.051). Patients in the M group had longer durations of IV antibiotic treatment (G+: 46.4 vs G-: 41.0 vs M: 55.9 d, P=0.002). Regression analysis demonstrated mixed infections were 46% more likely to require a greater number of debridements (P=0.001) and 18% more likely to require an increased duration of IV antibiotic therapy (P<0.001), while gram-negative infections were 10% less likely to require an increased duration of IV antibiotic therapy (P<0.001) when compared to G- infections.

Conclusion:

Spinal SSI due to a mixed bacterial gram type results in an increased number of debridements and a longer duration of IV antibiotics required to resolve the infection compared to gram-negative or gram-positive infections.

Level of evidence:

3.