Poisson regression for the effect of season on dSSI rates over time (laminectomy and spinal fusion/revision fusion).
| Period | Patients (n = 22,568) | No. of dSSI (n = 225) | dSSI Rate (%) | Rate Ratio (95% CI)a | P Value |
| Overall | 22,568 | 225 | 0.99 | 0.91 (0.87, 0.95) | <0.01 |
| Season | |||||
| Summer (reference variable) | 5868 | 66 | 1.12 | --- | -- |
| Fall | 5081 | 40 | 0.79 | 0.67 (0.45, 0.99) | 0.05 |
| Winter | 5552 | 55 | 0.99 | 0.87 (0.61, 1.25) | >0.05 |
| Spring | 6067 | 64 | 1.05 | 0.94 (0.61, 1.25) | >0.05 |
Abbreviation: dSSI, deep surgical site infection.
Note: Boldface indicates statistically significant findings.
↵a Rate ratio obtained from Poisson regression.