Poisson regression for the effect of season on dSSI rates over time (spinal fusion/revision fusion).
| Period | Patients (n = 14,637) | No. of dSSI (n = 180) | dSSI Rate (%) | Rate Ratio (95% CI)a | P Value |
| Overall | 14,637 | 180 | 1.23 | 0.89 (0.84, 0.94) | <0.01 |
| Season | |||||
| Summer (reference variable) | 3780 | 50 | 1.32 | --- | --- |
| Fall | 3356 | 29 | 0.86 | 0.62 (0.39, 0.98) | <0.05 |
| Winter | 3600 | 47 | 1.31 | 0.98 (0.66, 1.46) | >0.05 |
| Spring | 3901 | 54 | 1.38 | 1.05 (0.71, 1.54) | >0.05 |
Abbreviation: dSSI, deep surgical site infection.
Note: Boldface indicates statistically significant findings.
↵a Rate ratio obtained from Poisson regression.