Poisson regression for the effect of season on dSSI rates over time (laminectomy).
| Time Period | Patients (n = 7931) | No. of dSSI (n = 38) | dSSI Rate (%) | Rate Ratio (95% CI)a | P Value |
| Overall | 7931 | 38 | 0.48 | 1.02 (0.90, 1.15) | >0.05 |
| Season | |||||
| Summer (reference variable) | 2088 | 15 | 0.72 | --- | -- |
| Fall | 1725 | 8 | 0.46 | 0.65 (0.28, 1.54) | >0.05 |
| Winter | 1952 | 8 | 0.41 | 0.57 (0.24, 1.35) | >0.05 |
| Spring | 2166 | 7 | 0.32 | 0.45 (0.18, 1.10) | >0.05 |
Abbreviation: dSSI, deep surgical site infection.
↵a Rate ratio obtained from Poisson regression.