Table 2. Multiple logistic regression analysis of SSI risk factors by surgical procedure: SI-SSI and OS-SSI.

Gastrectomy
Variables	Open surgery				Laparoscopic surgery
	SI-SSI		OS-SSI		SI-SSI		OS-SSI
	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015
Sex (female as a reference)			1.60 (1.21–2.12)	1.76 (1.16–2.67)			1.80 (1.36–2.37)	1.93 (1.27–2.91)
Age: ≥ 65 years			1.66 (1.29–2.13)	1.52 (1.02–2.25)			1.69 (1.32–2.17)	1.53 (1.03–2.26)
Operation duration: ≥ T-time		1.52 (1.12–2.07)	4.24 (3.27–5.49)	2.76 (1.97–3.88)		1.49 (1.00–2.21)	3.51 (2.44–5.04)	2.03 (1.36–3.04)
Wound class: ≥ 3	3.44 (2.12–5.57)		2.32 (1.43–3.79)		3.44 (2.12–5.59)		2.36 (1.45–3.82)
ASA classification: ≥ 3		1.97 (1.40–2.78)				1.96 (1.39–2.77)
Emergency operation: Yes		2.77 (1.55–4.98)		2.64 (1.26–5.52)		2.73 (1.52–4.88)		2.40 (1.16–4.96)
Combined surgery: Yes			1.53 (1.19–1.99)	2.67 (1.60–4.47)			1.90 (1.48–2.44)	2.71 (1.61–4.55)
Silk suture: Yes		1.97 (1.20–3.24)		1.98 (1.15–3.41)		1.91 (1.16–3.14)
Cholecystectomy
Variables	Open surgery				Laparoscopic surgery
	SI-SSI		OS-SSI		SI-SSI		OS-SSI
	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015
Sex (female as a reference)			3.90(1.31–11.56)	5.53 (1.24–24.66)			3.58(1.20–10.64)
Age: ≥ 65 years	2.43 (1.51–3.91)				2.40 (1.49–3.86)
Operation duration: ≥ T-time		3.91 (2.21–6.90)	9.05 (3.59–22.86)	5.73 (1.96–16.76)	1.66 (1.02–2.70)	2.93 (1.87–4.59)	5.46 (2.24–13.31)	15.02 (3.31–68.20)
Wound class: ≥ 3	2.29 (1.36–3.85)	1.80 (1.04–3.11)	4.39 (1.89–10.18)		2.16 (1.28–3.64)		4.22 (1.83–9.72)
ASA classification: ≥ 3	2.21 (1.19–4.12)				2.18 (1.17–4.05)
Emergency operation: Yes	0.42 (0.21–0.84)
Stoma: Yes						9.84 (1.09–88.80)
Silk suture: Yes	3.00 (1.84–4.89)	27.70 (15.79–48.59)	2.40 (1.01–5.70)		2.74 (1.67–4.49)	25.68 (14.61–45.14)
Colectomy
Variables	Open surgery				Laparoscopic surgery
	SI-SSI		OS-SSI		SI-SSI		OS-SSI
	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015
Sex (female as a reference)				1.52 (1.03–2.22)				1.53 (1.05–2.24)
Age: ≥ 65 years			0.72 (0.52–1.00)
Operation duration: ≥ T-time			2.28 (1.62–2.21)	2.81 (1.94–4.07)			2.94 (1.93–4.50)	2.89 (1.96–4.26)
Wound class: ≥ 3	2.51 (1.90–3.33)	1.97 (1.52–2.55)	2.09 (1.37–3.20)		2.54 (1.92–3.37)	1.98 (1.53–2.57)	2.19 (1.43–3.35)
ASA classification: ≥ 3			1.53 (1.02–2.30)	1.63 (1.07–2.49)			1.52 (1.01–2.29)	1.62 (1.07–2.47)
Emergency operation: Yes		1.45 (1.12–1.88)	2.27 (1.54–3.35)			1.44 (1.12–1.87)	2.30 (1.56–3.39)
Combined surgery: Yes		0.22 (0.08–0.63)	1.69 (1.10–2.61)			0.22 (0.08–0.62)	1.65 (1.06–2.57)
Stoma: Yes	1.77 (1.35–2.31)	1.33 (1.04–1.69)		2.66 (1.74–4.05)	1.77 (1.35–2.32)	1.31 (1.03–1.66)		2.45 (1.61–3.72)
Silk suture: Yes		3.32 (2.54–4.33)		2.45 (1.44–4.16)		3.30 (2.53–4.31)		2.42 (1.43–4.09)
Rectal resection
Variables	Open surgery				Laparoscopic surgery
	SI-SSI		OS-SSI		SI-SSI		OS-SSI
	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015
Sex (female as a reference)			2.58 (1.81–3.69)				2.61 (1.83–3.73)
Operation duration: ≥ T-time		1.52 (1.09–2.14)	1.70 (1.19–2.43)			1.50 (1.03–2.17)
Wound class: ≥ 3	1.92 (1.28–2.86)		2.74 (1.80–4.18)	2.23 (1.08–4.61)	1.92 (1.28–2.87)		2.70 (1.77–4.11)	2.23 (1.08–4.61)
Emergency operation: Yes		2.50 (1.34–4.67)				2.42 (1.30–4.50)
Stoma: Yes	2.65 (1.99–3.52)	1.60 (1.15–2.23)			2.64 (1.99–3.50)	1.59 (1.13–2.22)
Silk suture: Yes		2.19 (1.41–3.38)				2.14 (1.39–3.30)
Appendectomy
Variables	Open surgery				Laparoscopic surgery
	SI-SSI		OS-SSI		SI-SSI		OS-SSI
	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015	2003–2009	2010–2015
Operation duration: ≥ T-time		1.82 (1.13–2.92)		5.30 (1.93–14.58)		1.79 (1.11–2.88)	2.18 (1.07–4.45)	4.69 (1.78–12.41)
Wound class: ≥ 3	2.65 (1.64–4.28)		14.26 (3.36–60.55)		2.64 (1.63–4.27)		14.10 (3.32–59.92)
ASA classification: ≥ 3	1.88 (1.00–3.51)	2.46 (1.24–4.87)			1.89 (1.01–3.54)	2.43 (1.22–4.82)
Stoma: Yes				96.03(10.81-852-75)				89.97(10.31–785.29)
Silk suture: Yes	1.57 (1.04–2.37)	10.31 (5.57–19.10)		5.87 (1.70–20.22)	1.58 (1.05–2.39)	10.44(5.64–19.36)		6.05 (1.76–20.80)