Table 2.

Risk factors for SSI.

Variable	Coding	n	SSI	SSI rate (%)	OR	95% CI OR	P value
Age (years)	≤ 72	6547	144	2.20	Ref
	> 72	6346	169	2.66	1.22	0.97–1.52	0.09
Preoperative stay (days)	≤ 2	6810	167	2.45	Ref
	> 2	817	23	2.82	1.15	0.74–1.79	0.53
Wound classification	2	12,312	298	2.42	Ref
	3	440	14	3.18	1.32	0.77–2.28	0.31
ASA score	1 and 2	8357	178	2.13	Ref
	3 and 4	4132	122	2.96	1.40	1.11–1.77	0.005
Operative time (min)	≤ P75	9075	223	2.46	Ref
	> P75	3818	90	2.36	0.96	0.75–1.23	0.74
NNIS	0	5528	121	2.19	Ref
	1	5268	127	2.47	1.10	0.86–1.42	0.31
	2 and 3	1474	50	3.39	1.57	1.12–2.19	0.01
Length of stay (days)	≤ 5	9941	193	1.94	Ref
	> 5	2952	120	4.07	2.14	1.70–2.70	< 10–4
Follow-up (days)	≤ 36	2289	124	4.69	Ref
	> 36	5339	66	0.03	0.01	0.00–0.03	< 10–4