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Appendix 3 Subgroup analysis of different types of SSI

From: Optimal timing of surgical antimicrobial prophylaxis in laparoscopic surgery: a before-after study

  No SSI
(n = 1207)
Superficial SSI
(n = 113)
Deep and organ space SSI
(n = 77)
P value
No SSI vs superficial SSI No SSI vs deep and organ space SSI
Age, median, (IQR) years 66 (52–75) 67 (53–76) 72 (64–78) 0.49 < 0.001
 < 65, n (%) 554 (45.9) 50 (44.3) 21 (27.3) 0.74 0.018
 ≥ 65, n (%) 653 (54.1) 63 (55.7) 56 (72.7)   
Male gender, n (%) 532 (44.1) 57 (50.4) 17 (22.1) 0.19 < 0.001
Co-morbidities, n (%)
 Diabetes mellitus 164 (13.6) 13 (11.5) 15 (19.5) 0.53 0.15
 Chronic lung diseases 57 (4.7) 6 (5.3) 6 (7.8) 0.78 0.23
 Cardiovascular diseases 59 (4.9) 7 (6.2) 3 (3.9) 0.54 0.69
 Hypertension 442 (36.6) 38 (33.6) 33 (42.9) 0.53 0.27
 Dyslipidemia 198 (16.4) 19 (16.8) 14 (18.2) 0.91 0.68
Current smoker, n (%) 560 (46.4) 58 (51.3) 52 (67.5) 0.32 < 0.001
ASA score, n (%)
 1 (no disturbance) 250 (20.7) 22 (19.5) 7 (9.1) Ref. Ref.
 2 (mild disturbance) 854 (70.8) 82 (72.6) 62 (80.5) 0.73 0.02
 3 (severe disturbance) 99 (8.2) 9 (8.0) 8 (10.4) 0.94 0.05
 4 (life-threatening) 4 (0.3) 0 (0) 0 (0) N/A N/A
Wound class, n (%)
 2 clean-contaminated 1202 (99.6) 112 (99.1) 76 (98.7) 0.48 0.27
 3 contaminated 5 (0.4) 1 (0.9) 1 (1.3) 0.48 0.27
Emergent surgery, n (%) 200 (16.6) 16 (14.2) 6 (7.8) 0.51 0.04
Type of surgery, n (%)
 Cholecystectomy 291 (24.1) 11 (9.7) 5 (6.5) Ref. Ref.
 Gastrectomy 294 (24.4) 28 (24.8) 49 (63.6) 0.011 < 0.001
 Appendectomy 140 (11.6) 14 (12.4) 3 (3.9) 0.019 0.77
 Colectomy 175 (14.5) 16 (14.2) 9 (11.7) 0.028 0.05
 Proctectomy 306 (25.4) 44 (38.9) 11 (14.3) < 0.001 0.18
 Cholecystectomy and appendectomy 1 (0.1) 0 (0) 0 (0) N/A N/A
Operation time, median, (IQR) min 205 (131–285) 229 (164–296) 325 (271–399) 0.015 < 0.001
  < 180, n (%) 502 (41.6) 33 (29.2) 9 (11.7) 0.01 < 0.001
  ≥ 180, n (%) 705 (58.4) 80 (70.8) 68 (88.3)   
SAP drip infusion time, median, (IQR) min 18 (14–23) 18 (14–25) 17 (13–22) 0.52 0.46
Time from SAP completion to surgical incision, median, (IQR) min 12 (4–25) 14 (2–31) 17 (6–29) 0.39 0.69
Time windows, n (%)
 31–60 min 175 (14.5) 24 (21.2) 18 (23.4) Ref. Ref.
 < 0 min 143 (11.9) 18 (15.9) 5 (6.5) 0.80 0.04
 0–30 min 861 (71.4) 65 (57.5) 54 (70.1) 0.02 0.08
 > 60 min 26 (2.2) 6 (5.3) 0 (0) 0.30 N/A
Intervention status, “yes” 395 (32.7) 35 (31.0) 25 (32.5) 0.70 0.83
  1. NOTE. SSI surgical site infection, IQR interquartile range, ASA American Society of Anesthesiologists, SAP surgical antimicrobial prophylaxis, N/A not applicable