Uchino 2019.

Study characteristics
Methods	Retrospective cohort study. Study period 2015 to 2018
Participants	Country: Japan. Patients with ulcerative colitis who underwent total colectomy with ileostomy, total proctocolectomy with end ileostomy or ileal pouch anal anastomosis
Interventions	1. Preoperative steroids (n=117) 2. Preoperative azathioprine/6MP (n=121) 3. Preoperative anti‐TNF agents within 12 weeks of surgery (n=146)
Outcomes	Surgical site infection (incisional infection and organ/space infection) within 30 days of surgery
Notes	NOS very high risk of bias overall Adjusted OR for preoperative anti‐TNF therapy was obtained from multivariable regression model. Unadjusted OR for preoperative steroid therapy was obtained from univariate regression model.
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	301 consecutive patients with UC who underwent abdominal surgery
Selection of the non exposed cohort	Low risk	Both groups obtained from the same hospital and time period
Ascertainment of exposure	Low risk	Retrospective evaluation of a prospective database at Hyogo College of Medicine
Demonstration that outcome of interest was not present at start of study	Unclear risk	Information not provided
Comparability of cohorts (Controlled for critical factor/other medications)	High risk	Did not perform
Comparability of cohorts (Controlled for additional factor)	High risk	Multivariate analysis only for anti‐TNF administration (age, pre‐op albumin, transfusion, ASA score, wound class, urgent/emergent surgery, intra‐operative blood loss and duration of surgery). Univariate analysis for steroids and azathioprine/6M
Assessment of outcome	Low risk	Retrospective evaluation of a prospective database at Hyogo College of Medicine
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Unclear risk	Information not provided