El‐Hussuna 2012.

Study characteristics
Methods	Retrospective, multicenter (4 institutions) cohort. Study period: 2000 to 2007.
Participants	Country: Denmark. CD patients who underwent resection and anastomosis or with stricturoplasty
Interventions	1. Preoperative infliximab/certolizumab (n= 32) within 3 months of surgery 2. Azathioprine/6‐mercaptopurine/methotrexate (n= 166) within 1 month o surgery 3. Preoperative steroids (n= 66) 4. No preoperative anti‐TNF medication (n= 385) 5. No preoperative immunosuppressants (n= 251) 6. No preoperative steroids (n= 351)
Outcomes	Intraabdominal septic complications (anastomotic dehiscence, fistula, abscess), septic complications, other infective complications within 30 days of surgery
Notes	NOS very high risk of bias overall
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	CD patients who underwent resection form 2000 to 2007
Selection of the non exposed cohort	Low risk	Both groups obtained from the same hospitals and time period
Ascertainment of exposure	Unclear risk	No information provided
Demonstration that outcome of interest was not present at start of study	High risk	20% patients had preoperative intraabdominal infection
Comparability of cohorts (Controlled for critical factor/other medications)	High risk	Univariate analysis
Comparability of cohorts (Controlled for additional factor)	High risk	Univariate analysis
Assessment of outcome	Unclear risk	No information provided
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Unclear risk	No information provided