Morar 2015.

Study characteristics
Methods	Retrospective cohort. Study period: 2005 to 2010
Participants	Country: United Kingdom. CD patients who underwent ileocolonic resection. Patients with previous segmental or subtotal colectomy were excluded
Interventions	1. Preoperative steroids (n= 34) 2. Preoperative immunomodulators (n= 64) 3. Preoperative 5ASA (n= 43) 4. Preoperative anti‐TNF therapy (n= 4) within 4 weeks of surgery 5. No preoperative steroids (n= 104) 6. No preoperative immunomodulators (n= 193) 7. No preoperative 5ASA (n= 82) 8. No preoper a tive anti‐TNF therapy (n= 126)
Outcomes	Intrabdominal septic complication including anastomotic leak, intraabdominal collection, enter o cutaneous fistula formation within 30 days of surgery
Notes	NOS very high risk of bias ov erall Adjusted OR for preoperative anti‐TNF therapy was obtained from multivariate regression model.
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	CD patients who underwent ileocolonic resection from 2005 to 2010
Selection of the non exposed cohort	Low risk	Both groups obtained from the same databases and time period
Ascertainment of exposure	Low risk	Clinical case records were examined
Demonstration that outcome of interest was not present at start of study	High risk	Fistula/abscess was indication for surgery for some patients
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	Low risk	Clinical case records were examined
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Low risk	Low percentage of patients had missing data (<15%)