Cohen 2019.

Study characteristics
Methods	Multicentre prospective cohort study. Study period 2014 to 2017.
Participants	Country: USA. Crohn's and ulcerative colitis patients undergoing intra‐abdominal surgery.
Interventions	1. Preoperative anti‐TNF therapy (n= 382) within 12 weeks of surgery. 2. No preoperative anti‐TNF exposure (n= 573)
Outcomes	30 post operative infectious complications (any infection and surgical site infection)
Notes	NOS low risk of bias overall Adjusted OR for preoperative anti‐TNF therapy was obtained from m ultivariable logistic regression model.
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	Prospective cohort of IBD patients who underwent intra‐abdominal surgery from 2014 to 2017
Selection of the non exposed cohort	Low risk	Both groups obtained from same centres and time period
Ascertainment of exposure	Low risk	Prospective database. Data obtained by patient interview and chart abstraction
Demonstration that outcome of interest was not present at start of study	Low risk	Controlled for pre‐operative non‐abdominal infection
Comparability of cohorts (Controlled for critical factor/other medications)	Low risk	Performed multivariable analysis controlling for preoperative methotrexate and steroids
Comparability of cohorts (Controlled for additional factor)	Low risk	Controlled for multiple other factors including age, BMI, gender and comorbid disease
Assessment of outcome	Low risk	Prospective database. Data obtained by patient interview and chart abstraction
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Unclear risk	Authors did not comment whether any patients were lost to follow up