Abis 2019.

Methods	Study design: randomised clinical trial Duration of trial: May 2013 to March 2017 Duration of follow‐up: follow‐up was done at least twice a year in the first 2 years after surgery and then yearly according the Dutch guidelines on colorectal cancer Country of origin: the Netherlands
Participants	Baseline characteristics Number randomised: 485 Number analysed: 565 Number of eligible participants that could be included in our meta‐analysis: 316 Only study patients who underwent preoperative mechanical bowel preparation (left‐sided colonic, sigmoid and low anterior resections) can be included in our meta‐analysis. A request to the study authors to provide us with the primary data for the inclusion of eligible patients from the study has not yet been fulfilled.
Interventions	Comparison Intervention: SDD Control: no oral antibiotics Mechanical bowel preparation Was given for left‐sided colectomies, sigmoid and anterior resections. Oral antibiotics Oral colistin, tobramycin and amphotericin B were administered to patients in the SDD group to decontaminate the digestive tract. Perioperative intravenous antibiotic prophylaxis Both treatment and control group received intravenous cefazolin and metronidazole for perioperative prophylaxis.
Outcomes	Outcomes sought in review and reported in trial SSI Anastomotic leakage Mortality Incidence of postoperative ileus Length of hospital stay Outcomes sought but not reported in trial Postoperative complications (mild D/C I + II or severe D/C III+IV) Side effects of Intervention(s) Outcomes reported in trial but not used in review Reoperation Urinary tract infection Pulmonary complications Pulmonary embolism Cardiac Fascial dehiscence
Notes	Source of funding: this study was funded by the DutchDigestive Foundation, Spaarne Gasthuis Academy Fund. The funder had no role in study design, data collection, data analysis, data interpretation or writing of the report. Conflicts of interest: the authors declare no conflict of interest Ethics approval: the ethics board at the VU University Medical Centre and the institutional review board at each participating centre approved the study. Informed consent: all patients provided written informed consent. Clinical trials registration: the trial was registered with ClinicalTrials.gov (number NCT01740947). Sample size calculation: considering a 9 per cent anastomotic leakage rate in the control group, based on numbers of the Dutch Surgical Colorectal Audit at onset of the trial, and an estimated 4 percent in the intervention group, 381 patients needed to be included per treatment arm (total of 762 patients).

SDD:  selective decontamination of the digestive tract; SSI: surgical site infections