Daniels 2017.

Study characteristics
Methods	RCT, multicentre; 22 clinical sites in the Netherlands, from 1 June 2010 to 14 October 2012 Van Dijk 2018: two‐years follow‐up study
Participants	570 patients randomised; 42 patients excluded with adequate reasons (no‐AB: 262 vs. AB: 266) Inclusion: Left‐sided, CT‐verified diverticulitis Exclusion: Previously US‐ or CT‐verified diverticulitis, inflammatory bowel disease, complicated diverticulitis, conditions with expected survival < 6 months, pregnancy, breastfeeding, ASA > III, clinical suspicion of sepsis, immunocompromised, AB in four weeks before inclusion. Van Dijk 2018: Sixty participants were lost to follow‐up (No‐AB: 35 vs. AB: 25). Participants included: 468 (No‐AB: 227 vs. AB: 241)
Interventions	Intervention: No‐AB. Could be treated directly in an outpatient setting Control: AB‐group: Amoxicillin‐clavulanic acid, 10‐day course, IV 1200 mg x 4 for at least 48 hours → oral 625 mg x 3 ciprofloxacin and metronidazole The AB treatment led to admission of all participants on the premise that treatment was started IV.
Outcomes	Primary: Time to recovery during 6 months of follow‐up (median days) Criteria: discharge from hospital, normal diet, temperature less than 38°C, VAS pain score below 4 (with no use of daily pain medication), and resumption of pre‐illness working activities as assessed by a daily patient diary Secondary: At 2 and 6 months, the participant visited the outpatient clinic; follow‐up at 12 and 24 months was by telephone. A standard case record form was used for collection of study variables. Oracle® Clinical, with internet‐based remote data capture, version 4.5.3 (Oracle, Redwood Shores, California, USA), was used for entering, managing and validating data. 1. Proportion of time outside hospital in the 6‐month period  2. Readmission rate within 6 months  3. Complicated diverticulitis within 6 months (abscess, perforation, obstruction/stricture, diverticular bleeding or fistula)  4. Ongoing diverticulitis within 6 months  5. Recurrent diverticulitis within 6 months  6. Need for sigmoid resection within 6 months: Emergency  Elective  7. Need for sigmoid resection within 12 months of follow‐up  8. Adverse events  9. All‐cause mortality  Van Dijk 2018:  Follow‐up was performed by telephone at 12 and 24 months and all hospital records were reviewed. Recurrent diverticulitis was assessed clinically with or without imaging.
Notes	The DIABOLO trial was funded by the Netherlands Organization for Health Research and Development (ZonMw; 171002303) and the Digestive Diseases Foundation (Maag Lever Darm Sticht‐ ing, MLDS WO08‐54). The funders had no involvement in trial design, conduct or reporting. The authors declared no conflict of interest. Van Dijk 2018: The authors declared no conflict of interest.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation controlled centrally by computer system; block randomisation in sizes 2 or 4
Allocation concealment (selection bias)	Low risk	Outcome was generated automatically, thereby preserving concealment.
Blinding (performance bias and detection bias) All outcomes	High risk	No blinding
Incomplete outcome data (attrition bias) All outcomes	High risk	In total, 570 participants randomised. 70 were excluded with adequate reasons (No‐AB: 34 vs. AB: 36). 16 participants were lost to follow‐up (No‐AB: 6 vs. AB: 10). In total, 86 participants did not complete the trial corresponding to an attrition rate of 15% which was acceptable and reasons for exclusion were justified. Group sizes with α = 0·05 and a power of 99 per cent were calculated and reported to be 262 in each group; which gave sufficient power. Van Dijk 2018: The authors believed that attrition bias could have been introduced in the multiple analyses that were done. They showed an association with earlier dropout of follow‐up in the no‐AB group compared to the AB group, when recovery of the initial diverticulitis episode was prolonged. The authors suggested that the reason for the correlation was the open‐label design. However, baseline characteristics in the 6‐month and the 2‐years follow‐up were comparable. 570 patients randomised. 42 were excluded with adequate reasons and 60 were lost to follow‐up. In total, 102 participants did not complete the trial corresponding to an attrition rate of 17.9% which was acceptable and reasons for exclusion were justified.
Selective reporting (reporting bias)	Low risk	Method and primary and secondary outcomes were specified, published and available during the study (Unlu 2010).