Biffi 2012.

Methods	2‐arm RCT conducted in Italy
Participants	121 participants undergoing elective surgery for colorectal cancer Inclusion criteria: undergoing elective surgery for colorectal cancer by laparotomic approach Exclusion criteria: history of allergy to dressing components; evidence of active infection at, or adjacent to, the operative site; coagulopathy (defined as platelet count < 50,000 cells/μL or a prothrombin time > 18 seconds); intestinal obstruction; active bowel bleeding; life expectancy < 6 months; inability to give written informed consent; or a programme of minimally invasive surgery planned (laparoscopy or robot‐assisted)
Interventions	Group A (n = 62): silver hydrofibre dressing (Aquacel Ag, ConvaTec) Group B (n = 59): standard absorbant dressing (Mepore, Molnlycke Health Care, Gothenburg, Sweden) All participants received a preoperative scrub and then painting with an aqueous solution of 10% povidone iodine, mechanical bowel preparation, and antibiotic prophylaxis in agreement with predefined protocols.
Outcomes	Primary review outcomes: SSI (clinical assessment) Secondary review outcomes: none
Notes	Follow‐up: 30 days We contacted the author about methods
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "To help match the two groups and address potential inter‐hospital differences, randomization was stratified by hospital with the use of computer‐generated randomization numbers without blocking." Comment: adequate
Allocation concealment (selection bias)	Low risk	Quote: "In order to maintain the double‐blind characteristic of this trial, some actions were taken. First, the generator of the assignment was a data manager, who was separated from the executor." Comment: not clear if the executor of randomisation had access to the full randomisation schedule or was separate from it at point of randomisation. However, the staff were blinded to treatment and the separation was confirmed by the trial author.
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "The Aquacel Ag Hydrofiber dressing was covered by a common wound dressing in the experimental arm, whereas a double common dressing was applied to patients of the control group to blind the patient, the nursing and the medical staff and the independent data collector as to the nature of the dressing used. Whenever SSI was suspected or diagnosed, clinically relevant microbiologic samples were cultured. Investigators, who were unaware of the patients’ group assignments, assessed the seriousness of all adverse events and determined whether they were related to the trial." Comment: blinded outcome assessment conducted.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Flow chart shows that 58/62 participants randomised to the intervention arm (4 lost to follow‐up) and 54/59 randomised to control arm were analysed (5 lost). Less than 10% lost in each arm, the impact of this loss unclear.
Selective reporting (reporting bias)	Low risk	None noted. Protocol not obtained.
Other bias	Low risk	None noted based on available information.