There is controversy about the maximum number of elements to be included in a surgical site infection (SSI) prevention bundle and the possibility of its implementation at a multi-center level.

This study analyzes SSI rates in colorectal surgery after the implementation of two preventive bundles.

The investigators hypothesized that the thorough introduction of a well-designed large bundle of best practice preventive measures would result in good adherence and greater reduction of SSI rates after colorectal surgery.

To better understand the impact of adding new measures to an established bundle within a national surveillance program and to measure the effectiveness of each specific measures, the effect of a six-measure and a ten-measure bundle sequentially implemented on a large series of elective colorectal procedures from 2011 to 2022 was analized. In addition, it will be investigated whether taking advantage of a national surveillance programme for post-operative infections can facilitate the implementation of the packages.

Setting and patients. This is a pragmatic, cohort, multicentre study of a network of 65 public and private hospitals prospectively collecting data from elective colorectal surgery to minimise surgical site infection (SSI) rates and improve care. Prospective surveillance is conducted by each hospital's infection control team to ensure adequate data collection with a mandatory minimum follow-up of 30 days after surgery and electronic chart review checking readmissions, emergency department visits, microbiological and radiological data.

Patients undergoing elective colorectal surgery between January 2011 and December 2022 will be included. Cases with class 2 (clean-contaminated) and 3 (contaminated) wounds, according to the National Healthcare Safety Network classification, will be followed up. Patients with class 4 wounds (peritonitis) and previous ostomies are excluded.

Three sequential phases will be compared: a baseline period before package implementation (Baseline Group), from January 2011 to June 2016; a Bundle-1 period after implementation of a package of six measures (Bundle-1 Group), from July 2016 to June 2018; and a Bundle-2 period after implementation of a package of ten measures (Bundle-2 Group), from July 2018 to December 2022.

Definitions, study results and variables. The SSIs are defined according to the definitions of the Centers for Disease Control and Prevention.

The primary objective will be to analyse the effect of the implementation of the package on the prevention of SSIs and their subtypes and to assess compliance and effectiveness of individual measures. Secondary outcomes will be length of stay, mortality and micro-organisms causing SSIs.

Intervention. In the Reference Group, some measures such as intravenous antibiotic prophylaxis and the use of laparoscopy were included as standard clinical practice. In Bundle-1, six well-documented colorectal-specific measures were introduced: intravenous antibiotic prophylaxis, laparoscopy, oral antibiotic prophylaxis, mechanical bowel preparation, normothermia and double-ring plastic wound retractor. In Bundle-2, four additional general measures were incorporated in addition to the above: adequate depilation, skin antisepsis with 2% chlorhexidine gluconate in alcohol, perioperative glucose control and instrument change before wound closure.

Inclusion Criteria:

• Colon or rectal elective surgery.

Exclusion Criteria:

Peritonitis at the time of intervention ("dirty" surgery) Patients who underwent multiple procedures during the same surgery, for example resection of liver metastases Centers that performed less tan 10 surgical procedures annually Centers that have not been able to ensure prospective surveillance during hospitalization or effective monitoring of cases within 30 days of the intervention

Data will be shared if requested