Study design

We conducted an institutional retrospective study on patients that underwent elective open surgical interventions over the course of a 3-year period, from June 2018 to June 2021. The patients involved in the study were treated under the surgical units of breast and endocrine surgery, hepato-pancreatico-biliary surgery, colorectal surgery and vascular surgery.

Study setting

This study was conducted at Tikur Anbessa Specialized Hospital, the largest academic medical center in Ethiopia. It is located in the capital city, Addis Ababa and provides both medical and educational services at a sub-specialty level.

Sample size

A 50% population proportion was used because of absence of previous studies which brought the sample size to 384. Only 244 patients during the time period fulfilled the inclusion criteria. Using the finite population calculation the sample size became 150. But to increase the power of the study and improve on its generalizability, all the patients that fulfilled the inclusion criteria were included.

Study participants

All patients with age of ≥ 14 years whom underwent major surgical intervention using open technique with clean and clean contaminated wounds over the 3 years period of the study.

Inclusion criteria

All elective surgery patients that underwent open surgery for endocrine surgery, breast surgery, hepato-pancreato-biliary surgery, colorectal surgery, and upper GI surgery are included. All included patients had clean and clean contaminated wound class. Every patient that were include are of the age of ≥ 14 years.

Exclusion criteria

All pediatric patients that were surgically managed at the hospital.

Patients admitted for nonsurgical or minimally invasive modes of treatment and those that were either discharged or died before any surgical intervention was performed.

Study variablesIndependent variables

Age, gender, comorbidities, wound classification, type of surgery, prophylactic antibiotics administration, timing of antibiotics administration, intraoperative blood loss, duration of surgery, and re-administration of antibiotics.

Dependent variables

The primary outcome was the rate of “extended” postoperative antibiotics administration, and the secondary outcome was the rate of surgical site infections.

Data sources

The data were collected from the patients’ medical records retrieved physically from a paper chart using a data collection tool created and validated before the start of the study. This tool included socio-demographic, clinical, and outcome data.

Measurement/analysis and interpretation

After the data have been collected, it was coded, cleaned, and entered into IBM SPSS Statistics for Windows, Version 24.0. Armonk, NY: IBM Corp. The outliers were sought for and corrected. Afterward, the data was analyzed using the same software using a descriptive and inferential statistical models.

Study size

All patients fulfilling the inclusion criteria over the predetermined study period of 3 years well included in the study.

Statistical methods

Initially, descriptive analysis was used to determine the mean and standard deviations of the parametric variables used in the study. Categorical variables were analyzed using frequency distribution tables. Dependent variables were cross-tabulated with the independent study variables, and univariable analysis was performed. Those factors that were determined by the univariable analysis to potentially impart the dependent variables’ outcomes were analyzed with multivariable logistic regression and the values were presented as adjusted odds ratios with a p-value.

Ethical considerations

Ethical approval was acquired from the Institutional Review Board of Addis Ababa University, College of Health Sciences, which is the governing body of health sciences researches under the jurisdiction of Addis Ababa University. The study was conducted in accordance to Helsinki declarations, Ethiopian National Research Ethics Guidelines, and Institutional regulations on research ethics. All the data collected were handled confidentially and no entity outside of the investigators had any access to any of the patient information.