Abstract
<title>Abstract</title> <p>Background Optimizing preoperative skin antisepsis is critical for preventing surgical site infections (SSIs), yet the optimal formulation for high-risk abdominal procedures remains debated, particularly regarding its interaction with patient adiposity. This study aimed to evaluate the synergistic efficacy of alcohol-based versus aqueous povidone-iodine (PVP-I) in eradicating residual skin flora and preventing SSIs in elective laparotomies, isolating the moderating effect of Body Mass Index (BMI). Methods This prospective, laboratory-blinded, parallel-group, randomized controlled trial was conducted at two tertiary-care academic centers. Eighty adult patients (aged 18–55 years) undergoing elective laparotomy were randomized (1:1). To control for confounding immunologic and healing factors, patients with diabetes mellitus, immunodeficiency, or a history of previous laparotomies were systematically excluded. Following a standardized primary mechanical scrub with 7.5% PVP-I, participants received a final surgical paint with either 10% aqueous PVP-I (control, n = 40) or 10% PVP-I combined with 70% isopropyl alcohol (intervention, n = 40). The primary outcome was residual microbial load eradication. The secondary outcome was 30-day SSI incidence, monitored via 24-hour bedside evaluation and active 10-day interval telemedicine follow-ups. Results Baseline microbial loads were identical. Following final preparation, residual contamination persisted in 25.0% of the aqueous group versus only 12.5% of the alcohol-based group (Absolute Risk Reduction = 12.5%; Number Needed to Treat = 8). All reported SSIs (7.5% in control vs. 2.5% in intervention; P = 0.164) were superficial incisional. Multivariable logistic regression confirmed higher BMI as an independent risk factor for residual contamination (OR, 1.129; P = 0.016) and demonstrated that aqueous PVP-I was associated with a 2.8-fold increased odds of contamination relative to the synergistic formulation (OR, 2.807; P = 0.012). Conclusions Incorporating 70% isopropyl alcohol into 10% PVP-I significantly enhances resident flora eradication prior to laparotomy, effectively neutralizing anatomical barriers such as adiposity. While this provides a definitive microbiological advantage, larger multi-center trials are required to definitively prove clinical superiority in SSI reduction. Trial Registration: Iranian Registry of Clinical Trials: IRCT20250329065171N1. Registered 09 April 2025.</p>