The Barts Surgical Infection Risk (B-SIR) tool: external validation and comparison with existing tools to predict surgical site infection after cardiac surgery

Objective: Further to previous development and internal validation of the Barts Surgical Infection Risk (B-SIR) tool, this study sought to explore the external validity of the B-SIR tool and compare it with the Australian Clinical Risk Index (ACRI), and the Brompton and Harefield Infection Score (BHIS). Study design and setting: This multi-centre retrospective analysis of prospectively collected local data included adult (age >= 18 years) patients undergoing cardiac surgery between January 2018 and December 2019. Pre-pandemic data were used as a reflection of standard practice. Area under the curve (AUC) was used to validate and compare the predictive power of the scores, and calibration was assessed using the Hosmer-Lemeshow test and calibration plots. Results: In total, 6022 patients from three centres were included in the complete case analysis. The mean age was 66 years, 75% were men and 3.19% developed a surgical site infection (SSI). The B-SIR tool had an area under the curve (AUC) of 0.686 [95% confidence interval (CI) 0.649-0.723], similar to the developmental study (AUC 0.682, 95% CI 0.652- 0.713). This was significantly higher than the BHIS AUC of 0.610 (95% CI 0.045-0.109; P <0.001) and the ACRI AUC of 0.614 (95% CI 0.041-0.103; P <0.001). After recalibration using a correction factor, the B-SIR tool gave accurate risk predictions (Hosmer- Lemeshow test P 0.423). The multiple imputation result (AUC 0.676, 95% CI 0.639- 0.712) was similar to development data, and higher than the ACRI and BHIS. Conclusion: External validation indicated that the B-SIR tool predicted SSI after cardiac surgery better than the ACRI and BHIS. This suggests that the B-SIR tool could be useful for use in routine practice.