Risk factors for mortality in patients with diabetic foot infections: a prospective cohort study

Background: An increasing prevalence of diabetes mellitus has led to a high risk of diabetic foot infections (DFI) and associated morbidity. However, little is known about the relationship between DFI and mortality.

Aim: To investigate the risk of mortality and associated factors in patients with DFI in an Australian context.

Methods: A prospective cohort study of inpatients with DFI between May 2012 and October 2016 was done at Royal Darwin Hospital, a tertiary referral hospital for the Top End of the Northern Territory. Primary outcome was 1-year mortality with Cox regression analysis undertaken to assess risk factors for mortality.

Results: Four hundred and thirteen consecutive adult diabetic patients with 737 admissions were referred to the High-Risk Foot Service for DFI. Cumulative risk of mortality at 1 year was 8.9% (95% confidence interval (CI) 6.4–12.2). On univariable analysis, mortality was associated with older age (hazard ratio (HR) per year increase 1.08, 95% CI 1.06–1.11, P = 0.001), haemodialysis (HR 3.64, 1.74–7.62, P < 0.001), isolation of Pseudomonas aeruginosa (HR 2.32, 1.05–5.12, P = 0.04) and ischaemic heart disease (HR 2.05, 1.04–4.07, P = 0.04), while indigenous status (HR 0.48, 0.25–0.95, P = 0.04) and HbA1c > 7% (HR 0.45, 0.20–0.99, P < 0.05) were protective. After adjusting for confounders, independent risk factors for mortality were haemodialysis (adjusted HR 5.76, 95% CI 2.28–14.59, P < 0.001) and older age (adjusted HR 1.09, 1.06–1.13, P < 0.001). Patients on haemodialysis had a cumulative risk of mortality of 24.5% (95% CI 14.0–40.8) at 1 year.

Conclusion: There is a high risk of mortality associated with DFI, substantially increased in patients undergoing haemodialysis, highlighting the importance of early and dedicated interventions targeted at this high-risk group.