Retrospective observational study of Italian patients with diabetes mellitus in Covid-19 era: a big data approach

Background: Diabetes mellitus (DM) prevalence in patients with severe acute respiratory coronavirus virus (SARS-CoV-2) infection differs among studies, although pre-existing DM seems to double the risk of critical infection and mortality. Objectives: To evaluate incidence and mortality risk of SARS-CoV-2 infection in a large diabetic population in Northern Italy in pre-vaccine era. Methods: Retrospective, observational, big data study including non-vaccinated subjects with type 1 and type 2 DM in the Province of Modena, submitted to at least 1 swab for SARS-CoV-2 between March 2020 and March 2021. Results: SARS-CoV-2 infection was detected in 2302 of 9553 diabetic patients (24.1%) with death in 8.9% of cases. No difference in SARS-CoV-2 prevalence was detected considering sex, whereas youngest people showed highest SARS-CoV-2 infection rate. DM duration was shorter in infected than uninfected patients (P < 0.001), but HbA1c was higher in infected compared to uninfected patients (P < 0.001). Accordingly, SARS-CoV-2 was less frequent in patients treated with anti-diabetic drugs compared to those not treated (P < 0.001). SARS-CoV-2 infection was predicted by age (OR 1.013, 95%CI:1.008-1.017), DM duration (OR 1.007, 95%CI:1.001-1.013), and HbA1c (OR 1.009, 95%CI:1.002-1.016). COVID-19 mortality was predicted by DM duration (OR 1.010, 95%CI: 1.005-1.015) and HbA1c (OR 1.005, 95%CI:1.002-1.009). At ROC analyses with death as test variable, worse prognosis was predicted by DM duration longer than 10.9 years (AUC=0.639, 95%CI:0.601–0.676) and age older than 74.4 years (AUC=0.797, 95%CI:0.767–0.827). Conclusion: Our study confirms the correlation between SARS-CoV-2 related mortality and DM. Although SARS-CoV-2 infection was more frequent in the younger patients, a poor glycemic control worsens outcomes, especially in older diabetic people with long DM duration. Patients with DM and SARS-CoV-2 should be followed carefully when older than 74 years and with long DM duration.