Incident diabetes within the first two years after SARS-CoV-2 infection: a population-based retrospective cohort study of the Agency for Health Protection of Milan, Italy.

BACKGROUND: Postacute sequelae of SARS-CoV-2 infection (PASC), including persistent symptoms and acute and chronic diagnoses, have become a major research focus. Diabetes mellitus, beyond its established link to COVID-19 severity, is increasingly recognized as a potential long-term outcome. This study investigated the association between SARS-CoV-2 infection and incident diabetes using population-level health administrative data (HAD) from the Agency for Health Protection of Milan, where the epicenter of the pandemic in Italy took place. METHODS: This retrospective cohort study included adult residents without a history of diabetes who underwent SARS-CoV-2 testing between 1 March and 31 December 2020. Test-positive individuals were matched 1:1 to test-negative individuals based on sex, age, and testing week. The cohort was followed through 31 December 2021. The incidence of diabetes, identified using an HAD-based case-detection algorithm, was compared between the two groups, and in stratified analyses by sex and age, using weighted Cox models adjusted for chronic comorbidities, area-level deprivation, influenza and pneumococcal vaccinations. Weights were calculated via the inverse probability weighting approach. Effect estimates are presented as hazard ratios (HRs). RESULTS: Our final cohort included 248,176 residents (124,026 test-negative, 124,150 test-positive). Over a median follow-up time of 415 days, 739 positive (0.60%) and 657 negative (0.53%) individuals were newly identified with diabetes. The incidence among positive individuals was 572.82 per 100,000 person-years (CI 531.52-614.12), and that among negative individuals was 509.50 per 100,000 person-years (CI 470.54-548.46). The overall HR was 1.13 (CI 1.02-1.25). In stratified analyses, this effect was prominent in women aged 41-60 years (HR 1.31; CI 1.02-1.68). CONCLUSIONS: This study provides population-based evidence supporting an association between SARS-CoV-2 infection and newly detected diabetes. These findings contribute to understanding the long-term health impact of COVID-19 and may inform public health strategies for PASC prevention and management.