Incidence, risk factors and sequelae of long/post-COVID in people with diabetes compared to people without diabetes in Germany (longcovid-diab): a study protocol

Background: Several studies have shown that people with diabetes are at higher risk of experiencing a severe course of COVID-19 infection. However, it remains unclear whether diabetes per se is a risk factor for the development of Long/Post-COVID. In addition, there is a lack of nationwide, population-based studies on the epidemiology of Long/Post-COVID in people with diabetes. The aim of this project is to analyze: (1) incidence and time trends of Long/Post-COVID in people with and without diabetes between 2021 and 2023 in Germany as well as potential risk factors; (2) mortality, any hospitalization and hospitalization due to acute myocardial infarction, stroke, amputation and diabetic foot syndrome (DFS) after a Long/Post-COVID diagnosis, including an analysis of potential risk factors. Methods: This study is planned as a non-interventional longitudinal observational study based on statutory health insurance (SHI) data in Germany. The data holder is the Health Data Lab (HDL: data pool of billing data for all persons with statutory health insurance). The incidence rates of Long/Post-COVID will be estimated separately in the populations with and without diabetes and compared as corresponding relative risk. Moreover, we will analyse age- and sex-standardized mortality and hospitalization rates within 12, 24, and 36 months after a Long/Post-COVID diagnosis in the years 2021 to 2024. Potential uncertainties in diagnosing Long/Post-COVID (e.g., underreporting) will be addressed in sensitivity analyses. Discussion: The expected results will have high potential for use in epidemiological research on Long/Post-COVID, including the identification of potential risk factors in people with diabetes. The findings will serve to provide optimized healthcare for Long/Post-COVID patients with diabetes. Trial registration The study has been registered in the German Clinical Trials Register with identifier DRKS00036279. Registration Date 15.05.2025.