The "CoDiaM study" examines how diabetes management and outcomes are changing during the COVID-19 pandemic and whether these changes are influenced by socio-demographic factors, health literacy, self-efficacy and perceived social support.

The Covid-19 pandemic created new challenges for patients with diabetes and their treating physicians. In order to protect people from SARS-COV-2 infections, social contacts were reduced by restrictions on many areas of social life. As a side effect, these measures could have also led to changes in the self-management of patients with diabetes mellitus, such as lack of physical exercise, less healthy dietary behavior, and a reduced intensity of medical care. These possible changes may be associated with poorer control of blood glucose, cholesterol, and blood pressure. Therefore, the CoDiaM study will investigate how management and outcomes of diabetes are changing during the pandemic and identify associated factors.

The study is based on data of patients treated in three GP practices specialized on diabetes treatment in Hamburg, Germany. Data collection will include a written patient survey and extraction of clinical data from patient records. The patient's survey includes sociodemographic data and validated instruments to assess diabetes self-management (DSMQ), health literacy (HLS-EU-Q16), self-efficacy (General Self-efficacy scale) and perceived social support (F-SozU K14). Data will be analyzed by descriptive statistics and multivariable, multilevel linear and logistic regression analyses adjusted for possible confounders and random effects on the practice level.

Inclusion Criteria:

• being 18 years or older, and
• having diabetes type 2 or type 1, and
• having consulted the practice at least once in 2019 AND at least once in 2020

Exclusion Criteria:

• no capacity to consent (e.g. because of dementia)
• insufficient German language skills to understand the questions in the questionnaire
• not able to fill out the questionnaire (e.g. because of blindness)
• gestational diabetes

The study is located in Hamburg, Germany. Patients from three GP practices specialized on diabetes treatment in Hamburg will be included. In each practice, eligible patients with diabetes type 1 and 2 will receive patient information, consent form and questionnaire by mail. After written informed consent and after the questionnaires have been returned, data from patient records in the practices will be extracted. The investigators estimated that approximately 3000 patients will be eligible to be contacted. From pretest and experience with similar studies the investigators anticipated a response rate of 25% (=750 patients).

Individual participant data are available from the principal investigator on reasonable request.