Diabetes, one of the most prevalent chronic disease (~ 9% worldwide), represents a major public health burden in terms of morbidity, disability and mortality. Caring for patients with diabetes requires effective collaboration between healthcare providers, teamwork, self-management education and use of evidence-based medicine. However, these processes of care are complex and often suboptimal. Improving quality of diabetes care is thus needed to reduce the health and societal burden of this disease.

In the canton of Vaud, a state in Switzerland with more than 700,000 inhabitants, a recent population-based study has shown that the prevalence of diabetes was around 7%. Data on the quality of diabetes care is scarce and quality of care data are still infrequently and unsystematically collected in Switzerland. In addition, when data are available, they focus on intermediate outcomes as well as clinical and biological cardiovascular risk factors. Population-based data on patient-reported outcomes are not considered.

In 2010, the Public Health Department of the canton of Vaud initiated the development of a regional diabetes program entitled "Programme cantonal Diabète" (PcD). It aimed both at decreasing the incidence of diabetes and improving care for patients with diabetes.

To tailor the program to the healthcare needs of patients and healthcare professionals involved in diabetes care, an exploratory study using qualitative methods was conducted in 2010. This was followed by a population-based survey conducted in fall 2011 and summer 2012. The objectives of the survey were to characterize patients with diabetes and assess the quality of the care they received. In addition, the results of the survey were used to help targeting unmet needs and possible areas of improvements, and constituted the patients' baseline measurement for the evaluation of the PcD.

The CoDiab-VD cohort emerged from that initial project; its specific objectives were 1) to follow over time the quality of diabetes care, 2) to explore topics that the PcD needed for its development, 3) to assess the impact of the PcD on the care of patients with diabetes, and 4) to evaluate the coverage of the PcD in the canton of Vaud.

Diabetes, one of the most prevalent chronic disease (~ 9% worldwide), represents a major public health burden in terms of morbidity, disability and mortality. Caring for patients with diabetes requires effective collaboration between healthcare providers, teamwork, self-management education and use of evidence-based medicine. However, these processes of care are complex and often suboptimal. Improving quality of diabetes care is thus needed to reduce the health and societal burden of this disease.

In the canton of Vaud, a state in Switzerland with more than 700,000 inhabitants, a recent population-based study has shown that the prevalence of diabetes was around 7%. Data on the quality of diabetes care is scarce and quality of care data are still infrequently and unsystematically collected in Switzerland. In addition, when data are available, they focus on intermediate outcomes as well as clinical and biological cardiovascular risk factors. Population-based data on patient-reported outcomes are not considered.

In 2010, the Public Health Department of the canton of Vaud initiated the development of a regional diabetes program entitled "Programme cantonal Diabète" (PcD). It aimed both at decreasing the incidence of diabetes and improving care for patients with diabetes.

To tailor the program to the healthcare needs of patients and healthcare professionals involved in diabetes care, an exploratory study using qualitative methods was conducted in 2010. This was followed by a population-based survey conducted in fall 2011 and summer 2012. The objectives of the survey were to characterize patients with diabetes and assess the quality of the care they received. In addition, the results of the survey were used to help targeting unmet needs and possible areas of improvements, and constituted the patients' baseline measurement for the evaluation of the PcD.

The CoDiab-VD cohort emerged from that initial project; its specific objectives were 1) to follow over time the quality of diabetes care, 2) to explore topics that the PcD needed for its development, 3) to assess the impact of the PcD on the care of patients with diabetes, and 4) to evaluate the coverage of the PcD in the canton of Vaud.

Patients with diabetes were recruited by community-based pharmacies in the fall of 2011 and the summer of 2012. Participating community-based pharmacies, randomly contacted among those registered in the canton of Vaud, were asked to recruit non-institutionalized adult patients with diabetes (disease duration of at least 12 months), who were visiting the pharmacy with a prescription for oral antidiabetic drugs, insulin, glycemic strips or glucose meter.

At baseline, patients filled in a self-reported paper questionnaire that targeted the following areas:

• diabetes characteristics (type, disease duration, treatment, complications)
• receipt of diabetes care: recommended process of care indicators (such as annual eye examination by ophthalmologist, foot examination, microalbuminuria…) , and specific outcomes of care (such as HbA1C levels, generic and specific (health-related) quality of life (SF-12 and ADDQoL))
• congruence of care with the chronic care model (PACIC)
• healthcare utilization
• health behaviors (smoking and drinking habits, physical activity) and health status (comorbidities)
• self-management support (for example glycemic self-monitoring, self-efficacy, information level about diabetes)
• sociodemographic characteristics (age, gender, nationality, place of residence, education, employment, marital status, family size, family income, insurance status).

Participants were also asked to give the contact details of their family doctor and/or diabetologist. With the consent of the patients, treating physicians were contacted and were asked to fill a brief paper questionnaire requesting some clinical and laboratory data. Physicians were contacted in 2011, 2012 and 2014; physicians' follow-up was not repeated thereafter due to financial and logistic constraints.

Patients were contacted annually using paper follow-up questionnaires, consisting in a core set of questions similar to the baseline questionnaire. New questions were added and developed yearly according to the development and needs of the PcD. This allowed us to investigate these specific topics: diabetic foot in 2013; psychosocial outcomes related to diabetes and diabetes care in 2014; eyes and diabetes, as well as coordination and continuity of care in 2015; multimorbidity and needs for patient education in 2016; and pharmacy care in 2017.

A second recruitment, requested and financed by the funders, has been organized in 2017, in order to obtain a new population-based picture of diabetes in the canton of Vaud. It will allow 1) to compare data obtained at both recruitments, 2) to compare data obtained in 2017 from the second recruitment and from the annual follow-up of the first recruitment, and 3) to increase the number of patients with diabetes included in the CoDiab-VD cohort.

If requested by the PcD, additional follow-ups will take place in 2019 and in 2021.

Inclusion Criteria:

• Diagnosis of diabetes mellitus
• Disease ≥ 12 months
• Age ≥ 18 years
• Residing in the canton of Vaud, Switzerland, non-institutionalized
• Informed consent

Exclusion Criteria:

• Gestational diabetes mellitus
• Obvious cognitive impairment
• Not speaking or understanding French well enough

Non-institutionalized adult patients with diabetes (≥18 years, type 1 or 2 diabetes, disease duration ≥12 months) who were visiting the pharmacy with a prescription for oral antidiabetic drugs, insulin, glycemic strips or glucose meter, at the time of the recruitment, are eligible for this study.