The Mauritius and Rodrigues Non-Communicable Disease (NCD) Study

Mauritius and Rodrigues are islands in the south-eastern part of the Indian Ocean. Major changes in lifestyle have been seen during the last fifty years, including less physical activity and introduction of a westernised diet. In parallel, the disease panorama has changed from high infant mortality and infectious diseases to lifestyle-related diseases such as cardiovascular disease and type 2 diabetes.

The population in Mauritius are descendants to immigrants from South Asia, Africa and China, i.e., approximately 60% of the world population are represented. Mauritius is probably the only developing country that has followed the development of non-communicable diseases (NCD) and associated risk factors over a long time-period and continues to do so.

In the mid-eighties, the Mauritian government initiated a study on the prevalence of type 2 diabetes and cardiovascular disease, in collaboration with WHO and international experts. Altogether seven population-based surveys have been performed between 1987 and 2021, and approximately 39 000 (!) examinations have been recorded. The intention is to repeat the survey every fifth year.

The ethnicities of the participants have been 71% South Asians (India/Pakistan), 24% Creoles (Africa) and 5% Chinese, which reflects well the ethnical distribution of the population. Previous participants were followed up in 2007 and 92% were successfully traced. Studies have also been performed on the neighbouring island Rodrigues where the majority of the population are Creoles. During the follow-up survey in 2010, 97% of the 9 700 participants were traced.

At each survey, information was given and an individual consent form was signed. See attached the local (in Mauritius) ethical approval and consent form from the Mauritius survey 2021.

At each survey, participants were interviewed about living conditions, lifestyle and health, and anthropometry and blood pressure were measured. Biochemistry including lipids and an oral glucose tolerance test (OGTT) were performed Altogether approximately 28 000 electrocardiograms (ECG) were recorded in participants aged 35 years and older, all of which have been coded in Kaunas, Lithuania for signs of ischemic heart disease (Minnesota criteria) and myocardial hypertrophy.

The Mauritius NCD study was initially administrated by the International Diabetes Institute in Melbourne, Australia under the leadership of Professor Paul Zimmet together with Professor Jaakko Tuomilehto (Finland) and Professor George Alberti (United Kingdom). Today, the study is administrated and financed by the Ministry of health in Mauritius under the leadership of Doctor Sudhir Kowlessur.

Professor Stefan Söderberg at the Department of Public Health and Clinical Medicine, Umeå University, Sweden was introduced to the Mauritius NCD study during his postdoc (2001-2002) in Professor Zimmet's research team at IDI in Melbourne. Söderberg has since then continued to assist in the performance of the surveys and to analyse data. Today, Umeå university and the Department of Public Health and Clinical medicine have been granted the privilege to curate and analyse data generated in the Mauritius and Rodrigues NCD study.

Each survey has been evaluated and approved by the local ethics committee in Mauritius (see attached the approval from 2021). Analysing data in Sweden has been approved by the Swedish Ethical Authority (2023-07199-01).

In short:

Inclusion

• Men and women
• Randomly selected population-based samples (details see below)
• Target age from 25 to 74 years Exclusion
• Not living in the study area
• Age outside the age-range

In detail:

Inclusion criteria

In 1987, 10 randomly selected (with probability proportional to size) population clusters and a purposely selected area of Chinatown in the capital, Port Louis, were surveyed (age range 25-74), and all eligible residents were invited to participate.2 In 1992 and 1998, the same clusters were resurveyed as well as an additional three clusters selected to assess if trends in disease and risk factor distribution observed in the study cohort also occurred in independent clusters (age range 25 years and older). In 1998, the Chinatown cluster was not surveyed. Altogether, 9,559 individuals participated in the first three surveys and 60% of participants took part in more than one survey.

In 2004, a new study was performed, with similar methodology. In 2009, nine index clusters were chosen with one randomly selected from each of the nine districts in Mauritius. Then, two neighbouring clusters were chosen surrounding the index cluster to form a "super cluster." From this super cluster, one in three households was randomly selected and one adult per household was invited to participate.5 The same methodology was used in 2015 and in 2021 with new randomly chosen clusters forming "super cluster" as in 2009. In addition, a random sample from the 1998 survey was invited for a resurvey in 2015.

Participation rate has been over 85% in each survey. No sampling weights were used.

Same methodology was used in Rodrigues.

Exclusion criteria

Outside age-range and not being randomly selected.