Sampling technique
The sampling scheme employed was a multistage systematic sampling stratified by age group. Each sentinel site constituted a cluster and the health area, within which the district hospital was implanted, constituted the area frame. The households of the selected health area were considered the final sampling unit. A census had been conducted in the entire selected health areas, where the households in the study site had been enlisted and all adults aged 25 years and above registered. The total number of subjects within each age group was determined. This was used to calculate the percentage contribution of each age group to the total population. This population percentage for each age group was then used to determine the number of households which was needed to achieve the desired sample size for each age group. The number of households obtained for each age group was then divided by the number of subjects in each group to obtain the sampling interval. The first household was selected randomly and individual age group sampling intervals were then used to obtain the households from which all the subjects were obtained.
Evaluation
During household visits, data were collected on the demographics, lifestyles/core behavioural profile, anthropometric and biochemical measures for each eligible participant, by trained medical personnel following the steps 1, 2 and 3 of the WHO STEPS instrument (Version 1.3) for Non-Communicable Diseases and their risk factor surveillance. The main sections included a self-reported information questionnaire (step1), anthropometrical measurements (step2) and the biochemical measurements (step 3).
Questionnaire
Basic core, expanded and optional variables with regards to socio-economic and demographic data, diabetes and its risk factors (tobacco, dietary habits and physical activity) were self-reported by the subjects. The type of last educational institution attended was used, assigning four categories: none (attended no educational institution), primary (1–7 years of education), secondary (8–14 years of education), and university (>14 years of education). The classification used for smoking was non-smoker (has never smoked + ex-smoker) and smokers (current smokers); Fruits and vegetables: number of days eaten/week; physical activity: leisure time (standing or sitting for more than 10 minutes denoted as yes/no), moderate activity (days/ week and time spent on each activity), vigorous activity (days/week and time spent on each activity).
Anthropometric measurements
Physical measurements were height, weight, waist and hip circumference (HC), diastolic and systolic blood pressure and pulse rate. Height (cm) was measured to the nearest 0.5 centimeter (cm) using a portable stadiometer. Weight (kg) was measured to one decimal place, using Tatina electronic digital scale. Waist circumference (cm) was measured at the midpoint between the lower rip and the upper margin of the iliac crest, and hip circumference at the level of the greater trochanters was measured to the nearest millimeter using a flexible tape. BMI (kg/m2) was calculated using the averages of the height and weight, with the formulae: weight [kg]/ Height [m2]. Body fat distribution was evaluated by the WHR, by dividing WC by HC and WHtR, by dividing WC by height.
Three readings of blood pressure, at 5 minutes interval were taken from each participant. Measurements were taken on a sitting position after 10 minutes rest, following the American Heart Association (AHA) procedures, using electronic AND 078 Model UA-767 fully automatic, clinically validated digital BP monitor (A & D Company Limited Tokyo, Japan), Hypertension was defined as systolic BP (SBP) ≥ 140 mmHg and/or diastolic BP (DBP) ≥90 mmHg. Subjects with values of SBP and DBP under the defined limits but who reported taking antihypertensive treatment for at least two weeks before the survey onset were classified as hypertensive.
Diagnosis of diabetes
Fasting capillary glucose (FCG) was measured using the HemoCue® B-Glucose photometer (Ängelholm, Sweden) after an overnight fast. We used fasting capillary glucose with an abnormal FCG ≥ 110 mg/dl or 6.1 mmol/l FCG, to defined diabetes, together with ≥5.6 and <6.0 mmol/l to define impaired fasting capillary glycemia, as recommended by WHO. For every subject with an abnormal FCG (≥ 110 g/l or 6.1 mmol/l), an oral glucose tolerance test (2hPG 6.7-11.0 mmol/l) was done to confirm the diagnosis of diabetes and identify cases of impaired glucose tolerance (IGT) using the WHO Diagnostic Criteria