Data collection and definition

The study is ancillary to a survey regarding the prevalence of epilepsy in the community of Ntoum, Gabon. Ntoum is a city with 8765 inhabitants, in the administrative region of the estuary, located in northeast Gabon. The population is mainly rural but also includes business and industry workers. Overall, 6259 subjects were included in the first survey and 736 in the ancillary study; subjects aged greater or equal to 40 years were included in the ancillary study. In the last census, subjects aged more than 40 years represented 14% of the Gabonese population .

Over a period of 12 days, a group of 46 field investigators visited all of the households in the area. A group of 10 guides accompanied the investigators. Each day, the investigators visited a district that had been previously determined; all of the residents had already been informed about the study. The investigators were trained by one of the authors (EN). All subjects aged more than 40 years were also asked to participate in the CVD survey; all participants gave their informed consent. Subjects were interviewed about their smoking status (non-smokers or ever smokers, including former or current smokers) and history of diabetes mellitus (DM), hypertension and dyslipidaemia. Health records and prescriptions were analysed. Participants reporting DM were asked about their use of insulin and oral medications. Participants reporting any use of lipid-lowering medication or anti-DM drugs were considered as dyslipidaemic or diabetic, respectively. The subjects were also asked about their history of documented stroke, heart or vascular disorders. Height and weight were measured with the participants being barefoot and wearing light clothing. Body mass index (BMI) was calculated as kg/m ² . A waist measurement was performed using a non-stretching tape with the subject in the standing position. Blood pressure was measured on both arms with a mercury manometer. Hypertension was defined either as the use of antihypertensive drugs or as resting arm systolic blood pressure greater or equal to 160 mmHg (participant sitting for 5 minutes). Lower limb peripheral pulses (posterior tibial and dorsalis pedis) were palpated in the same position. As the population is French speaking, French versions of the World Health Organization (WHO) Rose angina questionnaire and the Edinburgh claudication questionnaire (ECQ) for intermittent claudication were used .

Coronary artery disease (CAD) was defined as a history of CAD reported by the participant or a positive WHO Rose angina questionnaire. Cerebrovascular disease was defined as a report of a documented stroke or transient ischaemic attack. PAD was defined as a documented history of PAD, an absent posterior tibial pulse or a ‘positive’ or ‘possible’ ECQ (‘possible’ being defined as calf pain on walking but otherwise not fully concordant with the ECQ criteria) . Finally, an interarm systolic blood pressure difference greater than 15 mmHg defined the presence of subclavian stenosis, a condition recently found to be a marker of poorer CVD prognosis . The participants were considered as having CVD in case of any of the above-mentioned situations. In the absence of a specific ethical committee in this country, the survey was approved by the Ministry of Public Health and of Gabon.

Statistical methods

Data are reported as mean ± standard deviation. Categorical data are presented as percentages with 95% confidence intervals (CIs) when appropriate. Comparisons within groups were made using the Chi ² test for categorical variables and Student’s t test for continuous variables. To assess the association between CVD and the risk factors, a multiple logistic regression analysis was used to determine the independent predictive factors, using a backward stepwise method. A P value < 0.05 was fixed for statistical significance. Statistical analyses were performed using Statview 5.0 software (SAS Institute, Cary, NC, USA).