Epidemiology of hypertension and other cardiovascular disease risk factors in the urban population of Soussa, Tunisia

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H. Ghannem  and A. Hadj Fredj

ABSTRACT: To illustrate the distribution of hypertension in the community, an epidemiological survey was conducted based on a representative sample of 957 adults aged ≥ 20 years resident in Soussa, Tunisia in 1995. The prevalence of hypertension according to the new World Health Organization criteria (systolic blood pressure >140 mmHg and/or diastolic blood pressure >90 mmHg) was 28.9%. Hypertension was significantly higher in cases with obesity, android obesity and for persons aged >40 years. History of diabetes was found in 10.2% of cases, obesity in 27.7%, overweight in 56.7%, android obesity in 36.0% and smoking in 61.4% of men and 4.2% of women.

Epidémiologie de l'hypertension et des autres facteurs de risque de maladies cardio-vasculaires dans la population urbaine de Sousse (Tunisie)

RESUME: Afin d'illustrer la distribution des cas d'hypertension dans la communauté, une enquête épidémiologique a été réalisée en 1995 sur la base d'un échantillon représentatif composé de 957 adultes âgés de 20 ans et plus et résidents à Sousse (Tunisie). La prévalence de l'hypertension selon les nouveaux critères de l'Organisation mondiale de la Santé (PAS > 140 mmHg et/ou PAD >90 mmHg) s'élevait à 28,9%. L'hypertension était considérablement plus élevée dans les cas associés à une obésité et une obésité androïde ainsi que chez les personnes âgées de plus de 40 ans. Des antécédents de diabète ont été trouvés dans 10,2% des cas, une obésité dans 27,7% des cas, une surcharge pondérale dans 56,7% des cas, une obésité androïde dans 36% des cas et le tabagisme dans 61,4% des cas chez les hommes et 4,2% chez les femmes.

Introduction

Hypertension is a major risk factor for cardiovascular diseases (CVD) [1,2] which are still the leading causes of death in European and North American societies [3,4] despite the downward trend observed during the past three decades [5-8]. Furthermore, hypertension is a very common disease and its prevalence varies greatly within and between countries [9-11].

The epidemiological transition being observed in developing countries [12], will lead to an increase in the prevalence of hypertension as a result of increased life expectancy and the stress of urbanization, which is growing rapidly in almost all developing countries [13].

In Tunisia, little is known about the hypertension distribution in the urban population; a few studies have been undertaken in rural or semiurban populations [14] or designed particulary to assess other CVD risk factors such as diabetes in the community [15].

In order to assess the magnitude of the problem of hypertension in the community and to establish a CVD risk-factor profile, we undertook an epidemiological survey in the urban population of Soussa as the first step of a comprehensive control programme of chronic diseases.

Subjects and methods

The study population was composed of adults aged 20 years and over who were resident in the city of Soussa during the year 1995/1996. We used a two-stage cluster sampling using the lists of districts and households of Soussa given by the 1994 Census. The sample size required (n = 1225) was calculated according to an estimated prevalence of hypertension of 15% [13], with a precision of 2% and a confidence level of 95%. The sample size corresponded approximately to 409 households if we considered an average of three persons aged ≥ 20 years per household. We added about 60 households to compensate for any refusal to participate, anticipated to be around 10%-15%. The sampling of 465 households was systematic (1/4) from the list of districts already chosen systematically (1/15) in the city of Soussa and was done by the Regional Office of the Tunisan National Institute of Statistics. The survey was carried out in Soussa from September to November 1995.

The study team was composed of a social worker to sensitize people to the aims of the study and to encourage their participation, two physicians for the physical examination and a dietician to assess food consumption by a 24-hour recall and frequency questionnaire. The study variables in the questionnaire included sociodemographic data, medical history, dietary habits, drinking and smoking habits, and data from the physical examination. Measurement of blood pressure was done using an auto-inflate digital electronic monitor (Spengler, Mistral). The first measurement was taken after a 15-minute rest in a sitting position and was followed by two subsequent measurements in the middle and at the end of the interview. The average of the three measurements was used to assess the presence or absence of hypertension according to two criteria (systolic blood pressure ≥ 160 mmHg and/or diastolic blood pressure ≥ 95 mmHg and systolic blood pressure ≥ 140 mmgHg and/ or diastolic blood pressure ≥ 90 mmHg). Those with high blood pressure were referred to ambulatory clinics for confirmation of the diagnosis. Diabetes was assessed according to a previous medical history of diabetes; serum lipids were not measured in this study. Weight was measured bare-foot and expressed in kilograms (kg) and the height expressed in centimetres; waist and hip measurements were also expressed in centimetres. The body mass index (BMI) (kg/m²) was used to define obesity (BMI >30 kg/m²), overweight (BMI >25 kg/m²) and the waist to hip ratio (WHR) was used to define android obesity (WHR >0.9). Smoking was assessed using a set of questions about current and previous tobacco consumption. Current smokers were those who smoked regularly and had smoked during the previous week of the study.

Data analysis was done by Systat (system for statistics, version 3). We used the chi-squared test, t-test and ANOVA for subgroup comparison, using the 5% level of significance.

Results

Among the 465 households sampled, 1346 persons were aged ≥ 20 years. Women represented 52. 8% and men 47.2% of the total sample size. We examined 957 persons with an overall participation rate of 71.1%. Table 1 gives the sample size, the number of people examined by age and sex and the participation rate by sex.

Of the people examined, 180 had blood pressure levels of 160/95 or higher. The prevalence of hypertension, as defined by the cut-off points 160/95, was 18.8% (Table 2). There was no statistically significant difference between men (18.6%) and women (18.9% ) (χ2 = 0.004, P = 0.95). The age adjusted prevalence for the whole Tunisian population (≥ 20 years) was 15.6%. Prevalence of hypertension increased with age from 3.2% for 20-30 year olds to 41.0% for those over 70 years. This trend was statistically significant (χ2 = 115.42, P < 0.000001). According to the criterion blood pressure 140/90, the prevalence of hypertension was 28.9% with no statistical difference between men (30.0%) and women (28.4%) (Table 2).

The prevalence of hypertension was significantly higher in people aged 40 years and over, people with obesity, people with android obesity and for people with a history of diabetes (Table 3).

Before the age of 40 years, the mean systolic blood pressure was significantly higher for men (127.3 ± 13.7 mmHg) than for women (122.5 ±14.1 mmHg) (t = 3.28, P = 0.001). At or after the age of 40 years, women had a slightly higher mean systolic blood pressure (144.0 ± 19.1 mmHg) than men (142.2 ± 20.2 mmHg). This difference was not statistically significant (t = 0.939, P = 0.348). For diastolic blood pressure before 40 years, there was no statistically significant difference between men (75.8 ± 13.3 mmHg) and women (75.3 ± 12.4 mmHg). However, at or after 40 years, women had significantly higher diastolic blood pressure (86.3 ± 15.9 mmHg) than men (82.9±14.4 mmHg) (t = 2.25, P = 0.025) (Table 4).

The mean systolic and diastolic blood pressure increased with weight. The difference was statistically significant (Table 5). For people with android obesity, the mean systolic blood pressure was significantly higher (139.5 ± 20.3 mmHg) than for those with no android obesity (129.9 ± 18.3 mmHg) (t = 7.45, P < 0.0001). The mean diastolic blood pressure was also significantly higher in cases with android obesity (84.0 ± 15.8 mmHg versus 78.0 ± 13.6 mmHg) (t = 6.06, P < 0.0001).

History of diabetes was found in 10.2% of the study population. It was significantly higher for women (11.5%) than for men (7.2%) (P = 0.044) (Table 6). It was also higher in cases with obesity (17.0% versus 7.7%) (P < 0.0001) and in cases with android obesity (15.0% versus 7.5% ) (P < 0.0001).

Obesity (BMI ≥ 30 kg/m2) was found in 27.7% of the study population. It was significantly higher for women (34.3%) than for men (12.4%) (P < 0.00001) (Table 6). Overweight (BMI > 25 kg/m2) was found in 56.7% of the study population. Android obesity (WHR > 0.9) was found in 36.0% of the study population. It was significantly higher for men (49.7%) than for women (30.1%) (P < 0.00001) (Table 6).

Smoking was reported in 21.5% of the study population. It was significantly higher for men (61.4%) than for women (4.2%) (P < 0.000001) (Table 6).

Discussion

Hypertension is a major CVD risk factor, but there is a scarcity of data on its epidemiology in an urban population that is shifting from communicable to noncommunicable diseases. Urbanization is expected to raise the morbidity related to unhealthy lifestyles such as cardiovascular diseases and their risk factors [3,16].

The participation rate in this study (71.1%) was acceptable for a household survey, when people need to be at home to be examined. This explains why the participation rate was lower for men (45.7%) than for women (93.8%); men are more likely to work outside the home and are less able to take time off work in order to participate in a study. However, the sample examined was homogeneous for age group and sex (Table 1) and the distribution of those who were not examined was similar to that of those who participated in the study.

The study showed that the Tunisian urban population had a hypertension prevalence of 18.8% (criterion limit 160/95) or 28.0% (criterion limit 140/80). Hypertension prevalence was significantly higher for people with obesity and android obesity. In fact, there is overwhelming evidence that obesity and hypertension are linked [17-20]. The high level of obesity (27.7%) and android obesity (36.0%) found in our study might explain the high prevalence of hypertension. Furthermore, many screened hypertensive patients were unaware of their condition. This emphasizes the need for hypertension screening in primary health care, which is now very accessible in Tunisia, even in rural areas.

Since hypertension is a major risk factor for CVD, its control in the community should be integrated into a comprehensive preventive programme for CVD control, as has been done in countries with high CVD mortality [21,22]. The basic principle is that diseases with common risk factors require common preventive strategies. The preventive strategies should be based on a health education programme that promotes healthy lifestyles, by improvement of dietary habits, eradication of tobacco use, increased physical activity and alleviation of deleterious psychosocial factors related to cardiovascular disease [23,24].

The results of the present study indicate the need to plan and implement actions on prevention, detection and treatment of hypertension as a part of a comprehensive programme of CVD control in the community. Only a comprehensive strategy based upon the public health approach described in the Victoria Declaration [23] will we be able to stem the increasing prevalence of CVD risk factors in Tunisia.

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