Prévalence de l’hypertension artérielle et facteurs de risque associés : étude transversale à Mahajanga (Madagascar).

 

 

NA RANDRIAMIHANGY¹, SR RAKOTONDRASOA², B RAMILITIANA³, LR RAMIANDRISOA⁴, AF RAHERISON¹, D HARIBENJA RASOAVOLOLONA⁵, AHN RAKOTOARISOA⁶, F RALISON⁵, N RABEARIVONY⁴, S RAKOTOARIMANANA⁷

 

 

SUMMARY

 

 

Introduction: The objective of this study was to determine the prevalence of arterial hypertension and its risk factors in the city of Mahajanga, Madagascar.

Materials and methods: We conducted a descriptive and analytical cross-sectional study from October to December 2018. Depending on the participant's blood pressure, one or two home visits were made. Three situations helped confirm hypertension: blood pressure (BP) > 180/110 mmHg in a single visit, BP ≥ 140/90 mmHg confirmed at the second visit or the patient following antihypertensive treatment.

 

Results: We retained 400 participants with an average age of 42.4 ± 16.1 years of whom 64.5% were female. The prevalence of hypertension was 26.8% at the first visit. After the second visit, the prevalence was 23.3%. Seventy seven point four percent of the hypertensives were already aware of their arterial hypertension. Among known hypertensives, 23.6% were taking antihypertensive treatment and 47.1% of the treated hypertensives had normal blood pressure. Regarding the univariate analyses, advanced age groups, number of children greater than 3, history of smoking, overweight, obesity and abdominal obesity were significantly associated with hypertension. After the multivariate analyses, the risk factors retained were the advanced age groups compared to that of 18-34 years, the history of smoking, overweight and obesity.

Conclusion: The prevalence of hypertension in Mahajanga in the present study was almost the same as that of other cities in Madagascar. The risk factors we found out are well known in the literature. Informing the population on hypertension and its treatments still need to be improved.

 

 

KEY WORDS

Epidemiology, hypertension, prevalence, risk factors.

 

 

RESUME

 

Introduction : L’objectif de cette étude était de déterminer la prévalence de l’hypertension artérielle (HTA) et ses facteurs de risque  dans la ville de Mahajanga, Madagascar.

Matériels et méthodes : Nous avons mené une étude transversale descriptive et analytique d’octobre à décembre 2018. En fonction de la pression artérielle du participant, une ou deux visites à domicile étaient réalisées. Trois situations permettaient chacune d’affirmer l’HTA : pression artérielle (PA) > 180/110 mmHg en une seule visite, PA ≥ 140/90 mmHg confirmée à la deuxième visite ou prise de traitement antihypertenseur.

Résultats : Nous avons retenu 400 participants avec un âge moyen de 42,4 ± 16,1 ans  et une prédominance féminine (64,5%). La prévalence de l’HTA était de 26,8% à la première visite. Après la deuxième visite, la prévalence retenue était de 23,3%. Soixante-dix-sept virgule quatre pourcent des hypertendus étaient déjà au courant de leur HTA. Parmi les hypertendus connus, 23,6% prenaient un traitement antihypertenseur et 47,1% des hypertendus traités  avaient une pression artérielle normalisée. Sur les analyses univariées, les tranches d’âges avancés, le nombre d’enfants à la charge supérieur à 3, l’antécédent de tabagisme, le surpoids, l’obésité et l’obésité abdominale étaient significativement associés à l’HTA. Après l’analyse multivariée, les facteurs de risque retenus étaient les tranches d’âges avancés par rapport à celle des 18-34 ans, l’antécédent de tabagisme, le surpoids et l’obésité.

Conclusion : La prévalence de l’HTA à Mahajanga dans la présente étude était proche de celles des autres villes de Madagascar. Les facteurs de risque trouvés sont bien connus dans la littérature. L’information de la population sur l’hypertension artérielle et sa prise en charge restent à  améliorer.

 

 

MOTS CLES

Epidémiologie, facteurs de risque, hypertension artérielle, prévalence.

 

 

1. Department of Cardiology, University hospital of Mahavoky Atsimo, University of Mahajanga, Madagascar

2. National Institute of Public and Community Health (INSPC), University of Antananarivo, Madagascar

3. Department of Nephrology, University hospital of Joseph Raseta Befelatanana, University of Antananarivo, Madagascar

4. Department of Cardiology, University hospital of Joseph Raseta Befelatanana, University of Antananarivo, Madagascar

5. Department of Internal Medicine, University hospital of Mahavoky Atsimo, University of Mahajanga, Madagascar

6. Department of ENT, University hospital of Place Kabary, Université of Antsiranana, Madagascar

7. Intensive Cardiological Care Unit, University hospital of Joseph Raseta Befelatanana, University of Antananarivo, Madagascar.

 

 

Adresse pour correspondance

Narindrarimanana Avisoa Randriamihangy

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Tel. : +261 34 11 021 42

 

 

INTRODUCTION

 

 

Systemic arterial hypertension (referred to as hypertension) is currently among the most common cardiovascular risk factors. It constitutes a global public health problem because of its frequency and its complications such as heart disease, stroke, kidney failure, and premature mortality and disability [1–5]. Hypertension affects about one billion people worldwide, approximately one in four adults [1,2]. However, in many individuals, hypertension and its complications can be prevented. Prevention is far less costly, and its importance is even more significant in low-income countries like Madagascar. Many hypertensive people go undiagnosed because this disease is asymptomatic in its early stages. Moreover, those diagnosed may not have well-controlled hypertension. Prevention includes early detection, adequate treatment, and the control of risk factors for hypertension and cardiovascular diseases [1]. Thus, data on these epidemiological aspects of hypertension allow better curative and preventive care. Given that the literature on hypertension in Mahajanga is scarce, we aimed to determine its prevalence by using the definitions of the World Health Organization and the European Society of Hypertension as blood pressure (BP) ≥ 140/90 mmHg [1,6] along with its risk factors.

 

 

MATERIALS AND METHODS

 

 

Study setting

 

The study took place in the city of Mahajanga (Mahajanga I), a coastal area in northwestern Madagascar. It is located at 568 kms away from Antananarivo, the capital city. Mahajanga is the capital of the Boeny Region. The city is bounded to the south by the Bombetoka Bay, to the west by the Mozambique Channel, to the north and the east by the Mahajanga II district. It covers approximately 57 km². Mahajanga I has 26 Fokontany (the smallest territorial and administrative unit which constitutes cities in Madagascar). According to the INSTAT (Institut National de la Statistique or National Institute of Statistics), in the report of the Third General Census of Population and Housing (RGPH-3), the city of Mahajanga  had 68,470 households and 244,722 inhabitants in 2018 [7].

 

Study design and selection criteria

 

We carried out a descriptive and analytical cross-sectional study over three months (from October to December 2018). The target population consisted of the inhabitants of Mahajanga who were aged 18 and beyond. A medical resident collected data during household visits. We selected the households randomly until we reached the required number of participants in each Fokontany. We drew one participant per household. We did not include pregnant and lactating women. We excluded individuals who did not participate appropriately until the end of the data collection.

 

Sample size

The following formula gave us the sample size (N):

As we did not have any previous prevalence rate of hypertension in Mahajanga, we set it at the maximum value of p = 50%. With a confidence interval of 95% (Z = 1,96) and a margin  error of m = 5%, the minimum sample size was N = 384. We distributed the sample to all 26 Fokontany in the area of study. We calculated the number of participants per Fokontany in proportion to the number of the population in each Fokontany (Fig. 1).

 

Blood pressure measurements

 

The medical resident used an LD –579 SCIAN automatic device. According to the blood pressure (BP) of the participant, the study required only one or two home visits. The medical resident took the first series of three measurements during the first contact. When the measurements showed BP ≥ 140/90 mmHg but <180/110 mmHg, he carried out a second series of measurements a month later during the second visit. During each series of measurements, he checked the BP at the 5th, 10th and 15th minutes of rest in a seated position. He took measurements on both arms first, and afterwards on the arm with the highest BP. For the participants whom we only saw once (with a normal BP at the first visit or hypertension already known and treated), we obtained the blood pressure figures by calculating the average of the two last measurements (at the 10th and 15th minutes of rest). For the participants we visited a second time, we used the averages of the two last measurements made during the second visit.

 

Definition of hypertension

 

According to the World Health Organization and the European Society of Hypertension definitions, we considered a hypertensive participant a patient presenting one of the following criteria: hypertension already treated with one or more antihypertensive drugs, BP ≥ 140/90 mmHg at the first visit and confirmed during the second one or BP ≥ 180/110 mmHg at the first visit alone [1,6].

 

Definitions of other variables

 

A statement from the participant gave us information about the awareness and treatment of hypertension. We defined the control of hypertension under treatment by BP ≤ 140/90 mmHg. We measured the waist circumference in the navel in cms with a measuring tape touching the skin in a standing position. We defined abdominal obesity as waist circumference ≥ 94 cm for men and ≥ 80 cm for women [8, 9]. We measured the weight with a mechanical GIMA® scale. We obtained the body mass index (BMI) by dividing the weight (in kg) by the square of the height (in m²). We defined overweight by a BMI ≥ 25 kg / m², and obesity a BMI ≥ 30 kg/m². We collected  data regarding the  age, marital status, level of education, the number of dependent children, the history of smoking, physical activity, practice and duration of a nap as well as sleep based on statements from the participant. We considered any current or former smoker to have a history of smoking. Finally, we defined the practice of physical activity as a regular physical activity lasting 90 min or more per week (30 min x 3).

 

Ethical considerations

 

The methods abide by the Declaration of Helsinki. All precautions were taken to protect the confidentiality of personal information concerning the participant. We neither collected samples nor performed any invasive procedures on the participants. We obtained authorization from all the chiefs of Fokontany. Furthermore, we obtained informed consent from each person who took part in the investigation after explaining to him/her the objective and the course of the study. Each participant was free to withdraw from the study at any stage. We started free treatment with amlodipine for those in need during the first ten days. We also referred them to a physician or the hospital for further treatment.

 

Statistical analysis

 

We carried out data analysis with the Ri386® software version 3.6.3 / RStudio® software version 1.1.463. For quantitative variables, we calculated their central (mean) and dispersion parameters (standard deviation, range). For the qualitative variables, we calculated their proportions or rates. We used univariate and multivariate logistic regression to assess hypertension risk factors. The adjusted odds ratio (AOR) with its 95% confidence interval, as well as the p-value, were the main measures of association. The condition for integrating a variable in multivariate analysis was represented by a p-value < 0.25. For the multivariate analysis, the significance level was fixed at p < 0.05.

 

 

 

RESULTS

 

 

During the investigation, the medical resident approached 401 individuals. An individual did not participate appropriately until the end of the data collection. Hence, we retained 400 participants. The response rate was 99.75%. The average age was 42.4 ± 16.1 years (18-80 years) with 64.5% women (n = 258) and a sex ratio of 0.55. Fig. 1 shows the distribution of the participants in the 26 Fokontany. Table 1 shows the characteristics of these participants, along with the prevalence of hypertension in the subgroups. Women represented 70% (n = 105) of the participants aged 18 to 34, and 64.8% (n = 81) of participants aged 35 to 51 (Table 2).

The overall prevalence of hypertension was 26.8% (n = 107) during the first visits. After the second visits, the prevalence was 23.3% (n = 93). Seventy-seven point four percent (n = 72 of 93) of the hypertensive participants were already aware of their hypertension. Among the latter 23.6% (n = 17 of 72) were taking antihypertensive therapy and only 47.1% (n = 8 of 17) of them had controlled hypertension or BP ≤ 140/90 mmHg (Fig. 2).

By determining the risk factors for hypertension, with the logistic regression, in univariate analysis, we found significant associations between hypertension and the following: advanced age, history of smoking, overweight, obesity, and abdominal obesity. With the multivariate analysis, we found out that advanced age, smoking history and obesity were independent predictors of hypertension (Table 3).

 

 

DISCUSSION

 

 

Prevalence of hypertension

 

In order to optimize the reliability of the prevalence of hypertension, we carried out a second visit for participants with a high BP but less than 180/111 mmHg. According to the guidelines, the higher the number of the measurements and consultations, the more reliable were the diagnosis. Therefore, at least two measurements on at least two occasions were necessary to assess BP [3,6,10]. However, the gold standard diagnostic confirmation of hypertension currently relies on self-measurement and ambulatory blood pressure monitoring or ABPM, particularly when white coat hypertension or masked hypertension are suspected [2,6,10]. The prevalence of hypertension we found after the second visits (23.3%) decreased compared to the one obtained after the first visits (26.8%). We retain the last result of 23.3% as the prevalence of hypertension in the present study because this prevalence was obtained with a higher number of measurements and visits. However, the comparison with the prevalence of hypertension in other studies will be made with the prevalence of 26.8%. Indeed, the other authors reported that the prevalence of hypertension with a single series of measurements were carried out on only one occasion [11–25].

Prevalences higher than what we have in the present study have been reported in high income countries such as 29.0%, 30.41% or even 40.2% in China [11–13], 32% in the United States [3], 32.3% in France [14], 31.46% in Luxembourg [26] or from 29.3% to 36.8% in Italy [27]. Compared to these countries, the relatively low prevalence of hypertension in Mahajanga, as a city in a low-income country, is consistent with the literature [5,15,28]. Nevertheless, the prevalence of hypertension in our study is also lower than that of less wealthy countries and cities. A meta-analysis carried out in 2015 estimated the overall prevalence of hypertension by 32.3% in 45 low and middle-income countries and 31.1% in Sub-Saharan Africa [5]. It was estimated at 30.8% in 2010, in urban and rural African populations by recruiting even the youngest from 15 [29]. Indeed, higher prevalence rates than ours were reported in Cameroon (31.1%) [16], in Senegal (31.4%-46%) [17,30] or in Lome (36,7%) [18]. In addition to the lifestyle linked to the low socio-economic level and the lesser degree of urbanization in Mahajanga, other factors are probably involved, such as the female predominance of our sample. This female predominance was more noticed among the youngest (Table 2). Among the young and middle-aged adults, hypertension and cardiovascular disease are less common in women who are relatively protected by their sex hormones. From menopause, the difference between men and women tends to reverse [5,31,32]. The characteristics of the Malagasy population [7] and that of the sampling explain the predominance of women in our study. When we carried out the study by conducting home visits, housewives were the most available to participate.

Lower hypertension prevalence rates were reported in Madagascar: 22.18% of adults (18 and above) in Antsirabe in 2001 [19], 24.29% in Antananarivo and 11.06% in Toliara among 25 years old and beyond among residents in 2005 [20]. Several factors could explain the difference, such as the characteristics of the population or geographic differences. Nevertheless, these other malagasy studies were also carried out many years before the present one while the prevalence of hypertension tends to increase in low-income countries [33–35] and generally in Africa [29]. The prevalence of hypertension in developing countries was lower but was almost the same as that of developed countries [28,33]. There is even a tendency to the reversal of the prevalence rates between high income and low income countries [33]. Indeed, in more recent malagasy studies, the prevalence of hypertension were close to ours, even slightly higher. In 2009, it was 28.05% in the primary healthcare facilities of Antananarivo among adults aged 18 and beyond [21]. In 2013 and 2014, the prevalence of hypertension was of 27.0% in the rural areas of Moramanga, and 29.7% in urban areas among residents aged 15 years and beyond [22]. In Mandena in the SAVA region (north of Madagascar), in 2015-2017, it was of 26%, according to the definition of hypertension as BP ≥ 140 / 90 mmHg [23].

On the one hand, despite some methodological differences, the prevalence of hypertension found in the present study was broadly similar to the most recent prevalence in other cities of Madagascar. On the other hand, these recent prevalence like ours are higher than that of the early 2000s [19,20]. Even if there has not been any study in the same population to assess possible changes, there may be likely an increase in the urban prevalence of hypertension in Madagascar. Such an increase could be linked to many factors such as the increasing urbanization, the increase of the population [7] and more sedentary lifestyle, a more industrial diet and fast foods promoting salt consumption and fat, or the increased level of stress the population experienced. This phenomenon is partly responsible for the increase in morbidity and mortality linked to non-communicable diseases worldwide [5,36,37].

This probable trend towards an increase in the prevalence of hypertension should prompt us to take collective preventive measures. However, to have more accurate and general estimates, we should determine and regularly monitor the national prevalence of hypertension on adequately representative samples.

 

Risk factors for hypertension

 

The following risk factors for hypertension we observed in the present study are well known in the literature: advanced age [5,16,24,25,38–43], history of smoking [5,41,43,44] and obesity [5,8,16–18,25,41–52]. On the one hand, several pathophysiological factors explain the role of advanced age: the decrease in compliance of proximal arteries (due to arteriosclerosis and calcifications), the increase in the peripheral vascular resistance of small vessels, the decrease in sensitivity of baroreceptors, the increase in the reactivity of the sympathetic system, renal impairment, sodium retention, and the disruption of the renin-aldosterone relationship [38,53,54]. Tobacco, on the other hand, modifies blood pressure by accelerating arterial ageing, which is responsible for increased rigidity. Moreover, it does so by acting on the sympathetic system with direct consequences on BP, on lipid metabolism and insulin resistance, involved in the atheromatous disease [55]. In obesity, particularly visceral obesity, several mechanisms contributes to the elevation of blood pressure: hyperactivation of the renin-angiotensin-aldosterone system and the sympathetic system, oxidative stress, inflammatory syndrome, vascular lesions, insulin resistance, the disruption of renal structures and functions [56–60]. However, in the present study, we did not retain abdominal obesity after adjustment (multivariate analysis), even if its association with hypertension was significant in the univariate analysis. One explanation could be related to the definition that we used. Indeed, because of the lack of consensus on the definition of abdominal obesity for Malagasy people, we adopted the waist circumference from 94 cm for men and 80 cm for women, a definition that the International Diabetes Federation and the World Health Organization propose [8,9]. However, the definition of abdominal obesity is a subject of debate and would depend on ethnic origins [8,61–63]. This underlines the importance of determining the appropriate cut-off for Malagasy people.

Regarding the level of education, another malagasy study carried out in Antananarivo [40] reports that the prevalence of hypertension decreased with the level of education and income, like in other countries [5,16]. In the present study, even if the difference was not statistically significant, we observed hypertension in only 12.7% of those at the university level of the participant vs 23.5% to 30.4% of those at the lower levels (Table 1). University levels probably allow a better understanding of protective lifestyle measures.

The association of hypertension with physical exercise was not significant in Mahajanga, whereas this type of activity is considered to be a protective factor against hypertension and its inadequacy constitutes a risk factor [26,46,47]. In our study, we defined sufficient physical exercise based on the statement of the participant regarding his/her physical activities of more than 30 minutes, three times a week. The answers to this question may be too subjective.

However, discussing risk factors will always present difficulties until all the factors are known and analyzed. In the present study, we did not study many other usual risk factors, such as those that require biological analysis (diabetes, metabolic syndrome, etc.) and lifestyle habits (alcohol drinking, salt consumption, etc.).

 

 

LIMITATIONS TO STUDY

First, the gold standard diagnosis of hypertension should be based ideally on a higher number of measurements by self-measurements or even with the monitoring of ambulatory blood pressure. However, these methods are not practical to assess the prevalence of hypertension on a large scale. An insufficient number of measurements can lead to an underestimation or overestimation of the prevalence of hypertension. Second, for the reasons mentioned in the discussion, the female dominance of our sample may have influenced the prevalence of hypertension. Indeed, among young and middle-aged adults, the prevalence of hypertension is generally lower among women than men. Third, the target population consisted of adults living in Mahajanga who were aged 18 and beyond. However, we did not have their number when the study was designed. Thus, we used the standard formula indicated in the materials and methods to calculate the sample size. The sample size is relatively small compared to that of other studies. The interpretation of our results should take this into account. This could be improved for future studies by using a formula with the number of adults in the city. Finally, we could not study all potential risk factors for hypertension.

 

 

CONCLUSION

 

 

The prevalence of hypertension in Mahajanga was almost the same as that of other cities in Madagascar. Although this prevalence was relatively low compared to that of most other countries, the situation always remains concerning given the severity of the complications    of    hypertension.    Moreover, awareness, treatment and control rates were low. The risk factors we found are well known in the literature. An increase in the prevalence of hypertension in Madagascar is likely, but its evaluation requires regular national studies. Such a study will help us strengthen primary and secondary preventions. We have to improve public information and education on hypertension and its management, treatment as well as the prevention of its risk factors.

 

 

Table 1

Characteristics of the participants with the proportions of hypertension

 

 

		Hypertension		Total n (%)
		No n (%)	Yes n (%)
Mean age ± SD (y)		38.3±14.9	55.8±12.1	42.4±16.1
Mean weight ± SD (kg)		58.8±12.3	66.0±12.3	60.5±12.7
Mean height ± SD (m)		159.8±7.6	159.7± 8.7	159.8±7.8
Mean BMI  ± SD (kg/m²)		23.1±4.7	25.9±5.0	23.7±4.9
Gender	Male	105 (73.9)	37 (26.1)	142 (35.5)
	Female	202 (78.3)	56 (21.7)	258 (64.5)
Age group (y)	18-34	144 (96.0)	6 (4.0)	150 (37.5)
	35-51	99 (79.2)	26 (20.8)	125 (31.2)
	52-68	52 (54.2)	44 (45.8)	96 (24.0)
	≥ 69	12 (41.4)	17 (58.6)	29 (7.2)
BMI ≥ 25  kg/m²	Yes	91 (63.2)	53 (36.8)	144 (36)
	No	216 (84.4)	40 (15.6)	256 (64)
BMI ≥ 30  kg/m²	Yes	29 (63.0)	17 (37.0)	46 (11.5)
	No	278 (78.5)	76 (21.5)	354 (88.5)
Abdominal obesity	Yes	117 (66.1)	60 (33.9)	177 (44.2)
	No	190 (85.2)	33 (14.8)	223 (55.8)
History of smoking	Yes	67 (63.8)	38 (36.2)	105 (26.2)
	No	240 (81.4)	55 (18.6)	295 (73.8)
Marital status	Lives alone	97 (74.6)	33 (25.4)	130 (32.5)
	Lives with partner	179 (75.2)	59 (24.8)	238 (59.5)
	Lives with parents	31 (96.9)	1 (3.1)	32 (8.0)
Educational level	Illiterate	7 (1.8)	3 (0.8)	10 (2.5)
	Primary school	48 (12.0)	21 (5.2)	69 (17.2)
	Middle School	118 (29.5)	39 (9.8)	157 (39.2)
	High school	65 (16.2)	20 (5.0)	85 (21.2)
	University	69 (17.2)	10 (2.5)	79 (19.8)
Nap duration	No nap	123 (80.4)	30 (19.6)	153 (38.3)
	< 1 h	76 (71.0)	31 (29.0)	107 (26.8)
	≥ 1 h	108 (77.1)	32 (22.9)	140 (35.0)
Sleep duration	< 7 h	71 (71.7)	28 (28.3)	99 (24.8)
	7 – 9 h	174 (77.7)	50 (22.3)	224 (56.0)
	> 9 h	62 (80.5)	15 (19.5)	77 (19.3)

    

 

                                            Fig. 1: Distribution of the 400 participants in the 26 Fokontany of ahajanga.

 

 Prevalence 1: The prevalence estimated during the first visits. Prevalence 2: the prevalence retained during the second visits. Awareness: the proportion of those who were aware of their hypertension among confirmed hypertensives. Treatment:  the proportion of those who were treated among the known hypertensives. Control: the proportion of those with blood pressure ≤ 140/90 mmHg among treated hypertensives.

Fig. 2: Characteristics of arterial hypertension in Mahajanga

 

 

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