Hypertension prevalence, awareness, treatment and control in Dakar (Senegal)

Abstract

The prediction of risk profile trends associated with non-communicable diseases in developing countries is among the greatest global health challenges. The aim of this study is to estimate prevalence, awareness, treatment and control of hypertension in Dakar (Senegal). This study was carried out between January and June 2009 on a population sample of 600 individuals living in the department of Dakar. This sample was constructed using the quota method in order to strive for representativeness. Sociodemographic characteristics, hypertension, hypertension awareness, treatment and control, and body mass index of individuals were collected during face-to-face interviews. Statistical analyses used were χ²-tests and binary logistic regressions. Prevalence of hypertension was 27.50%. Prevalence of awareness, treatment and control among hypertensives were 27.88%, 16.97% and 5.45%, respectively. Logistic regression showed that the prevalence, awareness and treatment of hypertension increased with increasing age. Overweight and obese subjects were more often hypertensive but did not differ from others in awareness and treatment. This could be linked to the social valorization of stoutness in West Africa, which explains that excess weight is not perceived as a risk factor for hypertension. In conclusion, given the very low rates of awareness, treatment and control in our sample, developing strategies for averting a hypertension epidemic must be a priority objective.

Introduction

An epidemiological transition with the increasing prevalence of chronic non-communicable diseases (NCDs) is already underway in sub-Saharan Africa (SSA).^{1, 2, 3, 4, 5, 6, 7, 8} Consequently, in SSA, although the burden of infectious disease has fallen, changes in lifestyle and diet, and an increase in life expectancy have resulted in a greatly increased burden of NCDs.^{9, 10, 11}

The commonest NCDs experienced during the early stage of the epidemiological transition are hypertension^{4, 12, 13} and cerebral vascular accidents (strokes), with strokes in SSA mainly attributable to uncontrolled hypertension.^{6, 13, 14} In Senegal,¹⁵ as in other SSA countries, hypertension is rapidly becoming a major public health burden.^{16, 17, 18, 19, 20, 21}

However, in SSA, despite the increasing prevalence of hypertension, rates of awareness, treatment and control remain low.^{5, 22, 23, 24} Moreover, information on factors associated with awareness, treatment and control of hypertension is very scarce,² particularly in Senegal. However, it is difficult to reverse the underlying pathophysiology of hypertension once it has developed. To achieve a meaningful reduction in morbidity and mortality, knowledge of the prevalence of high blood pressure (BP) and the extent to which it is being detected, treated and controlled is essential.⁸

This study was undertaken to estimate prevalence, awareness, treatment and control of hypertension in Dakar (Senegal).

Materials and methods

Population sample

In order to carry out this study, a comprehensive survey was conducted from January to May 2009 in Dakar. In 2009, according to the Agence Nationale de la Statistique et de la Démographie du Sénégal, there was a total of 990 019 individuals in Dakar’s department.²⁵ The population sample selected for this study comprised 600 individuals of age 20 years and over. The sample was constructed using the combined quota method (cross-section by age, gender and town of residence) in order to strive for representativeness of the population of the department of Dakar, age 20 years and over. Data from the Agence Nationale de la Statistique et de la Démographie dating from the last census (2002) were used. The quota variables used were gender (male/female), age (20–29/30–39/40–49/50 years and over) and town of residence. The towns were grouped by the four arrondissements of the department of Dakar: Plateau-Gorée (five towns), Grand Dakar (six towns), Parcelles Assainies (four towns) and Almadies (four towns). Practically, this method requires constructing a sample that reflects the proportions observed in the general population; for example, according to the last census, in the town of Medina (Plateau-Gorée arrondissement) 2% of the population were men aged 20–29 years. The sample was constructed to match this proportion by including 12 men aged 20–29 years, living in this town. The method was the same for each quota by gender, age and town.

In each town, four investigators (PhD students in Medicine and Pharmacy) started out from different points each day to interview individuals in Wolof or French in every third home. Investigators had a certain number of individuals to interview (women aged 20–29 years/men aged 20–29 years/women aged 30–39 years/men aged 30–39 years/women aged 40–49 years/men aged 40–49 years/women aged 50 years and over/men aged 50 years and over, in each town) to meet the quotas. Only one person was selected as a respondent in each home. Investigators went to the house, asked about the inhabitants and then chose the first person they saw, who met the characteristics needed for the quotas. In-person interviews were conducted, which lasted for 30–45 min, depending on respondent availability and desire to talk.

Variables studied

The selection of variables for the current analysis was hypothesis driven based on previous literature on BP awareness, treatment and control in Africa.^{1, 2, 3}

Sociodemographic variables

The socioeconomic and demographic variables collected were:

• age (20–29/30–39/40–49/50 years and over)

• gender (male/female)

• educational level—defined in accordance with the educational system in Senegal—(0/1–5/6–9/10–12/over 12 years of school).

Biological health variables

The biological health variables collected were:

• BP: we used an OMRON M5-I digital automatic BP monitor (OMRON, s’Hertogenbosch, The Netherlands) to measure the participants’ BP. Measurements were made on the upper right arm using an appropriate-sized cuff while the participant was sitting after resting for 5 min. Three readings were taken during the interview. The first was discarded and the mean of the last two readings were used in the analysis. The first measurement was taken on both arms to detect a difference in BP between arms. Hypertension was defined as a systolic BP⩾140 mm Hg and/or a diastolic BP⩾90 mm Hg, or reported treatment for hypertension.²⁶ Awareness of hypertension was defined as any self-reported prior diagnosis of hypertension by a health-care professional among the population defined as having hypertension. Participants who were aware of hypertension were classified as being on treatment if they reported current use of drugs prescribed by a health professional, which they had taken within the past 2 weeks before the study. Control was defined as the proportion of the sample on antihypertensive therapy with BP <140/90 mm Hg.

• Body mass index (BMI) and waist circumference: anthropometric measurements were obtained with the participant in the standing position, wearing light clothing and no footwear. Weight was measured using a digital scale (Soehnle, Nassau, Germany; measurement accuracy of 100 g). To measure height, we used a Stature (height) Measuring Stand (GPM, Paris, France). Following World Health Organization recommendations, BMI was calculated by dividing weight (kg) by the square of the height (m²). Overweight was defined as 25⩽BMI<30, obesity corresponded to a BMI of ⩾30 and underweight to a BMI of <18.5.

Statistical analyses

Data was entered in Excel (2007), cleaned and exported to SPSS (version 16, IBM France, Créteil, France) for analysis. The proportion of the study subjects with hypertension, subjects who were aware of their condition and who were receiving treatment was determined by sex, age group, education level and BMI. Crude differences in these proportions across participant characteristics were determined using χ²-tests. A logistic regression was then conducted to identify independent factors associated with prevalence, awareness and treatment of hypertension. These were reported as odds ratios with corresponding 95% confidence intervals (CIs) of hypertension prevalence, awareness and treatment (as dependent variables) after adjustment for age, sex, education level and BMI (as independent variables). All analyses were performed using SPSS software, version 16. A P-value of<0.05 was considered statistically significant.

Results

Characteristics of the study sample

In our 2009 survey, most of the participants were aged <40 years. Twenty-three percent of the participants had no formal education and <20% had attended university (that is, >12 years).

Prevalence, awareness, treatment and control of hypertension

The prevalence of hypertension was 27.50% (95% CI: 23.93–31.07%). Prevalence of hypertension does not differ by gender (χ²=1.040, P=0.308; Table 1). However, prevalence of hypertension is significantly higher in those with no education (χ²=15.321, P=0.004) and among the older age brackets (χ²=121.445, P<0.001). Furthermore, hypertension is significantly related to BMI (χ²=49.950, P<0.001; Table 1). Among subjects with hypertension, the prevalence of awareness was 27.88% (95% CI: 21.04–34.72%).

Table 1 Prevalence of hypertension among women and men from dakar according to age, educational level and BMI (N=600)

The general rate of awareness is higher after 50 years of age (χ²=33.143, P<0.001) among women (χ²=7.959, P=0.005) and among overweight and obese subjects (χ²=6.146, P=0.013). No difference in hypertension awareness by educational level was noticed (χ²=2.875, P=0.238; Table 2).

Table 2 Sociodemographic characteristics and BMI by awareness and treatment among hypertensives (N=165)

Figure 1 shows that more than half of the hypertensive subjects who were aware of their condition were treated pharmacologically, corresponding with a prevalence of treatment among all of the hypertensives of 16.97% (95% CI: 11.24–22.70%). Among hypertensives, participants who were 50 years and older and who were overweight or obese were more likely to be receiving pharmacological treatment for their hypertension (χ²=18.625, P<0.001; χ²=6.371, P=0.012). However, no difference in hypertension treatment by sex and educational level was noticed (χ²=1.858, P=0.173; χ²=0.321, P=0.852; Table 2).

Figure 1

Prevalence of hypertension, awareness among hypertensives, treatment among those who were aware of hypertension and control among the treated hypertensives in Dakar.

Lastly, one-third of the treated hypertensives fulfilled criteria for control, corresponding to a prevalence of treatment among all of the hypertensives of 5.45% (95% CI: 1.67–8.32%). Unfortunately, the small number of individuals with controlled BP prevented us from testing the effect of sociodemographic variables and BMI on hypertension control.

The previously identified relationship between hypertension prevalence, awareness and treatment, and sociodemographic variables or BMI was tested by binary logistic regression. The results of the binary logistic regressions are presented in Tables 3 and 4.

Table 3 ORs for prevalence of arterial hypertension by sex, age, education level and BMI (N=600)

Table 4 ORs for awareness and treatment of arterial hypertension by sex, age, educational level and BMI (N=165)^a

In fact, results show that only age and BMI were associated with hypertension prevalence. People aged 50 years or more, as well as overweight or obese people, were more likely to have hypertension (Table 3). After adjustment for age, sex, educational level and BMI, the odds of hypertension awareness were higher among women and participants ⩾50 years old. Finally, in the multivariate analysis, only old age (⩾50 years) was independently associated with pharmacological treatment of hypertension (Table 4).

Discussion

Our study is the first to address the prevalence, awareness and control of hypertension on a representative sample of Dakar’s population. We observed an overall high prevalence of hypertension and low prevalence of awareness, treatment and control of hypertension. More than one-quarter of Dakar adults aged 20 years and more were hypertensive, but <30% of these subjects were aware of their condition. Even if more than half of the subjects who were aware of hypertension were on pharmacological treatment, only 32% of treated hypertensives fulfilled the criteria for control.

Despite the limitations of direct comparison owing to methodological heterogeneity, our estimates of hypertension prevalence in Dakar are in the upper range of contemporary data from Africa. These findings indicate that hypertension has become a major public health problem in Senegal, and underscore the urgent need to develop national strategies for prevention and treatment of hypertension in Dakar. As observed elsewhere, the prevalence of hypertension increases with increasing age^{1, 8, 27, 28, 29} and BMI.^{1, 2, 28, 30, 31} We found that the prevalence of hypertension was not associated with gender, as in most African populations.^{1, 17, 28, 32} Finally, educational level, which was associated with hypertension in χ²-tests, was no longer a risk factor for hypertension in logistic regression. This could be explained by the direct link between age and educational level, which is that older Dakar inhabitants being more illiterate than younger ones.

In Dakar, the prevalence of awareness is comparable to recent African surveys,^{3, 28} lower than in Ghana² and much below the average in developed countries.^{5, 27, 29, 30, 31, 33} Awareness was three times more frequent in women, as in other studies.^{3, 9, 27, 28, 29, 31, 33} The reasons for gender inequalities in the detection of hypertension are not well known, but many authors suggest that women’s more frequent contact with health services through maternity and child health programs allows greater detection of hypertension during pregnancy or the post-partum period.^{3, 17, 28} Moreover, older adults were more often aware of their hypertensive status than younger ones. A possible explanation might be that older people may pay more attention to their health.²

In our survey, <20% of the people with hypertension were treated. This very low level of treatment is comparable to other sub-Saharan countries.^{2, 3, 28} As in many developing countries, treatment of hypertension was nowhere near the ‘rule of halves’² and was well under the treatment rate in developed countries.^{29, 30, 31, 33} Moreover, the fact that hypertension treatment rises with age and is not associated with gender is consistent with other reports.^{2, 9, 27, 28}

Contrary to reports from the United States and Europe of higher prevalence of awareness and treatment in overweight and obese subjects,^{30, 31} our study showed no statistical association between BMI and hypertension awareness or treatment. A possible explanation might be that obesity or excess weight is not perceived as a risk factor for hypertension or any other health problem in Senegal. Stoutness is indeed socially valued in West Africa,³⁴ and consequently in Dakar it is possible that overweight or obese people feel no need to consult a health-care professional more often than other subjects, and thus do not present a higher prevalence in hypertension awareness or treatment. Finally, the prevalence of control was lower than the average in developed and in developing countries, including SSA.^{1, 2, 3, 9, 27, 28, 29, 30, 31, 33}

The study has some limitations. First, similar to that in many surveys our BP levels were based on the average of two measurements at a single visit, which may have overestimated the prevalence rates. Second, its cross-sectional design did not allow us to exclude reverse causation as the main explanation for some of the associations reported. Third, we were only able to consider pharmacological treatment. This is reductive because lifestyle changes are a fundamental part of BP control and should be considered as part of treatment. Fourth, we did not include in the study data on nutritional status and physical activity, which are major risk factors of hypertension. Other possible sources of bias include the documentation of self-reported hypertensive treatment by the participants. For example, subjects who incorrectly reported that they did not receive antihypertensive medication and had BP <140/90 mm Hg were considered normotensives. Finally, the limited sample size of our survey makes it difficult to generalize our findings to the Senegalese population, and the small absolute number of hypertensive subjects with controlled BP made it impossible to perform trend analysis on control of hypertension in age/sex subgroups.

In conclusion, our study shows that the epidemiological transition currently underway in Senegal is particularly associated with a high prevalence of arterial hypertension. Unfortunately, the health-care system in Senegal is largely restricted to communicable diseases and NCDs have not received the attention they deserve.³⁵ Yet, given the very low rates of awareness, treatment and control in our sample, it is clear that the mortality rate associated with arterial hypertension is more significant in Senegal than in developed countries, where treatment is more accessible and modern medicine more available. Thus, the observation made by the Global Burden of Disease study that ‘the probability of a man or woman dying from an NCD is higher in SSA and other developing regions than in established market economies’³⁶ still remains true 15 years later. Awareness of hypertension largely depends on the capacity of the health system to provide diagnostic services for hypertension to the general population.⁵ As public health measures and intensified antihypertensive treatment seem to be effective in improving BP control rates, developing strategies for averting an NCD epidemic must be a priority objective.