Prehypertension and Hypertension among Schoolchildren in Brazzaville, Congo

Background. To determine the prevalence and associated factors of prehypertension (pre-HT) and hypertension (HT) in schoolchildren at Brazzaville (Congo). Methods. This cross-sectional study was conducted from March to May 2011 in five representative urban schools in Brazzaville. American Pediatric Society's definition of pre-HT and HT was used. The measurement of blood pressure was obtained using auscultator method. Univariable and multivariable analyses were performed to establish associations between blood pressure levels and sociobiographical factors. Results. 603 children were included. The mean age was 11.8 ± 3.6 years (range 5–18 years). The prevalence of pre-HT was 20.7% (n = 125). Factors associated with pre-HT were secondary school (P = 0.02), private schools (P < 0.004), migrants (P = 0.03), the obese (P = 0.004), high socioeconomic level (P < 0.01), and overweight (P = 0.02). In logistic regression, the independent determinants of pre-HT were secondary school (P = 0.0001), migration (P = 0.04), obesity (P = 0.004), and overweight (P = 0.01). The prevalence of HT was 10.1% (n = 61) during the first screening and 3.3% (n = 20) in second screening. The independent determinants of HT were obesity (P = 0.0001) and overweight (P = 0.0001). Conclusion. Pre-HT and HT are emerging as a mass problem in Congolese schoolchildren with urban migration and overweight/obesity to be controlled and prevented.


Introduction
Hypertension (HT) in children is a rare concern whereas HT in adults is a global public health problem, according to World Health Organization (WHO) [1]. The prevalence of HT is reported in 4 to 15% children worldwide [2], with increasing trends during recent decades [3,4]. This increase is attributable to particular stress of mega cities in industrialized countries and lifestyle and diet whose impact on body size is well established. In sub-Saharan Africa (SSA) which is facing epidemiological transition, the prevalence of HT in child varies by regions: 4.9% in schools from Sudan [5] and 29.4% from South Africa [6]. However, no data on HT and prehypertension (pre-HT) is available in schoolchildren from Republic of Congo.
The objectives of this study were to determine the prevalence of pre-HT and HT and to identify its contributing factors, which would establish an effective prevention program starting from a young age in Brazzaville, Congo.   [7]. Thus, the calculated sample size was 600 + 6 (10% potential missing) = 606 eligible schoolchildren. The parents, schoolchildren, and schools responsible authorities were sensitized about the aim, the significance, and the timetable for the study. Ethical issues were taken into account according to the Helsinki Declaration. The learners were interviewed and examined by investigators after prior training. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were recorded three times according to the American Pediatrics Society recommendations, using auscultatory method [8] by aneroïde sphygmomanometer (Spengler, France). The average of three taken pressures was retained.

2.2.
Variables. The analyzed variables were age (years), sex, weight (kg), height (cm), and body mass index (BMI) in kg/m 2 , malnutrition, overweight, obesity, adolescence, migration, number of siblings, promiscuity, school sector activity (primary, secondary, public, and private), high socioeconomic level, SBP in mm Hg, DBP in mm Hg, pulse pressure (PP) in mm Hg, HT, and pre-HT.

Definitions.
Adolescence was defined by WHO. Migration is defined by expatriation in Brazzaville since three years. Promiscuity was considered the presence of at least three children in the bedroom. The high socioeconomic level was defined according to parental occupation, namely, civil servants, traders, or a higher income than twice the minimum salary in Congo. Malnutrition was defined for BMI < 5th percentile of WHO reference, overweight for BMI between 85th and 95th percentile, and obesity for BMI > 95th percentile [9]. Pre-HT was defined for SBP and DBP between 85th and 95th percentile of American Pediatrics Association curves reference [10]. HT was defined by SBP and DBP ≥

Statistical
Analysis. Data were expressed as proportions for categorical variables and as mean ± standard deviation for continuous variables. In univariate analysis, Student ttest, chi-square test, and odds ratio (OR) with 95% confidence interval (CI) were used for comparisons of means and proportions and associations, respectively. In multivariate analysis, after adjusting for confounding factors, logistic regression models identified independent determinants of pre-HT and HT. The criterion for statistical significance was value < 0.05. All analyses were performed using SPSS software version 10.0 for Windows (SPSS Inc., Chicago, IL, USA).
The prevalence of HT in the first screening was 10.1% ( = 61 cases) and 3.3% ( = 20) in the second screening. There were 12 girls and 8 boys and the mean age of HT children was 12.8 ± 2.6 years versus 11.8 ± 3.7 years for children without HT ( > 0.05). The BMI of children who had HT was 20.3 ± 4.4 kg/m 2 versus 17.7 ± 3 kg/m2 for children without HT ( < 0.001). Only overweight and obesity had a positive and significant univariate association with HT (Table 5). In logistic regression, the independent determinants of HT (Table 6) were obesity ( = 0.0001) and overweight ( = 0.0001).

Discussion
This study reported the burden and contributing factors of pre-HT and HT in a sample of schoolchildren in Brazzaville, Congo. Rigorous sampling criteria of this study and that of other authors [10] demonstrated high rates of high blood pressure.
The prevalence of pre-HT was 20.7% associated with several factors in the present survey. These contributing factors included private school, secondary school, migrant children, children belonging to a family of high socioeconomic status, children with obesity and overweight, and adolescents. Prevalence of pre-HT varies by puberty, country, and social environment (degree of urbanization  [14]. However, higher rates of pre-HT were reported by this study and estimated 20.7% and similar with 22.2% and 25% among Nigerian adolescents from rural and urban areas, respectively [15]. Agyemang et al. in Ghana found that the level of blood pressure increased with age, and this was more pronounced in urban areas [16]. These facts were also reported by Paradis  et al. in USA, with a prevalence of 12% for children aged 9 years, 22% for children aged 13 years, and 30% for children aged 16 years ago [17]. As remote areas, however, aging was not associated with increasing blood pressure among these Congolese schoolchildren.
The most important determinants of pre-HT in this survey were migration, obesity, and overweight. The literature reports much higher prevalence of pre-HT children with overweight or obesity [6,18,19]. Moreover, after migration from rural areas toward town of Brazzaville, urbanization and westernization are driving both epidemiological transition and nutrition transition characterized by changes in lifestyle and dietary habits. Thus, physical inactivity, excessive intake of salt, refined sugar, and polysaturated fats increase the risk of overweight/obesity and cardiovascular risk among children [20,21]. But these factors are difficult to evaluate in our context. Other risk factors were found. These include children in secondary schools, private schools, and children with high socioeconomic level. Indeed, the majority of high school students are adolescents, in which a high prevalence of pre-HT is described by other authors [4,15,17,22,23]. In this study, the HT was found in 10% of children in Brazzaville, Congo. It is reported that repeated blood pressure measurements and screening may reduce prevalence of HT in some data from the literature [24], but not in the present study. The prevalence of HT varies by the country of residence and age [24]. The prevalence of HT is continuously increasing in developing countries as shown by Chiolero et al. in the Seychelles: 6.9% of children in 2004 and 7.8% in 2006 [3]. In Africa, low prevalences of HT were reported as 4.9% in Sudan [5] and 4% in Egypt [11]. On the other hand, the rate of 10.1% hypertensive black Bantu Congolese children in this study is intermediate between those from non-Bantu Sudanese and Egyptian children [5,11] and that of 29.4% black Bantu South African children [6]. These differences are related to standards of developing or emerging economies, overweight/obesity [17][18][19], and ethnic/genetic factors [3,22].
Disparities were also found outside of Africa, such as 1.08% in Argentina [25], 7.4% in Canada [12], and 19.6% in Greece [26], highlighting not only the level of development, but also the impact of policies to prevent these countries [4]. Variations in prevalence have been reported within the same country. This is the case of China, where the prevalence of 9.8% to 20.2% was observed from different regions [14,27]. These gaps are certainly explained by differences of development between regions of high growth in this country. On the other hand, in India, the prevalence appears to be more constant, which Genovesi et al. reported as 5.2% [28], Sharma et al. as 5.9% [13], and Buch et al. as 6.48% [29]. Indeed, in this country, although the economic emergence is initiated, the divisions are still significant and the social level is still low, with non-westernized eating habits [13].
Unlike pre-HT only overweight and obesity were risk factors of HT in our study. Indeed, it is both classic factors of HT in children in various parts of the world [17][18][19].

Conclusion
Both prevalences of pre-HT and HT are recognized as a public health problem in schoolchildren from Brazzaville, Congo. The most important contributing factors for pre-HT and HT are migration, overweight, and obesity. Prevention and control of the consequences of lack of education are needed urgently in Congolese children.