EPIDEMIOLOGY OF HYPERTENSION IN YEMEN (HYpertension and Diabetes in Yemen - HYDY Study): EFFECTS OF GEOGRAPHICAL AREAS

Introduction Although globalization in the developing countries can contribute to increase the prevalence of high blood pressure (BP) by spreading unhealthy lifestyle and dietary habits, it might offer favorable opportunities by improving the dissemination of knowledge and by achieving a high level of education, as well as by increasing contacts with health services. In Yemen the transportation system is poor. Thus, extending the few information available regarding the prevalence, awareness, treatment and control rates of hypertension, which are limited to the capital area to a national level, might lead to biased results. The HYDY (HYpertension and Diabetes in Yemen) study was therefore performed by stratifying the country into three different geographic areas (capital, inland, coast) to investigate the effects of urbanization, geographical area, and air temperature on hypertension burden and kidney damage. Design and methods: A multistage stratified sampling method was used: - in the first stage, Yemen was stratified into 3 regions, capital area, inland and coast selected to be representative of the country: - in the second stage, rural and urban regions were identified from each area; - In the third stage, districts were identified within each urban and rural region; - in the final stage, 250 adult participants from each district were allocated to a cluster stratified by gender and age decades years (25-34; 35-44; 45-54; 55-69) to a total of 10 000 individuals. All subjects (n=10242) received two visits separated by few days to confirm the diagnosis of hypertension. Hypertension was defined as systolic BP >= 140 mmHg and/or diastolic BP >= 90 mmHg and/or self-reported use of antihypertensive drugs. Prevalence rates were weighted to represent the Yemeni population aged 15-69 years in 2008. Air temperature was measured at participants home using digital thermometers (Checktemp, Hanna Instruments, Italy) (accuracy: ± 0.3 1C; range 20 to 90 1C). Covariates included gender, age in decades, living area (rural/urban), geographical area, air temperature and education level. The model was also adjusted for potential confounders including co-morbidities (diabetes mellitus, overweight or obesity, high cholesterol and high triglycerides, and behavioral factors (sedentary lifestyle, smoking, fruit and vegetable consumption). Results Overall 1307 participants fulfilled the criteria of hypertension, corresponding to an age (15-69 years) weighted prevalence of 7.7% (95% CI 7.2 to 8.1). When compared to urban dwellers, rural dwellers had similar hypertension prevalence (adjusted OR 1.03;95% Cl 0.91 to 1.17). However, at logistic regression analysis (adjusted for age, urban/rural residency, demographic characteristics, air temperature, health behavior, risk factors, and associated clinical conditions) rates of hypertension progressively increased from the capital (6.4%; 5.8 to 7.0), to inland (7.9%;7.0 to 8.7), to the coastal area (10.1%;8.9 to 11.4). At logistic regression analysis differences between geographic areas were independent of urban/rural residency, demographic characteristics, air temperature, health behavior, risk factors and associated clinical conditions (Figure 1). Regional variations in rates of hypertension were associated with changing rates of awareness, treatment and control. Self-reported BP measurement, hypertension awareness, drug treatment and BP control were favorably affected by living in the capital area. The average air temperatures recorded at participants' homes were 22.0 °C (95% CI 21.9-22.1 °C) in the capital area, 25.4 1C (25.3-25.5°C) in the inland and 28.3 °C (28.1-28.4 °C) in the coastal area. Air temperature (although significant) limited only the effect on hypertension prevalence estimation (B coefficient 0.020 ± 0.010). A negative correlation between temperature and BP was reported and geographic distribution of hypertension burden follows an opposite direction than average air temperature measured during home visits, as hypertension prevalence is higher in the coast than in the highlands Discussion In Yemen, the prevalence of hypertension is low, probably because the country is still in the first stages of the epidemiological transition. According to this large population study, hypertension prevalence is not affected by urban or rural residency and is favorably affected by urbanization and by living in the capital area. One of the most important HYDY findings is the regional variation in hypertension prevalence as hypertension rates are higher in the in remote areas of the country.