The scale of the surveys described in this study is unique, demonstrating the magnitude of the problem of hypertension in different countries in SSA, including rural and urban areas. The four populations are very different in terms of socioeconomic status, living environment and geographical location. Yet, hypertension was the most frequently observed risk factor for CVD and determinants for blood pressure were similar, in all four populations. The prevalence of hypertension observed in our survey in the Greater Windhoek area in Namibia was remarkably high (crude 32%, age-standardized 38%). This prevalence is similar to the prevalence of hypertension in adults in the USA where an overall prevalence of 31% in adults and 38.6% in non-Hispanic blacks was reported 
. The prevalence of hypertension in rural Nigeria is lower compared to in high income countries or in other parts of SSA 
, as can be expected in a rural community where people are more likely to follow a traditional African lifestyle. However, both mean blood pressures and the prevalence of hypertension in the Nigerian study population were much higher compared to early studies in rural populations in SSA 
. The rapid changes towards a more Western lifestyle that are taking place in LMIC is likely to contribute to an increase in the prevalence of hypertension in the coming years, in both rural and urban areas 
. Whereas mean systolic blood pressure is decreasing since 1980 in high income countries, trends in blood pressure show an increase in systolic blood pressure in many SSA regions and mean systolic blood pressures in SSA are amongst the highest in the world 
. In addition, people of black African origin have been identified as having a higher risk of target organ damage compared to Caucasians for a given blood pressure 
and the onset of CVD in LMIC countries occurs at an earlier age compared to high income countries 
. Finally, even though the prevalence of hypertension in SSA is still lower compared to the high income regions, the large and growing population of LMIC such as Nigeria will result in a considerably larger absolute number of individuals affected compared to high income countries 
. A recent study in rural Kenya found a similar prevalence of hypertension 
as our study whilst surveys in urban Tanzania found a higher prevalence 
. The Tanzanian and Kenyan study populations in our surveys consisted of individuals and their household members, participating in a microcredit program and in a dairy cooperative respectively. These specific characteristics preclude generalization of our conclusions regarding the prevalence of hypertension to the general urban population of Tanzania or the rural population of Kenya. Previous research showed large regional differences in hypertension prevalence in SSA, depending on the level of urbanization and other environmental and possibly genetic factors, although the available data is limited 
. Therefore, our surveys are not representative for the whole continent of Africa but should be regarded as a contribution to filling the gaps in knowledge on regional prevalence data.
The prevalence of hypertension was based on three measurements of blood pressure on one occasion in this study. In clinical practice, a diagnosis of hypertension requires multiple measurements on several occasions. Therefore, the prevalence of hypertension found in our surveys might be an overestimation, although the normal mean heart rate did not support high blood pressure readings due to sympathic activation. Our study does not allow differentiating between primary and secondary hypertension. To the best of our knowledge, there are no data available on the prevalence of secondary hypertension and the underlying causes in the population from SSA.
Early identification and treatment of people with hypertension is vital. The proportion of respondents with hypertension on treatment was low in Nigeria, Kenya and Tanzania. The proportion on treatment increased with more severe hypertension. Blood pressure control as low as 2.6% (Kenya) is of concern and in line with previous findings from SSA 
. Poor access to health care, in particular availability and affordability of drugs and travel costs, are barriers to CVD prevention treatment in LMIC. There is an ongoing debate about whether limited funds in LMIC should be spent on NCDs if the burden of communicable diseases is still high 
. Lifestyle interventions such as salt reduction or weight loss are cheap interventions that might be cost saving 
. These lifestyle interventions are reported to reduce blood pressure with 3–4 mmHg systolic and 2–3 mmHg diastolic 
. In our study, between 29.2% (Namibia) and 43.3% (Nigeria) of the respondents with hypertension had grade 2 or grade 3 hypertension. Therefore, our data show that a large proportion of the patients with hypertension may not be adequately treated with lifestyle interventions only. In these groups, drug treatment will be necessary to achieve target goals. Individual (drug) interventions for CVD prevention for high risk groups are available and were shown costs effective in modeling studies 
. Calculation of total absolute CVD risk according to WHO risk charts did not contribute to identification of respondents eligible for antihypertensive drug treatment other than those with high blood pressure. WHO classifies individuals with blood pressure at or above 140 mmHg systolic or 90 mmHg diastolic eligible for treatment if 10 year CVD risk is ≥20%. Individuals with blood pressure 160 mmHg systolic or 100 mmHg diastolic are eligible for treatment regardless of other risk factors 
. Due to the low prevalence of diabetes and smoking, treatment eligibility was entirely driven by blood pressure. However, respondents with higher blood pressure were more likely to have other CVD risk factors such as high cholesterol, larger waist circumference and diabetes (Table S1A
–D). This clustering of risk factors is important as it increases a persons' overall CVD risk.
Our surveys have all been conducted as part of an evaluation to assess the impact of private health insurance schemes for low and middle income groups in SSA. There is increasing advocacy for affordable health insurance schemes as part of a broader solution to health care financing problems in LMIC 
. Health insurance may be helpful to improve access to care, especially for patients with chronic conditions such as hypertension. Strengthening of current health systems and improving access to care for patients in LMIC is essential and was recently recommended in the UN declaration resulting from the UN High-Level Meeting on Non-Communicable Diseases 
. Our data from Namibia showed that treatment and control rates for hypertension were higher for those insured, although no conclusion about improved access to care can be drawn based on these data as people with hypertension might be more likely to enroll in insurance schemes.
We conclude that hypertension is the most frequently observed CVD risk factor in both urban and rural communities in multiple regions in SSA. The prevalence is expected to increase in the coming years. The determinants of blood pressure were consistent in all study populations and similar to described in other populations. Low levels of awareness, treatment and control of hypertension are alarming and may reflect poor access to care. Strengthening of health care systems in SSA to contain the emerging epidemic of CVD is urgently needed.