Modifiable stroke risk factors in Africa: lessons from SIREN
Authors: Andre P Kengne, Bongani M Mayosi
Journal: The Lancet Global Health (2018)

According WHO estimates, cardiovascular diseases are the second most common cause of death in Africa.1WHOGlobal health estimates 2015: deaths by cause, age, sex, by country and by region, 2000-2015. World Health Organization, Geneva2016Google Scholar Of the prevailing cardiovascular diseases in Africa, stroke was the top killer and the fourth leading cause of all deaths in 2015.1WHOGlobal health estimates 2015: deaths by cause, age, sex, by country and by region, 2000-2015. World Health Organization, Geneva2016Google Scholar Globally, the highest age-standardised incidence of stroke is in Africa.2Walker R Whiting D Unwin N et al.Stroke incidence in rural and urban Tanzania: a prospective, community-based study.Lancet Neurol. 2010; 9: 786-792Summary Full Text Full Text PDF PubMed Scopus (178) Google Scholar Hitherto, however, the epidemiology of stroke in Africa has not been characterised optimally,3Kengne AP Anderson CS The neglected burden of stroke in sub-Saharan Africa.Int J Stroke. 2006; 1: 180-190Crossref PubMed Scopus (72) Google Scholar leading to ineffective prevention and control. In The Lancet Global Health, Mayowa Owolabi and colleagues4Owolabi MO Sarfo F Akinyemi R et al.Dominant modifiable risk factors for stroke in Ghana and Nigeria (SIREN): a case-control study.Lancet Glob Health. 2018; (published online Feb 26.)http://dx.doi.org/10.1016/S2214-109X(18)30002-0Summary Full Text Full Text PDF PubMed Scopus (139) Google Scholar report results from a case-control study done across 15 health facilities in Ghana and Nigeria to identify and quantify the contribution of leading risk factors for stroke. The study involved 2118 adults with acute stroke (68% of which were ischaemic) and 2118 stroke-free controls, matched for sex, age, and ethnicity, recruited into the SIREN study. Using conditional logistic regression and population-attributable risk (PAR), more than 30 potentially modifiable risk factors were screened, of which 11 emerged as the most important contributors to stroke occurrence. Expectedly, hypertension had the highest contribution, with other factors in decreasing order including dyslipidaemia, regular meat consumption, elevated waist-to-hip ratio, diabetes, low green leafy vegetable consumption, stress, added salt at the table, cardiac disease, physical inactivity, and tobacco use. Ten of these factors were associated with ischaemic and six with haemorrhagic stroke. Altogether, these 11 factors accounted for 98·2% (95% CI 97·2–99·0) of the PAR associated with total stroke, consistently across some subgroups, but not all. Owolabi and colleagues conclude that implementing population-level interventions targeting these factors will substantially reduce stroke burden among African populations. SIREN was modelled on the global INTERSTROKE case-control study,5O'Donnell MJ Chin SL Rangarajan S et al.Global and regional effects of potentially modifiable risk factors associated with acute stroke in 32 countries (INTERSTROKE): a case-control study.Lancet. 2016; 388: 761-775Summary Full Text Full Text PDF PubMed Scopus (1005) Google Scholar and largely used internationally validated tools for stroke risk assessment. With over twice the number of African participants in INTERSTROKE, SIREN had superior power to provide context-specific information relating to stroke subtypes, risk factors, and potential effects that had been previously reported in other regions. However, residual issues remain regarding the inclusion of both community and hospital-based controls; the suboptimum assessment of risk factors, their differential assessment in cases and controls, or both; and the non-inclusion of early mortality data and assessment of the effects of identified risk factors on this outcome. PAR is derived as the difference between the incidence of a disease in the total population and the incidence in the subpopulation unexposed to the targeted risk factor. Measures of incidence are estimated from case-control studies only under special circumstances not met by the SIREN study. However, the PAR% is calculable for most case-control studies and is the measure estimated by the SIREN investigators. PAR% is the proportion of disease that is attributable to an exposure of interest. In the case of SIREN, one could state that 98·2% of acute stroke in the SIREN population was attributable to 11 risk factors. Theoretically, the PAR% is the proportion of stroke events that would be averted if the 11 factors were eliminated. In practice, however, first, the counterfactual scenario of no exposure might not be attainable; second, the exposure needs to be causal for the elimination to reduce stroke occurrence; and, third, even if the exposure was causal, ascertaining whether those factors really contributed to stroke in all exposed people is difficult. In some exposed people, other causal factors, including unmeasured factors, could account entirely for the occurrence of the stroke. The chief application of PAR% is in helping policymakers to plan public health interventions as a measure of the effect on public health. PAR% is a function of the magnitude of the association (odds ratio in SIREN) between the risk factor and outcome of interest, as well as the prevalence of that risk factor in the population (control group of SIREN). Even under the assumption of a constant magnitude of the association, the prevalence of risk factors varies across and within populations. These variations would largely explain differences in PAR% observed across subpopulations in SIREN, and between SIREN and other studies. Population estimates of risk factors are subject to several biases, particularly in case-control studies; thus, caution is needed in interpreting differences in PAR% within SIREN and across studies. From a public health perspective, interventions exist to prevent and control stroke and other non-communicable diseases (NCDs) in Africa. Cost-effective interventions, recently summarised elsewhere,6Prabhakaran D Anand S Watkins D et al.Cardiovascular, respiratory, and related disorders: key messages from Disease Control Priorities.Lancet. 2017; (3rd edition) (published online Nov 3.)http://dx.doi.org/10.1016/S0140-6736(17)32471-6Summary Full Text Full Text PDF Scopus (71) Google Scholar include, on a population level, tobacco taxation, bans of trans fats, and compulsory reduction of salt in manufactured foods products; and primary health service strengthening by establishing locally endorsed guidelines and ensuring availability of essential medications for risk factors management.6Prabhakaran D Anand S Watkins D et al.Cardiovascular, respiratory, and related disorders: key messages from Disease Control Priorities.Lancet. 2017; (3rd edition) (published online Nov 3.)http://dx.doi.org/10.1016/S0140-6736(17)32471-6Summary Full Text Full Text PDF Scopus (71) Google Scholar Most of these recommendations are included in strategy documents for NCD prevention and control in Ghana and Nigeria.7Non-Communicable Disease DivisionFederal Ministry of Health. National strategic plan of action on prevention and control of non-communicable disease. Abuja, Nigeria.https://drive.google.com/file/d/0B1DAmtM1BcbMMG5pVEJwYXgzS2c/viewDate: 2015Google Scholar, 8Republic of Ghana Ministry of HealthStrategy for the management, prevention and control of chronic non-communicable diseases in Ghana 2012–2016.https://extranet.who.int/nutrition/gina/sites/default/files/GHA-2012-NCDs.pdfDate: 2012Google Scholar At the continent level, the Pan-African Society of Cardiology (PASCAR) has identified hypertension as the priority condition for action to reduce cardiovascular disease in Africa.9Dzudie A Rayner B Ojji D et al.Roadmap to achieve 25% hypertension control in Africa by 2025.Glob Heart. 2017; (published online Oct 14.)DOI:10.1016/j.gheart.2017.06.001Crossref PubMed Scopus (48) Google Scholar PASCAR has issued a ten-point action plan to increase treatment and control rates for hypertension by 25% in Africa by 2025. In general, however, African countries are doing less than required to meet their NCD prevention and control objectives.10Nyaaba GN Stronks K de-Graft Aikins A Kengne AP Agyemang C Tracing Africa's progress towards implementing the Non-Communicable Diseases Global action plan 2013–2020: a synthesis of WHO country profile reports.BMC Public Health. 2017; 17: 297Crossref PubMed Scopus (55) Google Scholar The SIREN study is an adequate response to the dire need for locally relevant research to contextualise prevention and control solutions for NCDs in Africa. However, the scope of data needed is broad. More implementation research is needed to support successful prevention of stroke and other NCDs across the continuum of risk exposure, while high-quality community-based stroke incidence studies are needed to map out the burden and monitor interventions.3Kengne AP Anderson CS The neglected burden of stroke in sub-Saharan Africa.Int J Stroke. 2006; 1: 180-190Crossref PubMed Scopus (72) Google Scholar We declare no competing interests. Dominant modifiable risk factors for stroke in Ghana and Nigeria (SIREN): a case-control studyImplementation of interventions targeting these leading risk factors at the population level should substantially curtail the burden of stroke among Africans. Full-Text PDF Open Access