Fast track ā ArticlesGlobal variation in stroke burden and mortality: estimates from monitoring, surveillance, and modelling
Introduction
WHO has estimated that in 2002 there were 15Ā·3 million strokes worldwide, more than a third of which (5Ā·5 million) resulted in death.1 Given that there were 57 million deaths worldwide in 2002, stroke accounted for nearly 10% of all deaths. Although most research and attention to prevention and intervention occurs in high-income countries, more than 85% of strokes occur in low-income and middle-income countries.2, 3 Furthermore, despite shorter life expectancies than in high-income countries, 87% of the burden of stroke, as measured in disability-adjusted life years (DALYs), is borne by low-income and middle-income countries, where stroke ranks fifth overall, just below HIV/AIDS, as the cause of lost DALYs. 85% of the world's population lives in low-income and middle-income countries, and whether the burden of stroke is disproportionately greater in these countries has not been systematically assessed.
The results of several studies have suggested that income is a predictor of stroke risk. Age-adjusted rates of ischaemic stroke are high in the poorest people.4 Stroke mortality in the USA is strongly related to the income of the county of residence.5 At a national level, a study that assessed stroke mortality rates for 1968ā94 in 51 countries showed that mortality rates were generally lower in high-income countries than in low-income countries and that stroke mortality rates increased in several countries as economic conditions worsened, particularly those countries in the former Soviet Union.6 A systematic review of population-based studies from 1970ā2008 showed a 42% decrease in stroke incidence in high-income countries and a greater than 100% increase in stroke incidence in low to middle income countries. Furthermore, in 2000ā08 the overall stroke incidence rates in low to middle income countries exceeded for the first time the rates of stroke incidence in high-income countries.7 Recently, the methods for obtaining national estimates of stroke mortality and burden have improved, and data on mortality are now available for more than half the member countries of WHO.8
Few resources are allocated to stroke prevention and treatment in low-income countries, and infectious diseases are often prioritised.9 Whether the disproportionate burden of modifiable risk factors for stroke (eg, hypertension, diabetes, tobacco use, alcohol abuse, and obesity) that are borne by low-income countries could account for a disparity in risk is unclear.10, 11, 12 To begin to gauge the overall need and potential targets for intervention, we assessed national differences in stroke mortality and DALY rates worldwide and assessed whether differences in economic conditions were associated with disparities in stroke mortality and burden. We also assessed whether the prevalence of risk factors for cardiovascular disease, as measured in current surveillance programmes, could account for the effect of differences in national income on burden and mortality. For these analyses, we combined data derived from systematic reviews and from models as part of the WHO Global Burden of Disease and InfoBase projects and from surveillance data from specific WHO programme offices.
Section snippets
Methods
Global measures of disease burden were derived from the WHO Global Burden of Disease project.1 This comprehensive programme combined records of national vitality with the results from epidemiological studies, which are reviewed by staff and experts, and uses validated models to produce comparable estimates of national burden. The project is complex and has had many revisions, which are listed in a series of publications and working papers that can be accessed through the WHO website.1
Results
Age-adjusted and sex-adjusted mortality rates for cerebrovascular disease varied ten-fold between countries, from 24Ā·5 per 100ā000 in the Seychelles to 251 per 100ā000 in Russia (table 1). Eastern Europe, north Asia, central Africa, and the south Pacific were over-represented among countries with the highest stroke mortality rates, whereas western Europe and North America were over-represented among those with the lowest stroke mortality rates (figure 1). For age-adjusted and sex-adjusted rates
Discussion
Stroke mortality rates vary across the globe, with a ten-fold difference in age-adjusted mortality rates and DALYs lost between the highest and lowest ranked countries. Regional differences are apparent, with a higher burden in north Asia, eastern Europe, central Africa, and the south Pacific. National income was a particularly strong predictor of stroke burden and mortality. Mortality rates were 3Ā·5-fold higher in low-income countries than in middle-income and high-income countries; DALY loss
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