Fast track — ArticlesRisk factors for ischaemic and intracerebral haemorrhagic stroke in 22 countries (the INTERSTROKE study): a case-control study
Introduction
Stroke is the second leading cause of death worldwide, and the leading cause of acquired disability in adults in most regions.1, 2 Countries of low and middle income have the largest burden of stroke, accounting for more than 85% of stroke mortality worldwide, but few reliable data are available to identify risk factors for stroke in most of these regions, and particularly for haemorrhagic stroke.1, 2, 3, 4, 5
Findings from the INTERHEART study6, 7, 8, 9, 10 suggested that nine modifiable risk factors explain most of the risk of myocardial infarction worldwide. An equivalent study is needed for stroke because stroke has several pathologies other than large artery atherosclerosis,11 so risk factors for stroke and its aetiological subtypes could differ from those for myocardial infarction. Furthermore, the independent contribution of each risk factor to the burden of stroke worldwide—the population-attributable risk (PAR)—is unknown in most regions.
The INTERHEART study showed the feasibility, value, and importance of a large standardised international case-control study (29 972 participants) to establish the importance of, and relation between, key risk factors for myocardial infarction in 52 countries of high, middle, and low income, with participation from every inhabited continent.6, 7, 8, 9, 10 However, additional challenges are presented by a similar study for stroke. In particular, routine neuroimaging is needed to establish primary stroke subtypes (ischaemic vs haemorrhagic), and patients with disabling stroke who are unable to communicate need to be represented in the study.
The INTERSTROKE study is an international, multicentre, case-control study, designed to establish the association of traditional and emerging risk factors with stroke (and primary stroke subtypes) in countries of high, middle, and low income. We report the results of phase 1 of 3000 cases and 3000 controls from 22 countries, showing that an international case-control study is feasible for stroke, and provide estimates of the importance of common risk factors. Phase 2 is underway and is expected to be completed in the next 3 years.
Section snippets
Participants
The design of the INTERSTROKE study has been reported previously,12 and we provide a brief summary. Participants were recruited from 84 centres in 22 countries: Argentina, Australia, Brazil, Canada, Chile, China, Colombia, Croatia, Denmark, Ecuador, Germany, India, Iran, Malaysia, Mozambique, Nigeria, Peru, Philippines, Poland, South Africa, Sudan, and Uganda. Phase 1 lasted from March 1, 2007, to April 23, 2010.
Cases were admitted to hospital with first acute stroke, defined as “a clinical
Results
A screening log was maintained for about 3 months in 42 centres from 14 countries. Of 5668 patients in the screening log, 762 (13%) were eligible to be included in phase 1. The most common reasons for ineligibility were: patient had had a previous stroke (n=1199, 24%); stroke did not meet the clinical definition (n=871, 18%); time window for symptom duration was exceeded (n=1294, 26%); and patient was unable to communicate because of severe stroke, aphasia, or dementia, and did not have a valid
Discussion
The INTERSTROKE study is the first large standardised case-control study of risk factors for stroke in which countries of low and middle income were included, and all cases completed routine neuroimaging. Our findings showed that five risk factors accounted for more than 80% of the global risk of all stroke (ischaemic and intracerebral haemorrhagic): hypertension, current smoking, abdominal obesity, diet, and physical activity. With the addition of five other risk factors, including
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