(Stroke. 1995;26:541-542.)
© 1995 American Heart Association, Inc.
Articles |
Monitoring Stroke
An International Challenge
From the University Geriatric Unit, Department of Medicine (R. Bonita), and the Department of Community Health (R. Beaglehole), School of Medicine, University of Auckland (New Zealand).
Correspondence to Ruth Bonita, MPH, PhD, University Geriatric Unit, North Shore Hospital, PB 93-503, Takapuna, Auckland 9, New Zealand.
Key Words: epidemiology • incidence • mortality • registries • stroke • World Health Organization
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Introduction |
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Worldwide, there are approximately 4.6 million deaths from stroke each year, and three quarters of these occur in developing countries.1 This estimate is based on death certificate data, which cover only about one third of the world's population, and extrapolation from total mortality rates. Despite their limitations, death certificate data show that in recent decades stroke death rates have declined dramatically, at least in industrial countries, with as much as a 7% per annum decline occurring in Japan since the mid-1970s.2 Where death certificate information is available in developing countries, the general trend is also downward. Not all countries have benefited, however; countries in the eastern European region are still registering high stroke death rates. Within countries, ethnic, geographic, and social class differences remain, with the persistent "Stroke Belt" in the southern United States providing an excellent example of within-country geographic variation.3
Such variations should help our understanding of the epidemiology of stroke. If first strokes are being prevented, then the decline in death rates represents a major public health achievement. If, on the other hand, the decline is a result of improvements in survival of stroke patients, there are major implications for health planners because of the global aging of populations.
To a large extent, explanations for the differing mortality trends have been a matter of speculation and supposition. What is needed is information on changes over time in incidence and case-fatality rates. Two types of studies have been used to explain long-term trends: cohort studies and stroke registers. A number of important community-based cohort studies have measured stroke incidence, notably in the United States and Japan, but these have been limited by the small annual number of strokes.4 5 6 The increasing availability of computed tomographic scans may have influenced diagnostic decisions that previously were based on clinical criteria alone. Tentative conclusions from these studies suggest that improvements in case-fatality rates, rather than a decline in incidence, are the more likely explanations for the mortality decline.
An increasing number of population-based stroke registers have been developed in the past decade. These registers have contributed to an understanding of the size of the problem for the communities and, for some, to a measure of change in event rates over time.7 8 9 Criteria for well-designed stroke registers include prospective registration of acute stroke events in large representative populations and comprehensive case-finding methods to identify fatal and nonfatal events occurring both in and out of the hospital.10 Even with adherence to these guidelines, it has been difficult to accurately measure stroke in such a way as to allow meaningful comparisons within and between countries. The difficulties of identifying all acute cases occurring in a population cannot be underestimated.
Two articles published in the March issue of Stroke represent an important step in addressing geographic differences in stroke incidence.11 12 These articles represent the first collaborative results of the stroke component of the World Health Organization (WHO) Monitoring Trends and Determinants in Cardiovascular Disease (MONICA) Project, the largest epidemiological study of heart disease and stroke undertaken thus far. This project is a 10-year study monitoring cardiovascular disease in 35 defined populations in 21 countries on four continents.13 The main focus of the MONICA Project has been on coronary heart disease, acute myocardial infarction, and coronary care. The stroke component of MONICA has taken a secondary position. The stroke study encompasses 21 centers in 11 countries and covers a total population of 2.9 million men and women aged 35 to 64 years. While most of these centers are based in northern and central Europe, Russia and China are also represented. Despite the fact that stroke is a condition that affects elderly people, only seven of the populations have extended their registers to include people up to the age of 75 years. From a health service point of view, monitoring stroke in the older age groups should also receive priority.
The detailed evaluation of the coverage and quality of the stroke registers by Asplund and colleagues11 confirms earlier reports of the difficulties of monitoring stroke. The value of this report lies in describing the steps necessary to implement standard definitions and criteria and to achieve complete case ascertainment. The publication of the article on quality control with the article on incidence is helpful.12 Too often methodological and quality-control data are not readily accessible. In this instance, the quality-control report identified major issues of concern, only some of which could be addressed. From the point of view of quality, only 11 of the study populations were initially considered acceptable. Remedial work undertaken on an additional seven populations both improved the quality of the data and allowed a larger number of stroke events to be considered in the calculation of incidence and case-fatality rates.
More than 13 500 acute stroke events occurred in these 18 populations in the 3-year period from 1985 to 1987.12 The results confirm that for both men and women, the highest rates are in Russia and Finland, and the lowest rates are in southern and central Europe; the rates are intermediate in Beijing, China. Overall, a threefold difference in incidence rates occurred between countries with the highest rates (285/100 000 and 198/100 000 in men and women, respectively) and countries with the lowest rates (101/100 000 and 47/100 000 in men and women, respectively). Similarly, a threefold difference in case-fatality rate was observed between countries. The 28-day case-fatality rate varied from 15% in men in northern Sweden to 57% in women in the Polish center; the average 28-day case-fatality rate was 30%. A higher case-fatality rate in women than in men was noted in all but two of the populations, which raises important research questions. Despite attention to case-finding procedures, the high rates registered in some countries could be due to the failure to register nonfatal home-treated cases; alternatively, they could be related to a more serious natural history in these populations or even to varying approaches to medical management.
To a large extent the variations in incidence rates reflect the official mortality statistics, but they also demonstrate important discrepancies in the use of routine death certificates for making international comparisons. While in some countries routine death certificate data consistently overestimate the stroke burden, in most countries death certificate data are accurate, at least in the relatively young age group investigated.
The main results of the MONICA Project are yet to come since the study was designed to investigate longitudinal trends within populations and to assess the extent to which these are related to changes in known risk factors. Most of the centers have now completed 10 years of monitoring stroke events and trends in cardiovascular risk factors. The wide range of data gathered in this collaborative study will increase our understanding of the international profile of stroke.
This is the second major international collaborative stroke register. The first, also under the auspices of the WHO, was conducted in the 1970s.14 Unfortunately, these first registers were not maintained, and more than a decade's worth of information has been lost. It is to be hoped that resources and enthusiasm will be available to maintain and extend these more recent efforts to understand the epidemiology of stroke.
An important contribution of the WHO MONICA Project is the development of a standard method that is available for other investigators interested in measuring stroke. The surveillance of cardiovascular disease is a tedious and time-consuming task, but it is essential if we are to monitor efforts to prevent an eminently preventable condition. Only with more detailed information on trends and determinants will it be possible to use limited resources in the most efficient and effective manner. Information from developing countries in particular is needed to ensure that the beneficial trends occurring in most developed countries also occur in developing countries.
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References |
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TopIntroductionReferences |
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1. World Development Report. Investing in Health. London, England: Oxford University Press; 1993.
2. Thom TJ. Stroke mortality trends: an international perspective. Ann Epidemiol. 1993;3:509-518. [Medline] [Order article via Infotrieve]
3. Feinleib M, Ingster L, Rosenberg H, Maurer J, Singh G, Kochanek K. Time trends, cohort effects and geographic patterns in stroke mortality: United States. Ann Epidemiol. 1993;3:458-465. [Medline] [Order article via Infotrieve]
4. Wolf PA, D'Agostino RB. Secular trends in stroke in the Framingham Study. Ann Epidemiol. 1993;3:471-475. [Medline] [Order article via Infotrieve]
5. Broderick JP. Stroke trends in Rochester, Minnesota, during 1945 to 1984. Ann Epidemiol. 1993;3:476-479. [Medline] [Order article via Infotrieve]
6. Ueda K. Epidemiological study on cerebrovascular disease in a Japanese community, Hisayama. J Epidemiol. 1992;2(suppl):S105-S110.
7. Stegmayr B, Asplund K, Wester PO. Trends in incidence, case-fatality rate, and severity of stroke in northern Sweden, 1985-1991. Stroke. 1994;25:1738-1745. [Abstract]
8. Bonita R, Broad JB, Beaglehole R. Changes in stroke incidence and case-fatality in Auckland, New Zealand, 1981 to 1991. Lancet. 1993;342:1470-1473. [Medline] [Order article via Infotrieve]
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Jorgensen HS, Plesner AM, Hubbe P, Larsen K. Marked increase
of stroke incidence in men between 1972 and 1990 in Frederiksberg,
Denmark. Stroke. 1992;23:1701-1704.
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11.
Asplund K, Bonita R, Kuulasmaa K, Rajakangas A-M, Feigin V,
Schaedlich H, Suzuki K, Thorvaldsen P, Tuomilehto J, for the WHO MONICA
Project. Multinational comparisons of stroke epidemiology:
evaluation of case ascertainment in the WHO MONICA Stroke Study.
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Thorvaldsen P, Asplund K, Kuulasmaa K, Rajakangas A-M, Schroll
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mortality in the WHO MONICA Project. Stroke. 1995;26:361-367.
13. Tunstall-Pedoe H. The World Health Organisation MONICA Project (Monitoring Trends and Determinants in Cardiovascular Disease): a major international collaboration. J Clin Epidemiol. 1988;41:105-114. [Medline] [Order article via Infotrieve]
14. Hatano S. Experience from a multicentre stroke register: a preliminary report. Bull World Health Organ. 1976;54:541-553.[Medline] [Order article via Infotrieve]
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