Published online before print August 21, 2003, doi: 10.1161/01.STR.0000091270.29127.1E
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(Stroke. 2003;34:2107.)
© 2003 American Heart Association, Inc.
Original Contribution |
Editorial Comment—Stroke Incidence and Quality Standard for Comparison
Department of Public Health, Aichi Prefectural College of Nursing and Health, Nagoya, Japan
Stroke is one of the leading causes of death in many countries. Accordingly, the frequency of occurrence of stroke provides essential information when planning community-based programs intended for reduction of mortality. In epidemiology, incidence is widely used as the measure of the frequency of occurrence in populations. The measure is potential of community-based studies to answer additional questions based on an unbiased sample of incident cases when understanding disease etiology. In addition, the incidence also measures the density of events occurring during the observation period. Because the differences in registration procedures, case ascertainment, and diagnostic procedures1 could result in inaccurate measure of incidence, more accurate ascertainment of the incidence is required. It needs to define clearly for whom and what it uses when measuring the incidence. If it applies to stroke, the numerator should use the individuals defined by characteristic and background who met the standardized criteria of stroke (including stroke subtypes), and denominator should use those who become ill (ie, population at risk).
Recently, stroke incidence has ranged widely among reports from different regions of the world and at different points in time using community-based stroke studies and cohort studies in many countries.2–12 Among these reports, there was no research for which the same diagnostic criteria, diagnostic method, and population denominator were used. Comparison of stroke incidence is only meaningful when based on the same diagnostic criteria and procedures in various parts of the world. Definitions (standard criteria) and methods must be standardized for comparison.
In the early 1980s, the WHO MONICA (World Health Organization Monitoring Trends and Determinants in Cardiovascular Disease) project was initiated to continuously register the occurrence of stroke and myocardial infarction among many populations by use of uniform procedures and methods in 16 European and 2 Asian populations. Briefly, the protocol for the stroke registers provided detailed instructions for event registration. It included guidelines for case ascertainment, outlined validation procedures, and gave specific coding rules for diagnostic category (definite stroke, unclassifiable, or not stroke), order of event (first or recurrent), and case-fatality rate. Diagnostic criteria were applied to symptoms, clinical findings, and investigations undertaken within 28 days of onset.13
WHO MONICA provides the most reliable and multinational compatible information on stroke incidence and case fatality by using stroke registers, which can provide more accurate estimates of incidence and mortality rates than official routine statistics can.14 In addition, suspected stroke events could be also classified through strictly standardized methods and criteria.
Several studies have compared a population-based MONICA stroke registry with hospital discharge registry. According to Asplund et al,15 compared using the ratio of the number of fatal stroke events in the MONICA registers to the number of stroke deaths in routine mortality statistics, a MONICA stroke register-to-routine mortality statistics ratio <1.0 and 
1 were found in 10 of the 21 populations. This indicates that the official statistics may greatly underestimate or overestimate stroke mortality in many other areas. In Swedish16 and Finnish17 MONICA populations, moreover, 10% to 13% false-positive and 14% to 17% false-negative cases were found in the routine vital statistics. The proportion of false-negative in nonfatal cases was slightly lower in the population-based MONICA registry (4%) than in hospital discharge registry (6%) and in official mortality statistics (17%).16 Stegmayr et al18 stated, "The quality of official mortality data varies between countries because of different traditions and levels of reliability in assigning the cause of death and because autopsies are not always performed. Data based on the uniform registration procedures are likely to give more reliable information about the total burden of stroke among populations."
This study provided some interesting information on epidemiological features of stroke in South America. First, this study is a review based on published evidence of epidemiological features of stroke in South America. Because data used in this study was selected on the basis of prepared inclusion criteria, it appeared that reliability and comparability among selected studies of the results are high enough. Second, most knowledge on stroke has mainly focused on Eastern Europe and Northern America. There is very little known about the peculiarities of stroke in South America. To the best of our knowledge, this is the first study that has systematically examined the epidemiological characteristics of stroke in South America. Accordingly, the findings that both the prevalence and incidence of stroke were lower in South America than in developing countries are meaningful for identification of the etiologic factors of stroke.
Third, the study revealed a higher percentage of patients with intracranial hemorrhage among stroke compared with other countries,19–21 although the pattern of stroke subtype did not differ. A higher proportion of stroke patients with arterial hypertension was also observed. Moreover, marked differences in the pattern of stroke subtype and risk factors other than hypertension were also observed among ethnicities and countries.
This study provides important findings toward increasing knowledge of the epidemiology of stroke and subsequently leading to a plan for prevention programs of stroke in South America.
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