Epidemiology of Stroke in Kaunas, Lithuania
First Results from the Kaunas Stroke Register
Background and Purpose In Lithuania, only routine mortality statistics have thus far provided data on the epidemiology of stroke. This study aims to assess the mortality, incidence, and case-fatality rate of stroke in the city of Kaunas, Lithuania, during 1986 to 1988.
Methods A community-based stroke register was set up in 1986 to collect data on all suspected events of acute stroke that occurred in the population aged 35 to 64 years permanently residing in Kaunas. Crude and age-standardized attack rates, incidence, mortality, and case-fatality rates were calculated for the period studied.
Results Among men, the average age-standardized incidence of stroke (referring to first-ever events) was 230/100 000, the attack rate (all events) was 300/100 000, and the mortality from all strokes was 68/100 000. Among women, the corresponding rates were 131/100 000, 154/100 000, and 35/100 000, respectively. Of 973 acute stroke events registered, 80% were first-ever strokes. The age-adjusted 28-day overall case-fatality rate and the case-fatality rate of first-ever stroke were 23.3% and 19.8% in men and 21.8% and 21.3% in women, respectively.
Conclusions The findings from this first assessment of the incidence and mortality of stroke show that in the mid-1980s both were high in Kaunas compared with other countries. The case-fatality rate was similar to that reported for most other European countries. Further investigations are being carried out to assess the trends in mortality, incidence, and risk factors of stroke in the Kaunas population.
In most western European countries, the United States, Australia, New Zealand, and Japan, stroke mortality has steeply decreased during the last two decades.1 2 At the same time no improvement or even an increase in stroke mortality has been reported in many eastern European countries.2 3 On the other hand, the reliability of mortality statistics regarding stroke has been questioned, particularly in the eastern European countries.4 It has been difficult to determine the magnitude of the health problems related to stroke in eastern Europe because reliable epidemiological data on stroke are scarce in these countries. Thus far there has been no proper assessment of the occurrence of stroke in the Baltic country of Lithuania, which regained its independence recently.
In the early 1980s Kaunas joined the World Health Organization (WHO) MONICA (Monitoring of Trends and Determinants in Cardiovascular Disease) Project, an international collaborative study whose main target is to “measure the trends in cardiovascular mortality and coronary heart disease and cerebrovascular disease morbidity and to assess the extent to which these trends are related to changes in known risk factors, daily living habits, health care and major socioeconomic features measured at the same time in defined communities in different countries.”5 To reach this goal, 39 centers in 26 countries established a system to register cases of myocardial infarction, and 19 centers also started a stroke register. Kaunas, the second largest city of Lithuania, established a stroke register in 1986.
We report here the results from the first 3 years of stroke registration, 1986 to 1988. Stroke incidence, attack rates, mortality, and case-fatality rates during this study period are described and discussed.
Subjects and Methods
Kaunas, an industrial city with emphasis on textiles, manufacturing, and the food industry, is located almost in the center of the state (Fig 1⇓). Kaunas contains three general hospitals and one university hospital, which has a specialized neurosurgical department.
Of the 430 000 inhabitants living in Kaunas, more than 90% are ethnic Lithuanians. The Kaunas Stroke Register includes events that occur in the population aged 25 to 64 years. The source of the population data is the Central Statistical Department of the city of Kaunas, which reports the population size in 5-year age groups every year. The structure of the population for the study period in regard to age and sex is shown in Table 1⇓. The population aged 25 to 64 years increased almost 7% in 3 years, mainly because of immigration from the rural areas to the city.
The “cold pursuit” technique is used to identify acute stroke events. The events are found retrospectively, abstracting information from medical records, death certificates, and other possible sources. When compared with the “hot pursuit” technique, this method has a higher possibility of missing some stroke events, particularly nonfatal events. Incomplete coverage mainly occurs in the case of patients treated at home. However, home treatment of acute stroke patients is rare in the group aged 25 to 64 years in Kaunas. In the first year of stroke registration, great efforts were made to find all the stroke cases.6 Less than 5% of all nonhospital stroke patients aged 25 to 64 years were not treated in the hospital, but this proportion is likely to be higher in older subjects. This was one of the reasons why it was decided not to register strokes occurring in people aged 65 years or older in Kaunas.
The main sources used to identify acute stroke events are hospital discharge records, patient registration books (kept in some neurological, neurosurgical, and intensive care units), records of domiciliary care of outpatient departments, death certificates, and necropsy and medicolegal records. These sources are reviewed every 3 months except death certificates, which are reviewed every month. All hospital discharge records coded as rheumatic heart disease (International Classification of Diseases, 9th Revision [ICD-9]7 codes 390 to 396), hypertension (ICD-9 codes 401 to 405), and cerebrovascular disease (ICD-9 codes 430 to 438) are checked to determine eligibility for entry in the stroke register.
All suspected acute stroke events are recorded on special forms translated from the Stroke Event Registration Form of the WHO MONICA Project.5 One person (D.R.) from the Institute of Cardiology of Kaunas Medical Academy retrieved and coded the data for the entire study period.
During the period studied, several checks were made to ensure the quality of the database. Each year a coding standardization exercise was performed. International stroke test case histories were circulated among all MONICA collaborating centers, including Kaunas, and the coding results of these exercises were analyzed by the MONICA Quality Control Center for Event Registration,5 which gave feedback information to the local centers, including Kaunas, on the quality of their performance.
Computerized checks were also made, both locally in Kaunas and in the MONICA Data Center (located in the National Public Health Institute of Helsinki in Finland). These checks included an evaluation of the completeness of the stroke register forms, the correctness of recorded values, and the internal consistency between variables related to the same topic.
Definition of Stroke
According to the WHO MONICA protocol, stroke is defined as “rapidly developed clinical signs of focal (or global) disturbance of cerebral function lasting more than 24 hours (unless interrupted by surgery or death) with no apparent cause other than a vascular origin.”5 Global symptoms apply only to patients with deep coma or subarachnoid hemorrhage without focal neurological signs.
Every stroke event must have its apparent onset within the study period and more than 28 days from any preceding recorded coronary or stroke event in the same subject. If subsequent attacks occur within 28 days from the onset of the first acute symptoms, they are not counted as separate. After 28 days, new events in the same subject are registered as different attacks and are classified as recurrent stroke events. A stroke event is defined as fatal if the death occurred within the first 28 days from onset. If the patient is alive after 28 days from the onset of the attack, the stroke is classified as nonfatal.8
As required by the MONICA protocol, all suspected stroke events are classified into four categories: definite stroke, no stroke, definite stroke associated with definite myocardial infarction, and insufficient data. The diagnostic category “insufficient data” is mainly used for fatal cases, such as sudden death without necropsy. Living patients are classified in this category if there is no documented history of focal neurological deficits and no other diagnosis, if it is impossible to determine whether the symptoms are from stroke or from some other disease (eg, epilepsy), or if clinical findings otherwise typical for a stroke are presented but the duration is uncertain.
During the study period the ICD-9 was used.7 Only ICD-9 codes 430 (subarachnoid hemorrhage), 431 (intracerebral hemorrhage), 433 (cerebral infarction due to thrombosis of precerebral arteries), 434 (cerebral infarction due to thrombosis or embolism of cerebral arteries), and 436 (unspecified type of stroke) are accepted diagnoses for acute stroke in the WHO MONICA Project.8
In this report the incidence rate refers to the rate of first-ever events, ie, those that occur without evidence of a previous stroke. The attack rate refers to the rate of all episodes of stroke (first and recurrent events together). Mortality from stroke was calculated for all events and for first-ever events separately. The case-fatality rate refers to the proportion of stroke patients who died within 28 days from onset of symptoms of acute stroke and was calculated for both all and first-ever strokes.
During the 3 years studied, 18 registered stroke events (1.9%) were classified as “no stroke” and were excluded from the present analysis.
All the rates presented were age-standardized by the direct method; Segis’s age distribution of the world population was used as the standard.9 The case-fatality rate was age-adjusted by means of weights proposed for use in the WHO MONICA Project. The weights were derived from the age distribution of coronary and stroke events in pooled MONICA populations: 1, 3, 7 for the age groups 35 to 44, 45 to 54, and 55 to 64 years, respectively. Because the number of events in the group aged 25 to 34 years was very small, this age group was not included in the age-standardized rates. The 95% confidence intervals for the rates were calculated assuming the Poisson distribution for the events within these age groups. Differences in rates at the P<.05 level, using a two-tailed test, are reported as statistically significant.
During the study period, 973 stroke events were registered: 583 (60%) in men and 390 (40%) in women (Table 1⇑). Of them, 779 (80%) were first-ever stroke events, and 194 (20%) were recurrent stroke events. The proportion of recurrent stroke events tended to increase with age, and it was higher (P=.004) in men (23%) than in women (15%). Of the 973 strokes registered, 23% were fatal within 28 days from onset. The average rates for the 3 years together are presented here because of the relatively small number of stroke events in different age groups.
As shown in Table 2⇓, nearly 95% of all stroke patients were examined by a neurologist and almost 90% by a physician. Cases of suspected acute stroke without consultation of a neurologist or a physician were mainly sudden deaths. On average, only 1 in 30 stroke patients was examined by a computed tomographic scan and 1 in 18 by angiography. The average rate of necropsy performed was high, at 76%.
The incidence and attack rate of stroke increased steeply with age in both men and women (Fig 2⇓). The increment between the youngest and the oldest age groups was eightfold. Both the incidence and the attack rate of stroke were higher among men than among women in all age groups. The male-to-female ratio was 1.8 for incidence and 2.0 for attack rate (Table 3⇓). Among men the attack rate was 23% to 24% higher and among women 11% to 16% higher than the incidence of stroke (Fig 2⇓). Mortality from stroke was approximately twice as high in men as in women, and the male excess in mortality from first-ever strokes was approximately 50% (Table 4⇓).
The case-fatality rate was approximately twice as high in men (22% for all strokes and 29% for first-ever strokes) as in women (12% and 14%, respectively) in the group aged 35 to 44 years; for first-ever strokes there was an opposite trend after the age of 45 years (Table 5⇓). The case-fatality rate of first-ever strokes tended to be lower than that of all strokes among men but not among women.
In this report we presented for the first time the occurrence of stroke in the middle-aged population of Kaunas. Until 1986, information about the occurrence of cerebrovascular disease in Lithuania was based only on official mortality statistics. According to these data, a sharp upward trend in stroke mortality as well as in ischemic heart disease mortality6 10 11 12 was observed in Lithuania during the last two decades, similar to what has been observed in many eastern European countries in general.2 At the same time we reported an increasing trend in coronary heart disease in Kaunas.12
Adequate coverage of all suspected stroke cases in the population is necessary to estimate the incidence and attack rates of stroke in a reliable way. During the first year of stroke registration (1986) in Kaunas, efforts were made to assess the frequency of stroke cases treated at home. It was found that more than 95% of all patients with nonfatal acute stroke aged 25 to 64 years were treated in the hospital.6 It was also found that the vast majority of patients who were treated at home during the first 28 days of onset of stroke were hospitalized later (D.R. et al, unpublished data, 1991). Thus, by abstracting information from hospital discharge records, domiciliary care records of outpatient departments, and death certificates, we estimate that we found nearly all stroke cases in the population aged 25 to 64 years, with a possible loss of 0.5% to 1.0% of acute stroke cases. In addition, we have permanent contacts with the chiefs of the neurological departments of the hospitals and of the outpatient departments. By cross-checking our stroke register data with the data on the stroke cases treated in these hospital departments or by physicians visiting the patients at home, we were able to minimize the incompleteness of the case ascertainment of acute stroke events in Kaunas. In addition, the quality control assessment of the stroke registration performed by the MONICA Data Center recently determined the Kaunas Stroke Register data to be of good quality (K. Asplund et al, unpublished data, 1994).
According to the requirements of the MONICA protocol, classification of stroke events into the different subcategories is based on results from brain computed tomography and/or angiography and/or necropsy (in case of death). Unfortunately, the proportion of computed tomographic scans and angiography performed was very low (on average 10% and 17%, respectively). Despite the fact that the average rate of necropsy performed was high (76%), it was not possible to analyze the incidence of stroke by subcategories in the Kaunas Stroke Register. In fact, given the low proportion of diagnostic examinations performed in nonfatal stroke, more than 70% of all strokes and 87% of nonfatal strokes were assigned to the subcategory “unspecified type of stroke” (ICD-9 code 436) following the strict criteria of the MONICA Stroke Study.5 8 Nevertheless, the high autopsy rate will allow us to perform the analysis on mortality of different stroke subtypes.
There were no significant discrepancies between the mortality data for stroke based on the official statistics and on the Kaunas Stroke Register.6 This was not unexpected, because the autopsy frequency was high in cases of fatal stroke. Thus, information on death certificates concerning stroke seems to be of satisfactory quality in Kaunas, unlike that reported from many other countries.4 An analysis by the WHO MONICA Project comparing the official mortality statistics among the populations participating in the MONICA Project showed that in 1984 Kaunas had intermediate stroke mortality in women aged 35 to 64 years, whereas mortality from stroke in men was very high.13 Mortality from stroke in men and women in Kaunas observed during 1986 to 1988 places Kaunas among those MONICA centers with the highest stroke mortality.
The incidence of stroke among the population of Kaunas aged 35 to 64 years was higher than that reported in many other countries. In both men and women the incidence was similar to those reported from North Karelia (Finland)14 and Copenhagen (Denmark)15 but higher than the rates observed in Auckland (New Zealand),16 Söderhamn (Sweden),17 or Rochester, NY.17 The incidence of stroke reported from Poland,18 which is a neighbor of Lithuania, seems to be slightly lower than that we report for Kaunas. In 1985, in the Poznan district of Poland the incidence of stroke was 25/100 000 in men aged 30 to 39 years, 110/100 000 in men aged 40 to 49 years, and 383/100 000 in men aged 50 to 59 years. In women the rates were 15/100 000, 55/100 000, and 148/100 000, respectively. On the other hand, the incidence of stroke in Dijon (France)19 and in China20 21 was higher than that in Kaunas. In the present study the incidence rose steeply with increasing age, a typical finding observed in many other studies. The case-fatality rates observed in the Kaunas population were similar to those reported in other countries.16 19 22
Overall, the outlook regarding the incidence and mortality of stroke in Kaunas does not look promising because both are quite high, especially in men. One possible explanation for this finding may be the high levels of cardiovascular risk factors observed in the population of Kaunas. According to data from the first risk factor survey that was performed in Kaunas during 1983 to 1984, among all MONICA centers Kaunas had the highest body mass index in both men and women.23 Diastolic blood pressure was also among the highest, and almost one third of the population had hypertension. The mean levels of the known cardiovascular risk factors were similar among men and women, except for the prevalence of current smokers, which was 42% among men and only 5% among women. This difference may be one of the reasons for the twofold difference in attack rate and mortality of stroke observed between men and women in Kaunas. There is increasing evidence that smoking is a risk factor for stroke.24 25
Our results indicate the need for further investigations of trends in stroke incidence and related risk factors in Kaunas. Such analyses are needed to define which kind of primary prevention activities are required to reduce stroke occurrence in Kaunas. This is a major challenge for preventive medicine during the difficult period of rebuilding the Republic of Lithuania.
This study was supported by a grant from the Center for International Mobility (CIMO). Special thanks go to Anna-Maija Rajakangas for preparing Fig 1⇑.
- Received September 12, 1994.
- Revision received November 7, 1994.
- Accepted November 8, 1994.
- Copyright © 1995 by American Heart Association
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