Stroke Mortality Trends in the Population of Klaip ė da From 1994 to 2008

Summary. The objective of the study was to evaluate the trends in stroke mortality in the population of Klaipėda aged 35–79 years from 1994 to 2008. Material and Methods. Mortality data on all permanent residents of Klaipėda aged 35–79 years who died from stroke in 1994–2008 were gathered for the study. All death certificates of permanent residents of Klaipėda aged 35–79 years who died during 1994–2008 were examined in this study. The International Classification of Diseases (ICD-9 codes 430–436, and ICD-10 codes I60–I64) was used. Sex-specific mortality rates were standardized according to the Segi’s world population; all the mortality rates were calculated per 100 000 population per year. Trends in stroke mortality were estimated using log-linear regression models. Sex-specific mortality rates and trends were calculated for 3 age groups (35–79, 35–64, and 65–79 years). Results. During the entire study period (1994–2008), a marked decline in stroke mortality with a clear slowdown after 2002 was observed. The average annual percent changes in mortality rates for men and women aged 35–79 years were –4.6% (P=0.041) and –6.5% (P=0.002), respectively. From 1994 to 2002, the stroke mortality rate decreased consistently among both Klaipėda men and women aged 35–64 years (20.4% per year, P=0.002, and 14.7% per year, P=0.006, respectively) and in the elderly population aged 65–79 years (13.8% per year, P=0.005; and 12% per year, P=0.019). During 2003–2008, stroke mortality increased by 16.3% per year in middle-aged men (35–64 years), whereas among women (aged 35–64 and 65–79 years) and elderly men (aged 65–79 years), the age-adjusted mortality rate remained relatively unchanged. Conclusions. Among both men and women, the mortality rates from stroke sharply declined between 1994 and 2008 with a clear slowdown in the decline after 2002. Stroke mortality increased significantly among middle-aged men from 2003, while it remained without significant changes among women of the same age and both elderly men and women.


Introduction
Public concern about high stroke-related morbidity, mortality, and disability levels has been growing globally. During the last few decades, the routine statistics of cerebrovascular disease mortality have presented different rates in Europe and countries peripheral to Europe. For both sexes, markedly higher rates have been noted moving from west to east, with some exception (1)(2)(3). In the majority of Western European countries, the stroke mortality has signifi cantly decreased during the last decades (4)(5)(6). The death rate from cerebrovascular diseases in the majority of Central and Eastern European countries also decreased in the 20th century, and this rate remains markedly higher compared with Western countries (1)(2)(3). It is estimated that the population aged more than 65 years will make up 35% of the whole population in Europe by 2050, and this will be a serious challenge to health care systems of all nations (7).
Epidemiological stroke research carried out in Lithuania indicates that Lithuania is a country with an increased stroke risk. An epidemiological study recently carried out in Kaunas on the basis of the WHO MONICA project has revealed a different trend in stroke mortality during 1986-2002 in the middle-aged population: a decrease in the mortality rate from ischemic stroke and intracerebral hemorrhage in women and an increase in the mortality rate from all types of stroke and ischemic stroke in men (8).
The objective of the present study was to evaluate stroke mortality trends in the population of Klaipėda aged 35-79 years from 1994 to 2008.

Material and Methods
Mortality data on all permanent residents of Klaipėda aged 35-79 years who died from stroke during 1994-2008 were gathered for the study. The offi cial mortality statistics data for 1994-2008, obtained from Klaipėda Civil Registration Offi ce, were used for the mortality analysis. All the death certificates (statistical form No. 106/a) that were fi lled in and coded by the physician certifying the death were checked for the permanent population of Klaipėda. The International Classifi cation of Diseases, the 9th revision (ICD-9, codes 430-436), was used for the period 1994-1996, and the 10th revision (ICD-10, codes I60-I64) was used for the period 1997-2008.
The annual population counts for the denominators were obtained from the statistical department of Klaipėda city. The stroke mortality rates per 100 000 population of Klaipėda were evaluated. The age-adjusted mortality rates were calculated using the Segi's world population for direct standardization. The 95% confi dence intervals were calculated in respect of the Poisson distribution of the events within the age groups. Data for men and women were analyzed separately.
Initially, scatterplots opposing mortality rates and calendar years were built in order to better visualize the function that might better express the relationship between these variables. Exponential or low-degree polynomial models were expected to fi t better to the mortality rate. As a measure of the model precision, the coeffi cient of determination (R 2 ) was used. Nevertheless, the aim of the presented analyses was to look for an increase (or decrease) in the rates. Trends were analyzed using the method of linear regression on logarithms of the age-standardized annual rates. The regression coeffi cient multiplied by 100 was used as approximated annual percent change, which is presented in this article. Confi dence intervals (CI) for the coeffi cient b from the regression models were used to estimate confi dence intervals for annual percent change in mortality.
The linearity assumption for the annual percent change was tested by visual inspection and by calculating the R 2 for different models. During the entire study period (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008), a marked decline in stroke mortality with a clear slowdown after 2002 was observed. Signifi cant changes in the trends were identifi ed, the observed period was divided, and the annual percent change was calculated for the two periods: from 1994 to 2002 and from 2003 to 2008. Mortality rates and trends were calculated for 3 age groups (35-79, 35-64, and 65-79 years).

Discussion
Our study showed high age-adjusted stroke mortality rates in Klaipėda city compared with Western countries: during the fi rst year of the study (1994), the mortality rate in men aged 35 to 79 years was 251.  (11).
From the global perspective, Eastern European countries (republics of the former Soviet Union and Bulgaria) are in the leading position in stroke mortality; meanwhile, Switzerland and the United States are the countries with the lowest stroke mortality rate, which is 8 times lower compared with the postsocialist countries of Europe (9,11,12).
The epidemiological study showed a decrease in cardiovascular and other-cause mortality in Eastern Europe during 1990-2000. Overall, this decrease started about 25 years later compared with Western European countries (2). During the study period, stroke mortality rates decreased rapidly in Western European countries; in the Unites States from 1997 to 2007, the annual stroke death rate decreased 34.3%, and the actual number of stroke deaths declined 18.8% (13). The stroke mortality in England during 1979-2004 showed a steady and consistent decline without any slowdown trends for the last 25 years (6). The Oxford Vascular Study reported a decrease in stroke mortality during 1981-2004 (14). Finish researchers indicated a decreased mortality from all types of stroke for both sexes and all age groups (15). In Poland, stroke mortality rates were continuously increasing, but the sharpest increase was observed between 1991 and 2000. In Hungary, the stroke mortality rates did not show a clear trend until 1993 and, thereafter, declined by >2% per year. In the Baltic States, the stroke mortality rate declined by ∼30% between 1993 and 2000 (2). The decline in stroke mortality for the period of study has been also stated by other authors (5,16). However, the decline has slowed greatly in recent years. In our study, the greatest slowdown in the declining trend was seen from 2000.
Analysis of stroke mortality by sex revealed a higher mortality rate among men; however, the difference in older age groups was less signifi cant. Similar fi ndings have also been reported by other authors (11). Moreover, our study showed that between 1994 and 2002, the decline in stroke mortality rates in men was greater than that in women (2,13). Other epidemiological studies stated that sex differences in stroke mortality were present in the countries where the stroke mortality rate was high (>200 per 100 000 population); however, in the countries with a lower stroke mortality rate (<100 per 100 000 population), the difference in mortality rates between sexes was signifi cantly lower (17). The causes of these differences are complex, but this may be explained by different trends in smoking behavior in men and women (2,13) or by characteristic features of hormone balance; research investigating the sexual dimorphism of stroke is only in its early stages (18).
Numerous studies have given various causes for the decrease in the mortality rate: improved socioeconomic conditions and, therefore, higher-quality stroke prevention and decreased morbidity (5,19); decrease in stroke severity over time in part explaining the decrease in the fatality rate at 1 month after onset (20); better quality of stroke treatment management, better acute stroke treatment, and the decrease in early case fatality (21). Having analyzed cardiovascular and other death causes in Western and Eastern Europe, the authors have stated that among causes of cardiovascular disease-related death, the changes in nutrition and improved treatment of the diseases play a major role (2).
During the second study period (2003)(2004)(2005)(2006)(2007)(2008), the results showed an increased stroke mortality rate among middle-aged (35-64 years) men in Klaipėda. The epidemiological survey using the WHO standardized methodology carried out in Kaunas during 1998-2002 reported very similar fi ndings. The causes of the stroke mortality increase in middleaged men were not revealed, since during the period of study, there were no signifi cant changes in classical risk factors for stroke observed among men (22); therefore, the authors suggested that the increase in stroke mortality could have been caused by other, nonclassical, stroke risk factors, e.g., psychosocial or socioeconomic changes (8). Research data obtained by other authors indicated that economic conditions, increase in alcohol consumption, or depression infl uenced the mortality from heart diseases and strokes (19,21,23). Another survey, which was carried out by employing offi cial data of the mortality registry in Kaunas region, also reported the increase in stroke mortality in men and women aged 25-64 during 2000-2004 (24). The authors did not indicate the causes of increasing mortality rates during the study period.
The prevalence of the major cardiovascular risk factors in Klaipėda city has not been studied yet; therefore, the factors that caused a signifi cant increase in stroke mortality in men aged 35-64 during 2003-2008 can only be presumed. As the development of the Lithuanian economy shows, the economic indices during the study period till 2008 were improving; however, the increase in the stroke mortality rate in Klaipėda necessitates comprehensive analysis of the related causes and poses new chal-lenges to the city community and health professionals.
The epidemiological survey on the lifestyle risk factors carried out in Lithuania during the last decade revealed that habits of our citizens were not favorable to health (25): smoking epidemics reached the "maturity" stage, and the number of smokers was presumed to grow (26); the high level of hypercholesterolemia was observed (22); and the nutrition of men was found less corresponding to the healthy eating recommendations than that of women (27). It was also stated that overweight in the male population increased (28), and though alcohol intake remained rather stable, beer consumption increased (29). According to the study on risk factors in Kaunas, arterial hypertension, smoking, and increased malondialdehyde concentration in blood serum during the last decade have significantly increased the risk of mortality from stroke in elderly men (30). Considering these data, it can be presumed that stroke risk profi les in Klaipėda and Kaunas are alike; therefore, the factors causing stroke mortality could be similar. Thus, in order to develop medical care for cerebrovascular patients in Klaipėda, it is recommended to improve the quality of primary and secondary stroke prevention, especially for a middle-aged male population, in the nearest future.

Conclusions
Among both men and women, the mortality rates from stroke strongly declined between 1994 and 2008 with a clear slowdown in the decline after 2002. Stroke mortality increased signifi cantly from 2003 among middle-aged men, while it remained without signifi cant changes among women of the same age and both elderly men and women.

Statement of Conflict of Interest
The authors state no confl ict of interest.