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SOFIA HEART STUDY: UNEXPLAINED PROBLEM OF CHD RISK

Author: Elena Shipkovenska

Editor's Note: We need to clarify a couple of issues, notwithstanding. The Sofia Heart Study (SHS) comes to designate the so-called unreferenced MONICA study for Bulgaria — cf., "Ivanov, L. Prophylaxis of Non-communicable Diseases. Sofia, 1988", "Merdjanov, Ch. One Compromised Leadership. Sofia, 1995", etc. about further dilemmas of chronic disease prevention in this country. MONICA: MONItoring of trends and determinants in CArdiovascular disease, was considered to be an approach-oriented study of WHO based on protocols developed in the 1960s and 1970s. More than 50 countries participants were invited, but only 20 candidacies met the inclusion criteria, some of them forming two or more cohorts. Thus Bulgaria applied but didn't qualify for MONICA. The observer status was granted with limited pre-conditions and this constituted a baseline for the "Sofia Cohort". The devaluation of data and general flaws in methodology, study design, cost-effectiveness, etc. had been discussed manifold in the international literature for WHO-MONICA. The case for Bulgaria has remained conundrum — at least, in the eyes of local health authorities — and, there still persist the illusion that chronic disease prevention was being done in the country. Authorship and publication of this monograph was completed by Prof. E. Shipkovenska. The bulgarian copy of the book is widely accessible, however, it has the inherent backdrop of translation errors and terminological inadequacies, ditto.

 

1.3.4 Current knowledge about risk factors for cardiovascular diseases in Bulgaria

1.3.4.1 Primary data sources

The scientific environment in Bulgaria was not suitable for public health research programmes directed towards chronic diseases in the last decades. However many small studies have been undertaken by various departments and organizations in the country.

Most of these reports are not published in international refereed journals, but they contribute to the knowledge about the public health policies and health behavior of the community. Moreover they are the only source of such information.

No national system of repeated risk factor surveys has been instituted in Bulgaria. Several risk factor surveys have been conducted, but the credibility of their reported findings has not been established by adequate description of their methods.

(See below).

Such sources as are available all have serious limitations. These are summarized in Table 1.13.

 

1.3.4.1.1 Bulgarian CINDI Survey

CINDI stands for "countrywide integrated non-communicable disease intervention" programme and was coordinated by the World Health Organization, European Office. Bulgaria was included in this programme and as part of it, in 1984, 711,000 persons, from four adjacent regions - Gabrovo, Sliven, Veliko Tarnovo and Stara Zagora were screened for chronic diseases risk factors. Information about smoking habits and practices related to salt consumption were obtained by interview. In addition height, weight and blood pressure were measured. No reports have been found of eligibility criteria, sampling procedure, recruitment methods and participation rates. However, it is common knowledge among informed persons in Bulgaria that measurement protocols were poorly developed and were not effectively implemented. The findings of this study have been reported in an unsystematic manner, and are still appearing.

In 1994 Bulgaria again participated in CINDI with 2363 persons from the age group 25-64 living in the region Veliko Tamovo being surveyed. The methodology and findings of this study were recently published in Health Promotion Bulletin of the National Centre for Health Knowledge.

 

1.3.4.1.2 Sofia Risk Factor Study I

This is the name I shall employ to describe a study conducted during the period 1988-1990 by Ch. Nachev, E. Shipkovenska (Higher Medical Institute, Clinic of Internal Diseases), F. Ribarova, S. Shishkov (National Centre of Hygiene, Ecology and Nutrition), on a sample of 1154 persons aged 15-64 years in the capital Sofia. The stated aims were: to measure the distribution of blood pressure, the frequency of arterial hypertension among the population of Sofia, to characterize the average daily food intake with special emphasis on lipids and proteins and to assess association between nutrition and hypertension. The investigators measured height and weight and performed electrocardiogram (ECG), and physical examination on each participant. In addition they took blood samples to measure cholesterol. A food frequency questionnaire was included.

So far, no written description of the sampling methods or measurement protocols of this study has been located. Graphical presentations have been prepared of some of the findings.

 

1.3.4.1.3 Sofia Risk Factor Study II

This is the name I shall employ to describe a study conducted by Ch. Nachev and E. Shipkovenska from Higher Medical Institute, Clinic of Internal Diseases. The study was carried out in 1992 on a sample of approximately 1000 persons aged 15 - 64. Out of the total of 27 polyclinics in Sofia, the sample was chosen from 25. No written report has been found of sampling methods and participation rate.

The aim of the study was to measure changes in risk factors through the transition period in order to compare them with mortality changes. Graphical presentations have been made of some of the findings.

 

1.3.4.1.4 Case-control study for risk factors for IHD

The case-control study was carried out in Central clinical hospital, Sofia, in 1994. Cases (n = 260) were patients aged 45 to 69, with confirmed diagnosis of IHD, admitted to the cardiology unit and controls (n = 250) were patients admitted for minor elective surgery. Measurements were made of blood pressure, height and weight and a blood sample taken around 3 days after admission. Subjects were invited before discharge and asked about the frequency with which they consumed fresh foods, their smoking and drinking habits and physical activity. The detailed methodology and results were presented and published elsewhere.

Although not a surveillance study, risk factor distribution in the controls could be suggestive of community levels.

 

1.3.4.1.5 Multistage nationwide survey 1997

Multistage nationwide survey was conducted in May 1997 and designed to be representative of the population of Bulgaria aged 18 years and older. A two-stage random sampling procedure was used. 1550 persons were interviewed face-to-face. The questionnaire collected data on a range of variables related to lifestyle, health status, household income, and socioeconomic status, use of health services and total expenditure of health care. The detailed methodology and results from multivariate analysis of data on patterns of tobacco smoking and alcohol consumption and their relationship with socio-demographic factors were published elsewhere.

 

1.3.4.1.6 Dietary data survey

Apart from the above sources this comes from National food balance sheets and from diet surveys on specific populations. The national household budget survey system was established in 1951 and the surveys have been conducted annually by the National Institute of Statistics since 1953. The surveys cover whole country, the urban and rural population and the major socio-economic strata. At present, 2508 households are selected randomly through a two-stage sampling procedure from 271 urban and 147 rural settlements. The quantities of purchased, home-produced or bartered foods, as well as foods consumed away from the household, are recorded all the year (National Institute of Statistics, 1995).

National food balance sheets are known to be prepared for Bulgaria but apparently have not been published regularly. They are based on the collecting reports of the FAO. Such sheets attempt to estimate the amount of food “disappearing” for human consumption. They provide very indirect and crude measure of consumption. They tend to overestimate actual consumption, because do not consider the amount of the food thrown away or used as a food for dogs, cats etc.

Nation-wide nutrition surveys were conducted throughout Bulgaria in April - May 1997 and March 1998 by the National Centre of Hygiene, Medical Ecology and Nutrition with GALLUP-BBSS. Sampling used a multistage random probability design with quotes for age-sex groups. The effective sample comprised 2757 respondents, demographically representative for the Bulgarian population over 1 year of age. Respondents with urban residence were 69.1%; males were 49.5% within the studied sample. Pregnant women were not included and will be a subject of special survey.

Data were obtained by in-house face-to-face interviews. Information for major socioeconomic characteristics of the responders’ households was collected. Dietary data were obtained using 24-hour recall. All days of the week were proportionally included and in this way any day-of-the-week effects on food and /or nutrient intakes were taken into account. The quantities of foods consumed were determined by description of foods and beverages consumed in household measures or average portion size.

 

1.3.5 Shortcomings in available risk factor evidence for Bulgaria

Risk factor studies conducted so far in Bulgaria suffer from the following limitations:

1.3.5.1 Study populations

None of the studies carried out before 1994 reported any of the following: clear definition of eligible source population, sampling frame employed, methods of sampling; recruitment procedures and participation rates. Hence the representativeness of the study populations is uncertain.

1.3.5.2 Data collection

For data obtained by interview, the methods of interview and data collection are important elements in a surveillance study. They could be sources of random and systematic errors due to the interviewer, the respondent, data coding and processing. Most of the studies conducted in Bulgaria suffer from lack of detailed description of these procedures. For data obtained by measurement (anthropometric data, blood pressure, blood constituents) measurement protocols have typically not been reported and nor have the results of the quality control procedures.

1.3.5.3 Interpretation of results

The inadequacies explained in the above two sections raise serious questions about the validity and generalisability of the results coming from these studies.

 

1.3.6 How Sofia Heart Study differs from the rest of Bulgaria

It is important to what extent the conclusions drawn from SHS are going to be valid for the whole of Bulgaria. The differences in various characteristics of Sofia and the rest of Bulgaria can affect the generalisability of the results.

In 1994 Sofia had a population of 1,188,563, which was about 14% of the population of Bulgaria (8,443,600). The male population in the city of Sofia was 48.5%, while the proportion of male population for whole country was 49.0%.

Age structure of the population of Sofia had the same tendency of a higher proportion of people in older age groups and a lower proportion of population in the younger age groups, as in the rest of Bulgaria. For example, in the age group over 60 the proportion is 19.2% for Sofia and 20.5% for the whole country.

The structure of the population according to the marital status in the city of Sofia was close to that of Bulgaria. The biggest difference was in the proportion of married people, which was with 4% lower in Sofia (50.9%) than the whole country (549%).

At the end of 1994, 62.6% of the population of Sofia had eleven or more years of education, while for the whole country this proportion was 41.3%. The observed difference is due mainly to migration process and the stable tendency of aging of the rural population. Another important reason is the fact that Sofia as the administrative and political center of Bulgaria attracts people with high levels of education.

The proportion of unemployed people in Sofia was 5.3%, while for Bulgaria this percentage was 12.8% in 1994.

The supply with health care in Sofia is better than in the rest of the country. In Sofia there are 24 medical doctors per 10 000 people, while in the whole country there are 22 / 10 000. In primary health care the difference is even bigger, 9.6 physicians per 10 000 population for Sofia and 5.1 / 10 000 for Bulgaria. Additionally, there is higher concentration of specialists in Sofia than in the rest of the country.

The crude mortality rate from cardiovascular diseases is more than two-fold higher in rural (1351.0 / 100 000), than in urban areas (638.4 / 100 000) of Bulgaria. As there are no data available about age standardized rates one does not know how much of the difference is an artifact of age structure. Additionally, insufficiency of specialists in rural areas could reflect in incorrect registration of unclear conditions as CVD mortality. Presumably however, the age standardized mortality rates of vascular diseases in Sofia are lower, perhaps moderately lower than the national rates.

We expect that Sofia differs from Bulgaria in a number of behavioral factors like alcohol consumption, smoking habits, diet, stress etc. Unfortunately there are only very limited data available about the distribution of those factors among Bulgarian population and they are not always comparable, because of different methodology used, age groups, lack of standardization etc. The data available are given in Table 1.14.

 

1.4.1 Need for Cardiovascular risk factor surveillance in Bulgaria

Bulgaria and other East European countries are undergoing major social, political and economic changes. The predominantly secluded society is fast moving towards a western lifestyle. We are now in the transition period. Like all facets of life, the health sector is also undergoing major changes. Bulgaria has one of the highest reported stroke mortality rates in the world.

Given the social and financial situation in the country, epidemiological studies will face resource limitations and logistic problems. The present financial constraints in Bulgaria cause difficulties in setting up surveillance programmes. Surveillance programmes are labor intensive (not such a major problem) but also needs a substantial financial input for equipment and biochemistry.

The cost of conducting surveillance must be compared with the cost of not doing it. The latter costs include reduced productive life due to disease that can be more readily prevented when the distribution of their causes in the population has been measured. In the absence of a sense of how health determinants are distributed in the population, substantial amounts of money can be spent on relatively inefficient preventive measures - e.g. drug treatment of hypertension.

 

1.4.2 Conclusions

1. Cardiovascular diseases have emerged as the major public health problem in Bulgaria. Primary prevention of risk factors seems to be the most powerful strategy to control this epidemic. The role of risk factor surveillance is paramount in this context. Prevention strategies will be most effective when based on valid estimates of the magnitude of the problem and the distribution of the risk factors in the community. A National Health Survey with special attention on CVD risk factors can give rise to data, which are essential for the planning and implementation of control programmes. Unless this is undertaken at the earliest it may be too late to control the epidemic.

2. Primary prevention i.e., preventing the disease-causing exposures, is in principle, the best strategy for controlling cardiovascular diseases. The well-known risk factors - smoking, raised blood pressure and hypercholesterolemia can be changed to a certain extend by dietary and life style modification based on research findings.

3. Limitations of a “high risk” strategy for the prevention of cardiovascular disease have been well demonstrated: For example many strokes occur in persons who do not meet the criteria for arterial hypertension. Even with active programmes to treat hypertension and other risk factors it is unlikely that the CVD epidemic will be controlled. There is some evidence that effective control requires shifting the whole population distribution in a favorable direction.

4. The World Bank’s development report for 1993 has provided policy guidelines for the rational utilization of resources. In the health sector it envisages the redistribution of financial outlay form tertiary care into prevention and primary care in the community. The bank has emphasized the need for re-orientation towards chronic disease prevention in Bulgaria. Bulgaria can import knowledge about how risk factors are related to disease, but cannot import information about the population distribution of risk factors in Bulgaria. Hence the importance of achieving a better understanding of the prevalence of known risk factors for CVD in Bulgaria.

Furthermore, there are features of the pattern of the cardiovascular mortality in Bulgaria - notably the very high mortality from stroke, which remain poorly explained. National surveillance data can provides the context for focused investigations into etiological questions requiring local answers.

 

1.5 The aims of the project

Against this background the aims of this project (and of the study to which it relates) are:

1. Measure the distribution of the principal cardiovascular risk factors in a representative sample of the Sofia population in a way that permits comparison with data published for representative samples in other countries (e.g. MONICA).

2. To explore associations between environmental exposures, behavioral factors and intermediate outcomes (such as blood pressure, blood cholesterol concentration etc.).

3. To assess the frequency with which particular combinations of risk factors are found and in which groups these combinations most commonly occur.

4. To make external comparisons - for example, with the MONICA data from other countries.

5. To consider implications for the further development of risk factor surveillance within Bulgaria in the light of both the methodological and substantive aspects.

6. To make a preliminary assessment of the relationships between risk factor distributions and the level of mortality attributed to IHD and stroke and to specify the most important etiological questions required from further local investigations.

7. To provide data, which can be used in the planning and monitoring of public health programmes directed towards Bulgarians’ most serious public health problem.

8. To identify more specifically those aspects of the cardiovascular disease profile in Sofia which remain poorly explained by the major risk factors and to identify questions that need to be investigated further in order to better understand why these diseases are so common in Bulgaria.

***

 


References: More information on Sofia Heart Study could be found in the collaborative site with Cambridge University,

http://www.phpc.cam.ac.uk/varna/stroke/Georgieva_Sofia_Heart_Study_Thesis.pdf

http://www.phpc.cam.ac.uk/varna/stroke/

 

 

Copyright © 2008 by the author.