lEGTlll'ill'E'NllTlES EPIDEMIMUGY Second Edition
fllllllll RflSlIill Khan IUL Naravan
Published by 4 Sepoy Lines 10450 Penang, Malaysia Tel: +604 226 3459 Fax: +604 228 4285 Website: http://www.pmc.edu.my Designed and Layout by ACE DESIGN & PRINTING No.5, Jalan Putra 1, Taman Sri Putra, Kempas, 81200 Johor Bahru, Johor, Malaysia. Tel: +6016-608 4808 / +607-562 6264 Fax: +607-554 3144 E-mail:
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Perpustakaan Negara Malaysia
Abdul Rashid Khan Lecture Notes on Epidemiology / Abdul Rashid Khan, K. A. Narayan. ISBN 978-967-950-302-9 1. Epidemiology. I. Narayan,K.A II. Title. 614.4
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Foreword Epidemiology is the bread and butter of public health. It contributes the knowl edge of the what, where, when, why and how of diseases and its occurrence. Stu dents pursuing medicine must be equipped with the epidemiology knowledge and skills to be good medical and health practitioners. It will help strengthen the prac tice of evidence-based medicine and public health. Many books on epidemiology have been written for this purpose. However, to be more relevant for the local set ting, epidemiology books must include data and examples from the local medical and health scene. This is then the value of a local book on epidemiology, where lo cal data and examples brings relevance and meaningfulness for the local medical and health students. In Malaysia, local books in epidemiology are lacking. This book, ‘Lecture Notes on Epidemiology’ Second Edition is written by Professor Dr Abdul Rashid Khan and Professor K.A. Narayan, both of whom are experienced medical teach ers in community medicine. It is the improved and refined version of the first edi tion. The second edition maintains the qualities of an excellent text book for under graduate medical students in Malaysia. This book will help build a strong epidemi ology base for their future medical and health careers. This edition continues to provide local relevance and meaningfulness by incorporating local epidemiology data and scenarios. It covers many important areas of epidemiology and is written in a lecture note format making it simple for students to understand and follow. While the book is written mainly for undergraduate medical students, the book is also suited for teachers and practitioners of public health and for other under graduate students in the field of medical and health sciences. I am sure many stu dents in Malaysia will benefit from this book and will go on to become good medi cal and heath practitioners for the country. I must congratulate both the authors for making the second edition of this book possible and hope that their effort will en courage others to write such books in other fields of public health. ii
Professor Dr Zulkifli bin Ahmad, Department’of Community Medicine, School of Medical Sciences Deputy Dean (Research & Postgraduate studies), School of Dental Sciences Universiti Sains Malaysia, Kubang Kerian, Kelantan.
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Preface “Lecture Notes on Epidemiology” was originally written with the view of helping undergraduates have a basic knowledge of the subject. Since the book was pub lished in 2007, many students have given us valuable feedback. However, what was pleasantly surprising was when many colleagues, both academicians and health service personnel, informed us that they found the book helpful in their work. We had the choice of either reprinting the first edition or writing a second edi tion. We chose the latter, as based on the feedback received, we felt changes could be made to make the book better and more up to date. More examples, explana tions and newer data have been added. References to websites which give addi tional reading have been included. The main focus of the book, however, remains i.e keeping its relevance to Malaysia. We do not purport this to be a text book on epidemiology but rather an easy guide to improve the understanding of epidemiology. Much of the material of this book has been sourced from text books, journals and internet. We encourage the readers to refer to the source materials of this book which has been mentioned in the text, figures/tables, reference section and in the additional reading section. We fervently hope that this book will benefit the students as well as practicing doctors. Abdul Rashid Khan K.A. Narayan
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Acknowledgement We are indebted to Professor Amir S. Khir, the Dean and President of Penang Medical College, who agreed to publish the reprint as an e-book and to allow read ers to access it for free. We dedicate this book to our families; Dr. Azizah, Sarah Diyanah and Pushpa Narayan, for their patience and support. Finally, a note of thanks to all our col leagues and students for their invaluable suggestions and comments. Abdul Rashid Khan K.A. Narayan
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CHAPTER 1
Introduction to Epidemiology Man has always lived with disease and it has been his endeavour to conquer it. Medical knowledge has been derived to a great degree from intuitive and observa tional propositions and cumulative experiences gleaned from others. Health and disease can be studied in three basic ways, (i) observation of effects on individuals, (ii) laboratory experiments and (iii) measuring their distribution in population (epidemiology). The origin of the word epidemiology is from the Greek word “epi” meaning “upon”, “demos” meaning “people” and “logos” meaning “doctrine”, the literal translation would be “the doctrine of what is upon the people”. The International Epidemiological Association defines epidemiology as “the study of the distribution and determinants of health related states and events in the populations and the application of this study to the control of health problems”. The primary unit of concern is groups of persons not individuals.
HISTORICAL PERSPECTIVE Medicine has drawn richly from, firstly traditional cultures of which it is a part, later from biological and social sciences, and more recently from social and behavioural sciences. Medicine has now evolved into a social system heavily bu reaucratized and politicized. It is now more complex and the costs of health care are ever increasing.
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In ancient times, health and illness were interpreted in cosmological and anthro pological perspective. Medicine was dominated by magical and religious beliefs which were an integral part of ancient cultures and civilizations. Later the belief of disease causation shifted from spiritual to environmental factors. Hippocrates attempted to explain disease occurrence from a rational in stead of a supernatural viewpoint. He suggested that environmental and host fac tors such as behaviours might influence the development of disease. John Graunt (April 24, 1620 - April 18, 1674) is often regarded as the founder of vital statistics. He quantified patterns of disease, birth and death, noted male female disparities, high infant mortality, urban-rural differences and seasonal variations. Dr. John Snow, (15 March 1813 – 16 June 1858) a British physician and a leader in the adoption of anaesthesia and medical hygiene, is considered to be one of the fathers of epidemiology, because of his work in tracing the source of a cholera outbreak in Soho, England, in 1854, long before the organ ism was found by Robert Koch. Snow studied the epidemics of cholera in 1849 and hypothesized that the disease was caused by polluted drinking water, con trary to the ‘Miasma’ theory prevalent at the time. In 1854, Snow used a spot map to illustrate how cases of cholera were centred around the pump in Broadstreet. He also made a solid use of statistics to illustrate the connection between the quality of the source of water and cholera cases. He showed that com panies taking water from sewage-polluted sections of the Thames delivered wa ter to homes with an increased incidence of cholera. Snow’s study was a major event in the history of public health and can be regarded as the founding event of the science of epidemiology. In the 1800’s William Farr, (November 30, 1807 - April 14, 1883) considered as the father of modern vital statistics and surveillance, began to systematically collect and analyze Britain’s mortality statistics. His most important contribution was to set up a system for routinely recording the causes of death. Although he did not agree with Snow’s waterborne theory, he gave him a great deal of help in col lecting data to support it, in particular by providing the addresses of people who had died. 7
The more recent development of epidemiology can be illustrated by the work of Sir William Richard Shaboe Doll (28 October 1912 – 24 July 2005) a British physiologist who became the foremost epidemiologist of the 20th century, turning the subject into a rigorous science. He along with Sir Austin Bradford Hill (July 8, 1897 - April 18, 1991), English epidemiologist and statistician, studied the rela tionship between cigarette smoking and lung cancer. Studies such as these brought in the important concept of risk. Hill pioneered the randomized clinical trial. The Framingham Heart Study which started in 1948 saw the influence of “many exposures” such as smoking, obesity and elevated blood pressure on the outcome measure i.e. Coronary Heart Disease.
THE EPIDEMIOLOGICAL PERSPECTIVE Epidemiology is about information: the information needed for health plan ning, supervision and evaluation of the health-promotion and disease-control ac tivities. The key components of the data needed can be approached through a se ries of questions.
Mr. How returns from his epidemiological expedition with a new wife
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‣Who? – Who is affected? Referring to age, sex, social class, ethnic group, oc cupation, heredity and personal habits. (These are person factors). ‣Where? – Where did it happen? In relation to place of residence, geographi cal distribution and place of exposure (Place factors). ‣When? – When did it happen? In terms of months, seasons or years (Time fac tors). ‣What? – What is the disease or condition, its clinical manifestation and diag nosis? ‣How? – How did the disease occur? In relation to: the interplay of the spe cific agent, vector and source of infection, susceptible groups and other con tributing factors. ‣Why? – Why did it occur? In terms of the reasons for the disease outbreak. ‣What now? – The most important question - What action is now to be taken as a result of the information gained?
SCOPE OF EPIDEMIOLOGY Epidemiology covers all major health problems in the community including: ‣Communicable diseases ‣Chronic degenerative, metabolic, neoplastic diseases ‣Nutritional deficiencies ‣Occupational health and injuries ‣Mental and behavioural disorders ‣Population issues and demographic trends
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USES OF EPIDEMIOLOGY ‣The most important use of epidemiology is to increase the understanding of disease by looking at communities or populations. It is used to determine the health of a population by the design, conduct and interpretation of studies (See Community Diagnosis in Chapter 7). ‣Epidemiology is concerned with describing the natural history of disease, in cluding not only the clinical stages seen in hospitals and medical practice but inapparent, sub-clinical and carrier states and precursor states of chronic dis eases. ‣Epidemiology is used to monitor the health of populations (surveillance) to chart changes over time, place and person as well as determine which dis eases are of most public health importance. By analysing trends it is able to predict and devise methods of control. For example, in the 1900’s infectious diseases were common but these have been replaced by chronic diseases of long duration (See chapter “Patterns of disease”). ‣Epidemiology attempts to identify causative agents, the factors in the web of causation, the populations at highest risk, environmental and other determinants. For example, one can determine what are the contributory fac tors for lung cancer, eg. smoking, occupations etc, determine what is the risk of developing a disease in the presence of that factor (risk due to smoking) and what can be achieved by removing that risk (benefits of cessation of smoking). ‣It supplies information necessary for health planning and development, man agement of programmes of disease prevention and control and supplies tools for evaluating health programmes (Operations research). ‣It provides a foundation for public policy and for making regulatory deci sions especially those relating to environmental problems.
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THE EPIDEMIOLOGICAL RESPONSIBILITIES OF THE MEDICAL OFFICER The responsibility of the medical officer extends to the entire community and includes the healthy, the sick, those seeking help as well as those who do not and the unborn or dead. The clinician examines the patient and has to recognise and identify the pathog nomonic significance of the clinical signs and symptoms to reach a specific diag nosis and to prescribe the appropriate treatment. The epidemiologist looks at the population and has to select the diagnostic indicators most suitable for case defini tion of the diseases in that population; he must pre-select the methods and tests which can be applied for mass diagnosis. Neither approach is self-sufficient; they complement each other in the overall approach to solving health problems of the community.
SOME OF THE RESPONSIBILITIES OF AN EPIDEMIOLOGIST ARE: ‣Carry out public health administration. ‣Conduct disease surveillance for the area under his charge. ‣Investigate and bring about rapid control of disease outbreaks. ‣Plan and supervise specific health programmes for disease control. ‣Train health personnel in epidemiology and disease surveillance and control. ‣Conduct health surveys, operations research and programme evaluation. ‣Produce reports useful for decision-making in disease control and prevention. ‣Describe the natural history of a disease and identify its causes.
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ADDITIONAL READING http://www.ph.ucla.edu/epi/snow.html http://www.medscape.com/viewarticle/567457 Doll R, Hill AB (1950). “Smoking and carcinoma of the lung; preliminary re port”. BMJ ii (4682): 739–48. doi:10.1136/bmj.2.4682.739. PMID 14772469 Doll R, Hill AB (1954). “The mortality of doctors in relation to their smoking habits; a preliminary report”. BMJ i (4877): 1451–5. doi:10.1136/bmj.328.7455.1529. PMID 13160495
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CHAPTER 2
Dynamics of Health The widely acceptable definition of health is that given by the WHO in 1948 in the preamble to its constitution, which is as follows, “Health is a state of complete physical, mental and social wellbeing and not merely an absence of disease or in firmity”. However health is defined, it derives principally from forces other than medical care. Appropriate nutrition, adequate shelter, a non-threatening environ ment and prudent lifestyle contribute far more to health and well-being than does the medical care system. Health in any society should be defined in terms of prevailing ecological condi tions. Instead of setting universal health standards, each country should decide on its own norms for a given set of prevailing conditions and then look into ways to achieve that level.
PHILOSOPHY OF HEALTH ‣Health is a fundamental human right. ‣Health is the essence of productive life, and not the result of ever in creasing expenditure on medical care. ‣Health is inter-sectoral. ‣Health is an integral part of development. ‣Health is central to the concept of quality of life. ‣Health involves individual, state and international responsibility. ‣Health and its maintenance is a major social investment. ‣Health is a world-wide goal. 13
SPECTRUM OF HEALTH There is no clear-cut demarcation between health and disease. Health can range from optimum well-being to various levels of dysfunction. Health is dy namic, it is not static. There are levels of health as well as levels of sickness.
THE NATURAL HISTORY OF DISEASE It is the course of disease over time unaffected by treatment see (Figure 2.1)
Figure 2.1 Natural History of Disease and Levels of Prevention
1. STAGE OF SUSCEPTIBILITY
At this stage the disease has not developed but the groundwork has been laid by the presence of factors that favour its occurrence. Factors whose presence are
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associated with the increased probability of the disease developing later are called risk factors. Risk factors are immutable or susceptible to change. Neither will all individuals with risk factor necessarily develop the disease nor will the absence of risk factor ensure the absence of disease. Our inability to identify all the risk fac tors contributing to risk of disease limits our ability to predict its occurrence.
2. STAGE OF PRE-SYMPTOMATIC DISEASE
At this stage there is no manifestation of disease but, usually through the inter action of factors, pathogenic changes have started to occur.
3. STAGE OF CLINICAL DISEASE
By this stage sufficient end-organ changes have occurred so that there are rec ognisable signs or symptoms of disease. Depending on a specific disease, these are classified on morphological, functional or therapeutic considerations.
4. STAGE OF DISABILITY
There are a number of conditions which give rise to a residual defect of short or long duration, leaving the person disabled to a greater or a lesser extent.
PREVENTION Prevention is any activity which protects the individual or population from ex posure to the causes of disease, disability or injury, or which enhances the ability to withstand the onslaught of specific causative agents.
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Table 2.1: Levels of preventions and stages of diseases Adapted version of Leavell H.R and EG Clark, Preventive Medicine for the Doctor in His Community; 3rd Ed. New York, Mc Graw- Hill Book Company , 1965.
There are four levels of prevention and these are linked to the stage of the dis ease as shown in Table 2.1. Prevention and treatment is often viewed as mutually exclusive activities. How ever prevention is as much a part of clinical medicine as it is of public health. When we treat illness we are preventing death, complications and a multitude of effects on the patient’s family and the community. The spectrum of prevention should be viewed as integral to both public health and clinical medicine. Epidemi ology provides the tools for assessing a disease and the rational basis on which ef fective prevention programmes can be planned and implemented.
LEVELS OF PREVENTION 1. PRIMORDIAL PREVENTION
It is the prevention of the emergence or development of risk factors in coun tries or population groups in which they may have not yet appeared, i.e. to avoid the emergence and establishment of the social, economic and cultural patterns of living that are known to contribute to an elevated risk of disease, e.g. increase in salt and cholesterol intake, resulting in rise in prevalence of hypertension and con sequent development of a stroke. The main intervention is through individual and mass education. 16
2. PRIMARY PREVENTION
It is any action taken prior to the onset of disease which ensures that the dis ease will never occur. The actions are appropriate in stages of susceptibility. It is directed at altering susceptibility or reducing exposure of susceptible individuals.
(a) Health Promotion
It is the provision of conditions at home, school and work environment that fa vour healthy living, e.g. good nutrition, adequate clothing, shelter, rest and recrea tion and physical exercise. One activity is health education which includes topics ranging from instruction on hygiene to sex education, as applied to both infectious and non-infectious diseases. Figure 2.2 shows the health campaign themes in Ma laysia.
Figure 2.2 Health campaign themes of the Ministry of Health Malaysia. Source: Official website ofMOH
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(b) Specific Protective Measures
This form of primary prevention is targeted at specific diseases or type of in jury. Examples include immunizations, environmental sanitation and protection against accident and occupational hazards. Fluoridation of water supply and phar macological treatment of diseases to prevent subsequent end-organ damage (e.g. renal failure) or complications (e.g. stroke), are also example’s of specific protec tion. Table 2.2 shows the immunisation schedule for Malaysia – a specific protec tive measure. Malaysian Ministry of Health’s New Immunisation Chart Age in Months 3 5
Immunization BCG Hepatitis B DPT+Hib DPT/DT OPV
0 Dose1 Dose 1
1
2
Dose 2 Dose 1
Dose1
Dose 2
Dose2
Measles
6
12
18
Standard 1 No Scar*
B
DT
B
B
School Year Standard 6
Form 3
Dose 3 Dose 3
Dose3 Sabah #
MMR
Dose1
Additional Dose
Tetanus
B
Rubella
Dose 1
Table 2.2 Immunisation Schedule in Malaysia
3. SECONDARY PREVENTION
Secondary prevention are strategies that are applied in early disease, i.e. pre clinical and clinical stages. It is the early detection and treatment of disease. Sec ondary prevention interrupts the disease process before it becomes symptomatic, e.g. recognition and treatment of hypertension and transient ischemic attack for preventing a stroke.
EARLY DIAGNOSIS AND PROMPT TREATMENT
This is the main strategy of secondary prevention. Early diagnosis including screening and individual case finding and prompt treatment of the condition will 18
result in full restoration of function when the disease has only produced reversible body malfunction. For many infectious and non-infectious diseases the develop ment of screening tests have made it possible to detect latent and sub clinical dis ease in individuals considered at risk.
4. TERTIARY PREVENTION (a) DISABILITY LIMITATION
It is the prevention of complications of a disease before irreversible changes set in. These actions would limit disability, e.g. early mobilization or splinting for stroke patients to prevent contractures.
Figure 2.3 Splinting to prevent contractures in a patient suffering from stroke. Source: Effects ofSplinting on Wrist Contracture After StrokeA Randomised Controlled Trial Stroke. 2007;38:111-116
(b) REHABILITATION
It is appropriate in a stage of advanced disease or disability. It is the alleviation of disability resulting from disease and attempts to restore effective functioning (disease has already occurred and left residual damage; emphasis is on remaining abilities than losses). Modern rehabilitation includes psychosocial, vocational and medical components, e.g. a person who has suffered a stroke needs to be rehabili tated physically, mentally and socially to take part in daily social life and be a pro
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ductive member of the society. Figure 2.4 shows the services involved in manag ing a patient with stroke.
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PATIENT
Figure 2.4 Services involved in rehabilitating a stroke patient
HEALTH DEVELOPMENT Health development is defined as “the process of continuous progressive im provement of health status of a population”. Its product is, raising the level of hu man well-being, marked not only by reduction of illness but increase of positive physical and mental health related to satisfactory economic functioning and social integration.
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MEASURES OF HEALTH Indicators are required not only to measure the health status of a community, but also to compare the health status of one community or country with that of an other for assessment of health care needs, for allocation of scarce resources, and for monitoring and evaluation of health services, activities and programmes. Indicators help to measure the extent to which the objectives and targets of a programme are being attained. Indicators are often only an indication of a given situation or a reflection of that situation at a given time. If measured over time, they can indicate direction and speed of change and serve to compare different ar eas or groups of people at the same moment in time. As people continue to live longer, the goal of survival is to live as long as possi ble in good health and free of disease. However, positive health cannot be defined in measurable terms. Thus measurements of health have been framed in terms of illnesses (or lack of health), the consequences of ill health (morbidity, disability) and economic, occupational and domestic factors that promote ill health and all the antitheses.
A. MORTALITY INDICATORS
They are the most often used indicators of health. As infectious diseases are be ing brought under control, mortality rates are losing their sensitivity as health indi cators in developing countries, but they continue to be used as the starting point in health status evaluation.
1. Crude Death Rate It is defined as the number of deaths per 1000 population per year in a given community. It indicates the rate at which people are dying. Its usefulness is lim ited because of the influence of age-sex composition of the population. Crude death rate can be affected by disease, natural and man-made calamites. However, in the long term a decrease in death rate provides a good tool for assessing the overall health improvement in a population. 21
2. Expectation of Life It is the average number of years remaining at a given age. Life expectancy at birth is the average number of years that will be lived by those born alive into a population if the current age-specific mortality rates persist. Life expectancy at birth is highly influenced by a high infant mortality rate. Life expectancy at the age of one excludes the influence of infant mortality. Life expectancy at age of five excludes the influence of child mortality. It is estimated for both sexes separately.
Figure 2.5 Life expectancy in Malaysia and the World - 1975 - 2025 Source: http://earthtrends.wri.org: Population. Health. and Human Well-Being -Malaysia
An increase in the expectation of life is regarded as an improvement in health status. It is a good indicator of socio-economic development in general. As an indi cator of long- term survival, it can be considered as a positive health indicator. It has been adopted as a global health indicator. A minimum life expectancy at birth of 60 years was the goal for health for all by 2000 AD. Figure 2.5 shows the trend in life expectancy for Malaysia in comparison to the world.
3. Healthy Life Expectancy (HALE) Healthy life expectancy or health-adjusted life expectancy is based on life ex pectancy at birth but includes an adjustment for time spent in poor health. It is 22
most easily understood as the equivalent number of years in full health that a new born can expect to live based on current rates of ill-health and mortality. Healthy ageing is an important policy issue in the face of demographic challenges to the so cietal well-being and economic prosperity. If the population can remain healthy as they get older, they can also remain active, contributing to society and reducing strains on health and social systems. In Malaysia, a study by the Ministry of Health among the elderly found 81.4% suffered from at least one chronic medical illness and 12.7% had three or more chronic illnesses.
4. Infant Mortality Rate It is the ratio of deaths of children under one year of age in a given year to the total number of live births in the same year, usually expressed as the rate per 1000 live births. It is one of the most accepted indicators of health status not only for in fants, but also for the whole population, and the socioeconomic conditions under which they live. Infant mortality is an important component of under-5 child mortality. Not only does this indicator reflect health conditions, but also, and critically, it is a ro bust and sensitive measure of the social, economic and environmental conditions in which children (and others) live. One reason for this is that the post-neonatal contribution to infant mortality, i.e. deaths after the first 28 days of life, is almost entirely due to exogenous socioeconomic and environmental factors.
5. Child Mortality Rate It is defined as the number of deaths at 1 - 4 years in a given year per 1000 chil dren in that age group at the mid-point of the year concerned. It correlates with in adequate Maternal and Child Health services. It also relates to malnutrition, low coverage by immunisation and adverse environmental exposure and other exoge nous agents.
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6. Under-5 Mortality The under-5 mortality rate is the probability (expressed as a rate per 1000 live births) of a child dying before reaching its fifth birthday. As an indicator, it pro vides similar insights into a broad range of development factors, and has the added advantage in that it captures almost all mortality of children below age 5. The MDG (millennium development goals) targets are to “Reduce by two thirds the mortality rate among children under five”. Figure 6.2 shows the under-5 mortality rates for Malaysia from 1970 to 2002.
7. Under-5 Proportionate Mortality Rate It is the proportion of deaths occurring in the under-5 age group as a proportion of total deaths. This rate can be used to reflect both infant and child mortality rates. High rates reflect high birth rates, high child mortality rates and a shorter life expectancy.
8. Maternal (Puerperal) Mortality Ratio The maternal mortality ratio (MMR) is the number of women who die from any cause related to or aggravated by pregnancy or its management (excluding ac cidental or incidental causes) during pregnancy and childbirth or within 42 days of termination of pregnancy, irrespective of the duration of pregnancy, per 100,000 births. Such deaths are affected by various factors, especially general health status, nutrition, education, and all obstetrics services and care during pregnancy and childbirth. It accounts for the greatest proportion of deaths among women of reproductive age in most of the developing world. The MDG is to reduce by three quarters the maternal mortality ratio.
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9. Disease Specific Mortality Mortality can be computed for specific diseases. It is defined as the number of deaths from a stated cause in a year per average (mid-year) population. This rate gives an idea of the burden of the particular disease on the community.
10. Proportional Mortality Rate The simplest measure of estimating the burden of a disease in the community is proportional mortality rate. This measure tells us the relative importance of a specific cause of death in relation to all deaths in the population group. It is de fined as the number of deaths from a given cause in a specified time period di vided by the total deaths in the same period. However this rate has to be inter preted with caution as it fluctuates with place and time, and as the proportion for one disease becomes higher another will come down simultaneously.
B. MORBIDITY INDICATORS
They reveal the burden of ill health in the community. All of the following are the morbidity rates used for assessing ill health in a community:
1. Incidence and Prevalence These are the most important measures of disease frequency at a particular place and time. Incidence and prevalence give the burden of a given disease in a community and are used for comparison of diseases between places and at differ ent times.
2. Notification Rates For each country or state, certain diseases, usually those that have an impact on public health, need to be informed or notified to health authorities for action. The notification rates give the burden of the disease and help identify its trends.
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3. Hospital & Clinic Statistics This is a good source of information provided the data is stored and analysed. The disadvantage is that they do not relate to a defined population and vary with the services offered, e.g. a cardiovascular centre would have a high rate of cardio vascular diseases. The following are examples of hospital statistics: a) Attendance rates at out-patient departments, health centre’s, etc. b) Admission, readmission and discharge rates. c) Duration of stay in hospital. d) Spells of sickness or absence from work and school.
C. DISABILITY RATES
These are used to supplement morbidity and mortality rates.
1. Event Type Indicators Number of days of restricted activity Bed disability days Work loss (school loss days) within a specific period.
2. Person Type Indicators Limitation of mobility Limitation of activity.
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Figure 2.6 Global distribution of Disease in Disability Adjusted Life Years (DALYs) 2000 (000s) Source: WHO
Figure 2.7 Major burden of disease – leading 10 selected risk factors and leading 10 diseases and injuries, for low mortality developing countries. Source: http://www.who.int/whr/2002/whr2002_annex14_16.pdf
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3. DALY (Disability - Adjusted Life Year) The national burden of disease can be measured by DALY. The burden of dis ease is a measurement of the gap between current health status and an ideal situa tion where every one lives into old age, free of disease and disability. DALY is an indicator of the time lived with a disability and the time lost due to premature mor tality. DALY is the only quantitative indicator of burden of disease that reflects the total amount of healthy life lost to all causes whether from premature mortal ity or from some degree of disability during a period of time. (Figure 2.6, 2.7).
4. Years of Potential Life Lost It is a measure of the impact of premature mortality on a population; it is calcu lated as the sum of the differences between some predetermined end point and the ages of death for those who died before the end point. Two most commonly used end points are age 65 years and average life expectancy, e.g. 76.2 for females and 70.4 for males in Malaysia (2004).
D. NUTRITIONAL INDICATORS
These are often used to measure the health status of population groups (figure 2.8). As communities develop they often move from under nutrition to over nutri tion and their associated health problems. The common ones are: ‣Anthropometric measurements of pre-school children ‣Heights of children at school entry ‣Prevalence of low birth weight ‣Percentage of obese population ‣Per capita Calorie and Protein consumption
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Figure 2.8 Prevalence of Underweight children in 3 countries by year. Source: http://www.dcp2.org/pubs/PIH/6/Box/6.1 PIHFM.pdf
Table 2.3 Selected Health care delivery Indicators. Source: Ministry of Health health_facts_2006.pdf
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E. HEALTH CARE DELIVERY INDICATORS
These indicators show the availability and utilization of health services (table 2.3). They are useful for planning and allocation of resources. Often alternative systems of health care are also included in these statistics. The common ones are: ‣Doctor- population ratio ‣Doctor- nurse ratio ‣Population -bed ratio. ‣Population per health / sub-centre ‣Population per traditional birth attendant
Figure 2.9 Population per Doctor. Source: Department of statistics, Malaysia.
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F. UTILISATION RATES
It is expressed as the proportion of people in need of service who actually re ceive it in a given period, usually in a year. Health care utilisation is affected by factors of availability and accessibility of health services and the attitude of an in dividual towards his or her health and the health care system, e.g. proportion of in fants who are fully immunised, proportion of pregnant women who receive antena tal care, percentage of population using various methods of family planning, bed occupancy rate and bed turn-over rate.
G. INDICATORS OF SOCIAL AND MENTAL HEALTH
These cannot be measured directly; hence it is necessary to use indirect meas ures, i.e. indicators of social and mental pathology, which include suicide, homi cide, other acts of violence and crime, road traffic accidents, juvenile delinquency, alcohol and drug abuse, smoking, obesity, family violence, battered-baby and battered-wife syndrome, and neglected and abandoned youth in the neighbour hood. All these act as a guide for social action towards improving the health of the people.
H. ENVIRONMENTAL INDICATORS
They reflect the quality of the physical and biological environment in which diseases occur and in which people live. These are indicators relating to pollution of air and water, radiation, solid wastes, noise and toxic substances in food. The most useful indicators are those measuring the proportion of population having ac cess to safe drinking water and sanitation facilities.
I. SOCIO-ECONOMIC INDICATORS
The following developmental goals do not measure health directly but are very valuable for policy makers and planners as overall development influences health. ‣Rate of population increase
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‣Per capita GNP ‣Level of unemployment ‣Dependency ratio ‣Literacy rates (especially female literacy rates) ‣Family size ‣Housing - number of people per room ‣Per capita calorie availability
J. HEALTH POLICY INDICATORS
‣The proportion of GNP spent on health-related activities ‣Proportion of GNP spent on health services ‣Proportion of total health resources devoted to primary health care
K. QUALITY OF LIFE INDICATORS
Quality of life is difficult to define and even more difficult to measure. The physical quality of life index (PQLI) consolidates three indicators: infant mortal ity, life expectancy at age one and literacy.
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L. HUMAN DEVELOPMENT INDEX
(100.0)
Table 2.4 Malaysia’s human development index 2006 and underlying indicators in comparison with selected countries.
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Figure 2.10 Human development Index Malaysia 2000 – 2005 Source : Ministry of Finance and Ministry of Education, Malaysia
The Human Development Index (HDI) provides a composite measure of three dimensions of human development: living a long and healthy life (measured by life expectancy), being educated (measured by adult literacy and enrolment at the primary, secondary and tertiary level) and having a decent standard of living (measured by purchasing power parity, income). It provides a broadened prism for viewing human progress and the complex relationship between income and well being. The HDI for Malaysia was 0.823 in 2006, which gave the country a rank of 63rd out of 179 countries with data (Table 2.4 and Figure 2.10)
M. OTHER INDICATORS
These can be categorised as: Social Indicators : population, family formation, families and households, learning and educational services, earning activities, distribution of income, con sumption and accumulation, social security and welfare services, health services and nutrition, housing and environment, public order and safety, time use; leisure and culture, social stratification and mobility.
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Basic needs indicators: calorie consumption, access to water, life expectancy, deaths due to disease, literacy, doctors and nurses per population, rooms per per son, GNP per capita. Health for all indicators: heath policy indicators, social and economic indica tors related to health, indicators for the provision of health care, health status indi cators
SUMMARY BOX CHAPTER 2
• Health and disease are a continuum and two ends of the same spectrum. • Health interventions can be made at four levels, primordial, primary, secondary and tertiary. • Disease evolves over time, and as this occurs pathologic changes may become irreversible. • The aim is to push back the level of detection and intervention to the precursors and risk factors of disease thus emphasizing the role of prevention rather than curative medicine. Health and disease are multi- factorial. • The challenge for health professionals is to find out which factors are associative and which are causative. • The major burden of disease is hidden. The challenge is to detect it early and treat it promptly. Screening methods are the major tools employed.
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CHAPTER 3
Population Dynamics DEMOGRAPHY Demography is the scientific study of human population. It is concerned with growth, development and movement of human population and focuses its atten tion on three readily observable human phenomena, i.e. ‣Changes in population size (growth or decline) ‣Composition of the population ‣The distribution of population in space Knowledge of the interaction of demographic characteristics of a population and its health status is important for health service providers. Demography deals with five demographic processes namely: ‣Fertility ‣Mortality ‣Marriage ‣Migration ‣Social mobility These five processes are continually at work within a population determining size, composition and distribution.
FACTORS IN POPULATION DYNAMICS Three factors determine the population of any defined area: ‣Birth ( fertility)
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‣Deaths (mortality) ‣Migration The balance of these three factors determines whether a population decreases, remains stationary or increases in number. The relation between births and deaths is referred to as natural increase. When the net effect of migration is added to natural increase this is referred to as total in crease and is also called growth rate. The total population of Malaysia, according to the 2000 Census, was 23.27 million compared to 18.38 million in 1991, thus giving an average annual population growth rate of 2.6% over the 1991 - 2000 pe riod.
SOURCES OF VITAL AND HEALTH STATISTICS ‣Census: is conducted every 10 years. In Malaysia the fourth census was con ducted in June 2000 by the Department of Statistics. ‣Registration: of vital events, i.e. births, deaths and marriages are done by the National Registration Department in Malaysia. ‣Notification: of diseases (refer to chapter on communicable diseases). ‣Hospital and health facility records ‣Surveys: e.g. National Health Survey, 2nd national health and morbidity sur vey 1996, 3rd national health and morbidity survey 2006 The quality of information obtained from these various sources vary according to country or source, which often makes comparison difficult. Common problems include: ✴Absence of a uniform and standard method of collection. ✴Lack of completeness with respect to data record and extent of coverage. ✴Inaccuracy in recording cause of death and age.
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✴Reporting agencies, especially in rural areas, being persons who are not aware of the relevance and importance of registration. ✴Concealment, under notification, and inaccurate diagnosis of notifiable dis eases.
DEMOGRAPHIC CYCLE This is the term used to describe the demographic trends of a given country, and it passes through five stages depending on the birth and death rates. These are greatly influenced by socio economic factors. The stages are: 1. HIGH STAGE (HIGH STATIONARY)
This stage is characterised by a high birth rate and a high death rate which can cel each other and the population remains stationary.
2. SECOND STAGE (EARLY EXPANDING)
The death rate begins to decline, while the birth rate remains unchanged. Many countries in South-East Asia and Africa are in this phase. Death rates decrease rap idly as a result of improved health conditions and sanitation.
3. THIRD STAGE (LATE EXPANDING)
The death rate declines still further and the birth rate tends to fall. The popula tion continues to grow because births exceed deaths.
4. FOURTH STAGE ( LOW STATIONARY)
This stage is characterised by low birth and low death rate with the result that the population becomes stationary. Zero population growth has already been re corded in many industrialised countries.
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5. FIFTH STAGE (DECLINING)
The population begins to decline because birth rate is lower than the death rate. In the 1970s, Malaysia had relatively high birth and death rates. By 1990, Ma laysia experienced a more rapid decline in birth and death rates. The proportion of the young population continued to decline while the older age group increased. This trend continued into the current decade and now Malaysia is considered to be in the third stage of demographic transition.
WORLD POPULATION TRENDS Nearly 2000 years ago, world population was estimated to be around 250 mil lion. In the year 1800 the world population reached one billion, the second billion came around 1930, the third billion came around 1960, the fourth billion in 1974, the fifth billion in 1987, and sixth billion in 1999. The global population trends show a paradox, on the one hand in many devel oping countries fertility is declining rapidly and there are low fertility rates in de veloped countries, but on the other hand there is a massive increase in world popu lation. In the “World Population Assessment and Projection The 1996 edition”, the United Nations Population Division projects a global population of 8.04 billion for the year 2025 and 9.37 billion for 2050. According to this medium variant, an increase of some 2.35 billion people can be expected worldwide between 1995 and 2025; and an additional 1.3 billion between 2025 and 2050. In 1998 about three fourths of the world’s population was living in the develop ing countries. The most populous region in the world was the Western Pacific re gion with about 28% of the world’s population; about 25% inhabited South-East Asia region. India, Indonesia and Bangladesh are among the most populous coun tries in the world and account for 88% of the region’s population.
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POPULATION TREND IN MALAYSIA - SIZE AND GROWTH Malaysia’s population more than doubled between 1970 and 2000, rising from 10.4 million in 1970 to reach 23.2 million in 2000. When non-citizens, mainly con sisting of migrant labour, is included, the figure was about 23.5 million. On an av erage the growth rate has declined from decade to decade, but became apparent only in the 1990s. Almost 80% of the population is located in Peninsular Malaysia and just under 10% each in Sabah and Sarawak. In Peninsular Malaysia the states show varying growth rates. These are greatly influenced by immigration. Sabah has shown the fastest growth due to high fertility levels and very high levels of im migration.
POPULATION STRUCTURE There are two broad uses of the knowledge about the population composition and structure. ( Figure 3.1) It provides evidence of past events in the history of populations. Ecological processes that human populations have gone through may leave marks on the structure of populations.
Figure 3.1 Population Pyramid Malaysia Source: Department of Statistics, Malaysia http:// www.statistics.gov.my
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It allows the assessment of the limits of organisational development in a par ticular population.
Figure 3.2 Population, Health, and human well-being-malaysia 1975-2025 Source: http://www.earthtrends.wri.org
In the 1970s, Malaysia had a typical age pyramid with a high percentage of young children. By 1990, due to a rapid decline in birth and death rates, the pro portion of the young population began to decline while the older age group in creased. This trend has continued up to the present. Figure 3.2 shows the pro jected change in the proportion of the population from 1975 to 2025.
DEMOGRAPHIC MEASURES DEPENDENCY RATIO
This measures the proportion of those economically productive to those who are dependent: 41
A high dependency ratio is a reflection of great strain on the productive mem bers of the population to provide for non-productive members. Population aged = 28 in the of age year upto 1 year PNMR
=
x 1000
days year of live Death Number in a year of births children in the
