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Copyright by Professor Omar Hasan Kasule Sr
MODULE OUTLINE
1.1 INTRODUCTION TO GENERAL EPIDEMIOLOGY
1.1.1 Definition, Scope, and Classification
1.1.2 Importance of Epidemiology:
1.1.3 Epidemiologic Methodology:
1.1.4 Historical Evolution of Epidemiologic Knowledge
1.1.5 Ethical Issues in Epidemiology
1.2 INTRODUCTION TO CLINICAL EPIDEMIOLOGY
1.2.1 Definitions, scope, and roles
1.2.2 Historical evolution of clinical medicine
1.2.3 Clinical epidemiology in diagnosis
1.2.4 Clinical epidemiology in treatment and prognosis
1.2.5 Clinical Trials on Humans
1.3 INTRODUCTION TO PUBLIC AND COMMUNITY HEALTH
1.3.1 Definition of Public Health
1.3.2 Disciplines That Assist Public Health
1.3.3 Public Health Programs and Strategies
1.3.4 History of Public Health
1.4 INTRODUCTION TO BIOSTATISTICS
1.4.1 Biostatistics as a discipline
1.4.2 History of biostatistics
1.4.3 Limitations of biostatistics
1.4.4 Career opportunities in biostatistics
1.5 INTRODUCTION TO COMPUTING
1.5.1 Information Revolution and Computer Age:
1.5.2 Information System
1.5.3 History of Computing
1.5.4 Computer Hardware Developments:
1.5.5 Computer Software:
UNIT 1.1
INTRODUCTION TO GENERAL EPIDEMIOLOGY
Learning Objectives
· Epidemiology: definition, scope, classification, and importance
· Strengths and weaknesses of the epidemiologic method
· Historical evolution of epidemiology
· Ethical issues in epidemiology
Key-words and terms
· Logic, deductive
· Logic, inductive
· Disease, determinants of disease
· Disease, distribution of disease
· Disease, mechanistic concept of disease
· Disease, non-mechanistic concept of disease
· Epidemiology, qualitative epidemiology
· Epidemiology, qualitative epidemiology
· Epidemiology, descriptive epidemiology
· Epidemiology, analytic epidemiology
· Study, observational study
· Study, experimental study
· Scientific method
· Hypothesis
· Empiricism
· Refutation
· Demographic transition
· Epidemiologic transition
· Hygiene
UNIT OUTLINE
1.1.1 DEFINITION, SCOPE, and CLASSIFICATION
A. Definition
B. Scope of Epidemiology:
C. Classification of Epidemiology
D. Sub-Disciplines of Epidemiology:
E. Supporting Disciplines.
1.1.2 IMPORTANCE OF EPIDEMIOLOGY:
A. Clinical Medicine
B. Public Health:
C. Risk and Actuarial Sciences
D. Epidemiology as a Profession
E. Famous Epidemiologists
1.1.3 EPIDEMIOLOGIC METHODOLOGY:
1.1.4 HISTORICAL EVOLUTION OF EPIDEMIOLOGIC KNOWLEDGE
A. 1st Epoch: Ancient Times to 1500 CE
B. 2nd Epoch: 1500-1750 CE
C. 3rd Epoch: 1750 - 1870 CE
D. 4th Epoch: 1870- 1945 CE
E. 5th Epoch: Period of Modern Epidemiology 1945 - Today
1.1.5 ETHICAL ISSUES IN EPIDEMIOLOGY
A. Ethical Approval
B. Informed Consent
C. Privacy and Confidentiality
D. Conflict Of Interest
E. Study Interpretation and Communication
1.1.1 DEFINITION, SCOPE, and CLASSIFICATION
A. DEFINITION
VARIOUS DEFINITIONS
The word epidemiology is derived from Greek. Epi = among, demo = people, and logos = study. Epidemiology is both a new and an old discipline. Its basic concepts and methodology have been known for centuries. It has however become an organized and recognized independent academic discipline in the past half-century. Epidemiology is both a methodology (for example study design) and substantive information (for example the epidemiology of coronary heart disease). The discipline of epidemiology can be defined in various ways, an indication of its wide scope in public health. It is a basic discipline of both clinical and preventive medicine. Being a methodological discipline it does not have a coherent specific subject matter. It is not a definable body of knowledge. It is a methodology of how to get knowledge. It studies health and disease in a community or a group of individuals rather than an individual. Epidemiological conclusions are based on comparison of groups. It is important to select the groups carefully to avoid bias.
STUDY OF THE DISTRIBUTION and DETERMINANTS OF DISEASE
Epidemiology is the study of the distribution and determinants of disease and injury frequency in human populations. Usually the actual study is carried out in a sample of a study population that is part of the target population. Mere count of disease events without relating them to the underlying population denominators leads to the logical error of the floating numerator. Epidemiologic study focuses on the population at risk. Epidemiologic study of disease distribution includes study of disease occurrence in terms of time, place and persons affected. The affected persons are described in terms of their age, sex, race, socio-economic status, occupation, and culture.
Epidemiologic study of disease determinants includes factors that cause or contribute to disease occurrence. Epidemiology also includes study of the natural history of disease (antecedents & consequences) with view to prevention. Also included is study of all phenomena that are related to disease causation and prevention. Epidemiology can be visualized as 2 types of triads. The first triad is a study of the agent, host, and environment of a disease. The second triad is study of the time, place, and persons involved in disease. The primary goals of epidemiology are prevention, control, and in rare instances eradicate disease and injury.
BASIC ISSUES
Epidemiology deals with the following basic issues about disease: definition, diagnosis, prognosis, measurement, transmission, determinants, natural history, treatment, prevention and control, as well as health care research.
POPULATION-BASED and CLINICAL EPIDEMIOLOGY
Population-based epidemiological study may give an accurate picture that cannot be obtained from study of individual patients in clinics because at the population level false-positive errors balance false negative errors leading to a more accurate result. Epidemiology like politics is the art of the possible. It does not provide conclusive proofs but provides enough information to allow taking preventive action. The purpose of both epidemiology and clinical medicine is to modify the natural history of disease. If left alone, disease will eventually lead to severe complications and death. The primary care physician deals with the causes of disease in the individual. The epidemiologist deals with causes of disease in the population. That is why epidemiology is also called population medicine. Classical epidemiology dealt with infectious disease. Its methodology was extended to chronic diseases over the past 50 years. The epidemiological methodology can be extended to study any event that has a time dimension. An event in this sense is looked at as a change of state.
RANDOM EVENTS
A central axiom of epidemiology is that disease is that disease is a random event in its occurrence but is not randomly distributed in the population. A distinction must be made between random and non-random events. Epidemiology studies random events and cannot be employed for non-random ones. Some man-made events are random because humans do not have a pre-conceived total plan or strategy with anticipation of the outcome. Smoking or driving very fast are man-made events that affect health. They are considered random and can be studied by the epidemiologist. Humans undertake or contribute to such events without prior knowledge or determination of the outcome. There are other man-made events that are not random. A good example is war that is prosecuted with a prior determination of objectives and knowledge of the outcome. Thus war casualties are a major distortion of the usual forces that interact in nature and cannot be studied as an epidemiological phenomenon.
STUDY OF CHANGE
Epidemiology studies phenomena of change that affect disease occurrence. Epidemiologic transition manifests as recurring cycles of epidemics or famines, receding pandemics, change in incidence of degenerative diseases and conditions related to the environment, or the emergence or re-emergence of infectious diseases. The causes of epidemiological transition are changes in the causes of disease, change of age distribution, and change of gender distribution. Demographic transition occurs when the age distribution of a community changes from a predominantly youthful population to one that has a predominance of the elderly with longer life expectancy. Demographic transition is a major factor in epidemiologic transition.
B. SCOPE OF EPIDEMIOLOGY:
FOUR INTER-LINKED STAGES
The scope of epidemiological study has widened and changed with time. It started as a study of epidemics. Then it became study of infectious disease. It was later extended to study of non-infectious diseases. It has now become a methodological discipline that is even beyond study of disease.
STUDY OF EPIDEMICS
Until the mid-19th century M, epidemiology was only a study of epidemics. Epidemics of infectious disease were frequent and epidemiologists were pre-occupied with them. We now know better and look at epidemics as excessive frequency of disease. The epidemic prevalence of a disease is markedly higher than the non-epidemic prevalence. Epidemics may be acute such as cholera or slow such as lung cancer or coronary heart disease. Thus it is still possible to define epidemiology as a study of epidemics if we consider chronic diseases like coronary heart disease and cancer as slow epidemics. Defining an epidemic requires knowledge of pre-epidemic pattern. It is also important to study the post-epidemic period to determine the end-point of the epidemic so that a decision can be made about stopping preventive intervention.
STUDY OF INFECTIOUS DISEASE STARTING CIRCA 1870
The last quarter of the 19th century witnessed many new discoveries in the microbiological disease etiology. The microbiological agents, their vectors, and modes of transmission were described. Disease patterns were studied and it was found that disease was not randomly distributed in the population and that there were factors determining the local patterns of distribution. Epidemiology in that era was closely related to microbiology. The book on infectious disease epidemiology is not yet closed. New agents of disease are being discovered. There is change in pathogenesis and transmission of known agents. Changes in human behavior lead to new patterns of disease transmission. New and recent discoveries are uncovering an infectious basis for chronic diseases that were considered non-infectious before.
STUDY OF NON-INFECTIOUS DISEASES STARTING CIRCA 1950 M
Studies in the period after the Second World War showed increasing incidence of chronic diseases due to an older population and relative decrease of infectious disease. Study of these diseases thus became a major pre-occupation of epidemiologists in Europe and America. They studied risk factors, the natural history, and preventive interventions. In this period use of the statistical methodology became more wide-spread. Epidemiology in this period was closely related to study of cancer which is the most serious of the non-communicable diseases. The term chronic is a misnomer because both infectious and non-infectious diseases can be chronic. It is better to talk about communicable and non-communicable diseases.
BEYOND HUMAN DISEASE, STARTING CIRCA 1980 M
Epidemiology has now become a purely methodological tool applied to several disciplines. In the field of health and disease it is applied to communicable and non-communicable diseases. It is used in the fields of health policy & management, health quality assurance, health planning and health evaluation. It is finding increasing application in the social and human sciences.
THE FUTURE OF EPIDEMIOLOGY
Epidemiology will have to contend with new challenges and frontiers: global warming, ozone depletion, environmental pollution, demographic changes, emerging infections, and re-emerging infections. Global warming will lead to increase of disease vectors because of higher ambient temperatures. It will also lead to the melting of the polar ice cap leading to rising sea levels will disrupt coastal ecosystems with yet unknown effects on health. It will affect the weather patterns and agricultural production. The depletion of the ozone layer will allow ultra violet radiation to reach the earth and cause damage to human, animal, and plant DNA. As countries develop industrially, their population structures change. They get more elderly dependent citizens and fewer young workers to support them. Rural to urban migration is creating megacities that have many social problems. New infectious diseases are appearing: HIV, Ebola, Hantavirus, and Lyme disease. Infectious diseases that had been defeated are re-emerging: dengue and tuberculosis. Drug resistance is increasing.
REDEFINITION OF EPIDEMIOLOGY
Epidemiology has expanded so much and has involved itself in so many fields of endeavor that it risks losing its original identity without at the same time picking up a new identity. This may result in its disappearance as a coherent discipline. As a scientific methodological discipline, epidemiology need not be confined to its public health origins. As a methodological discipline it can find applications in the clinical as well as health policy fields. The divorce of epidemiology from public health should be blamed on modern public health practitioners who have moved the field from the narrow confines of scientific investigations to social and policy issues that are more political than scientific. The pressure to be politically correct has also forced epidemiologists to present and interpret their evidence in ways that are considered appropriate. They have had to do this in order to have the audience of the public and the policy makers.
Another force pulling epidemiology from its scientific base lies in its very nature. Over the decades we have been able to decrease the risk of disease by preventive measures before we understood the causal chain in full. This was true of Snow’s work on cholera in London in the 19th century as it is true of falling lung caner rates due to decrease of smoking. The argument is that the epidemiologist should be more involved in the field with social and other interventions against disease rather than spend time doing careful but slow-yielding studies to understand causal mechanisms. However the involvement of the epidemiologist in social intervention may blind him to basic scientific research. For example some forms of intervention against disease may be acceptable to social stakeholders on economic, social, ethical, or other considerations. The epidemiologist may as a consequence be less inclined to purse research in that direction.
The possibility of dividing the discipline into basic epidemiology emphasizing causal research and applied epidemiology emphasizing intervention against disease in the field can be considered but would be difficult to realize in practice. Epidemiology is so inherently practical in its orientation that it would be difficult if not impossible to confine it to intramural pursuit of causal chains and mechanisms.
The emerging field of molecular epidemiology may resolve many of the dilemmas discussed above. Epidemiology can continue investigating causes of disease in the population using very accurate molecular techniques. It can also be involved in an effective way in disease prevention by using molecular techniques to characterize individual risk profiles so that interventions become more specific for each person.
The availability of a lot of data online is posing a new challenge to epidemiology. In the past epidemiologists used to spend a lot of time thinking about the research they intended to do and developing conceptual approaches and hypotheses before they started collecting data. Such serious thought was needed because data collection was not easy. With readily available data epidemiologists may hasten to analyses that will prove difficult to interpret because of inadequate conceptual thought and planning.
Exponential growth in the quantity and sophistication of statistical techniques also poses a novel challenge to traditional epidemiology. System analysis and meta-analysis are powerful tools that enable deeper understanding of phenomena but which may lead to loss of sight of the simplicity of epidemiology. Traditionally epidemiology never sought understanding all factors involved in disease causation in order to initiate prevention. It has always sought for one or two simple risk factors against which to intervene to break the causal chain. It has been a pride of epidemiologists that they can solve problems that they do not fully understand.
C. CLASSIFICATION OF EPIDEMIOLOGY
ON BASIS OF TYPE OF DATA:
Qualitative epidemiology describes the disease patterns as attributes without quantification. Quantitative epidemiology uses exact numerical data. There was relatively slow development of the epidemiological methodology when the discipline was qualitative. This changed rapidly when epidemiology became quantitative and started being treated as a serious science.
ON THE BASIS OF DATA SOURCE:
Epidemiological data can be obtained by observation of human phenomena (observational epidemiology) or by experimental intervention (experimental epidemiology). Observational epidemiology can be descriptive or analytic. Descriptive epidemiology describes the burden of disease and associated characteristics. It is the extension of demography into medicine. Analytic epidemiology studies causal relations between exposures and disease.
Experimental epidemiology involves intervention against a disease phenomenon and assessment of the effects of the intervention. It is in essence analytical.
ON THE BASIS OF APPLICATION:
We can talk of theoretical (basic) epidemiology and applied epidemiology. Those involved in theoretical epidemiology consider themselves the elite of the discipline who do not dirty their hands with data. They tend to work on the mathematical and philosophical aspects of the discipline which with time find application in the field. Epidemiological knowledge can be applied in various settings such as hospital epidemiology, clinical epidemiology, disease screening epidemiology, drug epidemiology, radiation epidemiology, genetic epidemiology, nutritional epidemiology, environmental epidemiology, occupational epidemiology, geriatric epidemiology, and public health epidemiology.
D. SUB-DISCIPLINES OF EPIDEMIOLOGY:
Epidemiological knowledge has grown so extensively in the past decade that specialization has become necessary thus giving rise to sub-disciplines of epidemiology. Theoretical epidemiology deals with the mathematical and statistical methodology used in data analysis and data interpretation. Descriptive epidemiology describes the patterns of disease occurrence in terms of place, time and person. Analytic epidemiology seeks to discover the underlying causes of diseases. Public-health epidemiology is a general term for the study of public health and preventive medicine which includes risk factors, outcome, treatment, and prevention of disease. Clinical epidemiology is concerned with the diagnosis and management of disease as well as assessing its prognosis. It can alternately be called clinical decision making. Hospital epidemiology deals with nosocomial infections and other aspects of hospital operations that can be studied using epidemiological methodology. Drug or pharmaco-epidemiology studies phenomena of adverse reactions and side-effects of drugs. Genetic epidemiology studies the patterns of inheritance of disease from the parents and how genetic and environmental factors interact in the final pathway of disease causation. Molecular epidemiology will revolutionize all our understanding of diseases, their causation, classification, and treatment. Occupational epidemiology studies diseases due to exposure to hazardous material or working conditions in the work-place. Environmental epidemiology studies the impact of air, water, and soil pollution on health.
E. SUPPORTING DISCIPLINES.
CLINICAL SCIENCES
The following disciplines assist in disease characterization: clinical medicine, pathology, and laboratory medicine. Clinical medicine involves description of symptoms and signs which taken together with diagnostic tests and response to treatment helps in case definition, a basic requirement in epidemiological studies.
DEMOGRAPHICAL SCIENCES
Demography is the study of the population in the aggregate and factors of change in the population. Demographic data provides the denominators needed to compute many epidemiological parameters such as rates, ratios, and proportions.
DATA and INFORMATION SCIENCES
Biostatistics and computer science are employed in data collection, management, and analysis. Developments in computer hardware and software have put enormous data handling and data analysis capabilities at the disposal of the epidemiologist.
BEHAVIORAL SCIENCES
Social and human sciences such as sociology, anthropology, demography, economics, and managerial sciences, help understand human behavior as it relates to disease occurrence and disease prevention.
ENVIRONMENTAL SCIENCES
Physical sciences such as physics, chemistry, geological, and atmospheric sciences provide data on causes of disease in the physical environment. <Read more…>