Epidemiology (1) Def basic concepts of in epidemiology
- 1. University of Port Harcourt College of Health Sciences Department of Preventive & Social Medicine EPIDEMIOLOGY (1): History, Definition and Basic concepts By Dr. Charles Tobin-West
- 2. Brief History of Epidemiology • Hippocrates (460 BC to 377 BC) is regarded as the father of medicine. He is also regarded as the pioneer of epidemiology because he showed great concern about the influence of environmental conditions on the occurrence and pattern of diseases. He made a lot of medical writings known as Hippocratic Collections or Corpus Hippocriticum in which he viewed disease as natural and not supernatural phenomenom. His best known contribution was his book titled “Airs” water and places. • Fracastorius, in de Contagione (1546) described transmission of infection by droplet, direct contact and contamination of clothing and utensils. • Guillanme de Baillou (1538 – 1616), French physician and founder of modern epidemiology. He studied variety of communicable diseases, epidemics and was probably the first to describe whopping cough in 1578. His greatest work in epidemiology was his compilation of a clear account of epidemics between 1570 and 1579, the first of such work after Hippocrates. He also defined rheumatism in its modern sense. His extensive description of plague, diphtheria, measles and other works. • John Graunt is often regarded as the founder of vital statistics, because he was the first to describe the use of numerical methods in the quantification and spread of diseases in his book the Natural and Political Observations on the Bills of Mortality (1662).
- 3. Thomas Sydenham (1624 – 1689). Was born in Dorset, England in 1624. He is recognized as a founder of clinical medicine and epidemiology. He has been called the British Hippocrates because he emphasised detailed observations of his patients and maintained accurate records. He made a detailed study of epidemics, which formed the basis of his book on fevers published in 1668. This book he further expanded into a standard text book, Observationes Medicae.He also popularised the use of quinine in the treatment of malaria. • James Lind (1716 – 1794). James Lind was a naval surgeon but made important epidemiological observations that led to the discovery that scurvy was as a result of vitamin C deficiency. He was the first to use lemon in the treatment of scurvy. • William Farr. In 1839 William Farr was a physician in-charge of statistics in England and Wales. He looked at the pattern of mortality and compared it with occupation. He was able to show that mortality rates differed with occupation, and so was related with one occupation. • John Snow was an anaesthesiologist, but during his time there was a lot of cholera outbreaks. In 1849, John Snow made a thorough investigation of cholera outbreaks by the use of spot maps and was able to map the sources of water supply in London from two water supply companies: South walk/Vauxhall and Lambert companies. He was able to show that cholera was caused by a water borne disease in his book “on the communication of cholera”, 37 years before vibro cholerae was discovered. Brief History of Epidemiology Cont.
- 4. Epidemiology Epidemiology: Epi - among Demos - People Logos - study Epidemiology means “studies among the people” Epidemiology is concerned with the study of factors that exert their influence upon the people, both negative and positive factors in contracting of diseases. Concept of epidemiology The central philosophy is that diseases do not occur randomly in a population. They follow a systematic pattern. A study of this systematic pattern can help us determine the aetiological factors responsible for the disease occurrence.
- 5. Definition of Epidemiology • Epidemiology is the study of the causes, distribution, determinants and deterrents of diseases or health related states or events in the human population and the application of this study to the control of health problems (John M. Last -1988, modified) • Characteristics of Distribution - Frequency (i.e. measurement and quantification of amount of disease present) - Pattern (who, where, when i.e persons, place, time) • Characteristics of Determinants- (Factors that increase or decrease the chance of contracting disease i.e. factors that determine susceptibility to disease : age, sex, race, parity, alcoholism, smoking, unprotected sex etc.) • Deterrents are factors that can hinder the progress of a disease of health related condition e.g. immunization and health education.
- 6. • Health –related states or events: These are conditions that influence health e.g. the use of tobacco, alcohol, use of seat belts, health seeking behaviour, immunological status, inapparent infection family size, residence, and occupation. • Human population – In this context human population is specific and it is the field of study of the epidemiologist, while the epizootiologist is concerned with the occurrence of disease in animals. • Control – is the major concern of public health. It is directed at limiting health effects or defects to the barest minimum influence or impact. Definition of Epidemiology Cont.
- 7. Scope of Epidemiology Scope of epidemiology includes: • The investigation of the causes and natural history of all types of diseases and medical conditions, irrespective of whether their frequencies show any epidemic fluctuations. Initially epidemiology was restricted to the study of epidemics of infection diseases. As these came under reasonable control in developed countries emphases shifted to chronic diseases of later life which are predominantly non-infectious or non-communicable e.g. HT, DM, RTA, CHD, malignancies. • Epidemiology is concerned with development and evaluation of preventive programmes; e.g. immunization and health education programme. – The assessment of treatments – e.g. clinical trials, community based studies – Planning of health services for specific and general population e.g. health services for oil workers, or prison inmates or a defined community e.g. Choba community. • Epidemiology goes beyond clinical medicine in the study of individual cases, to the study of groups of individuals or populations.
- 8. Uses of Epidemiology • To improve our understanding of disease and health. • Helps to clarify aetiological agents, factors in susceptibility, modes of transmission of infections agents, and environmental determinants of disease. • The design, conduct and interpretation of field trials for prophylactic or therapeutic agents such as vaccines or drugs etc. • Establishing the natural history of disease, disease profiles, time trends and projections into the future. • Used to monitor the health of a population or community, to chart the changes over time and between places, and to determine which factors are of major importance. By studying time trend it is possible to predict some future developments and device means of control. • Supplies many of the facts needed for heath planning. • Evaluation of the programmes of health agencies and departments. The tools used are incidence rates, specific rates, relative risk and attributable risk.
- 9. Aims of Epidemiology • To describe the extent or magnitude and the distribution of health and diseases problems in terms of persons place and time. • To identify aetiological or risk factors associated with disease causation. • To generate data necessary for planning, implementation and evaluation of health care services. In other to fulfill these aims, three different classes of epidemiological studies need to be carried out: 1. Descriptive studies 2. Analytic studies 3. Experimental studies. The ultimate aim of epidemiology is to lead to effective action: • To eliminate or reduce the health problem or its consequences. • To promote the health and wellbeing of society as a whole.
- 10. Epidemiology vs Clinical Medicine Variable Clinical Medicine Epidemiology 1 Unit of study Case or cases Defined population or population at risk 2. Concern Disease in the individual Disease in the entire population (both sick and healthy) 3. Diagnosis Makes diagnosis on individuals, derives prognosis, prescribes treatment Makes diagnosis from data (both existing or from studies). Seeks to identify particular source of infection, mode of spread, or aetiological factor in other to determine future trends and recommend control measures. 4. Evaluation Evaluates the progress of therapeutic intervention on the patient, makes adjustments if need be etc. Evaluates outcome of preventive and therapeutic measures instituted for effective management of public health programmes. 5. Direction of care Patient comes to the doctor to be assessed and treated. Epidemiologist goes to the community to find persons who have the disease in question or experience the suspected factor 6. Basis of concept Based on biomedical concepts with an ever increasing concern for refining the techniques for diagnoses and treatment at the individual level. The basis of epidemiology is “conceptual”, symbolised in tables, graphs and figures to to capture and expose the magnitude and trends of health care problems in the population.
- 11. 1. Finally, clinical medicine and epidemiology are not antagonistic. Both are closely related, co-existent and mutually helpful. 2. Most epidemiological enquiries could never be established without appropriate clinical considerations as to how the disease in question can be identified among individuals comprising the group under scrutiny. 3. Likewise, a knowledge of prevalence, aetiology and prognosis derived from epidemiological research is important to the clinician for diagnosis and management of patients and families.
- 12. Epidemiological Approach Epidemiological approach to health and disease is based on two major foundations: 1.Asking Questions 2.Making Comparisons Asking Questions: – What is the event? ( the problem) – What is the magnitude? – Where did it happen? – When did it happen? – Who are the affected? – Why did it happen? Related to Health Action – What can be done to reduce this problem and its consequences. – How can it be prevented in the future. – What actions should be taken by the community?. By the health services? By other sectors?. Where and for whom these activities be carried out? – What resources are required?. How are the activities to be organised? – What difficulties may arise, and how might they be overcome?
- 13. Making Comparisons: – The basic approach in epidemiology is to make comparisons and draw inferences. – This may be comparison of two or( more groups) – one group having the disease ( or exposed to risk factor) or comparison between individuals. – By making comparison, the epidemiologist tries to find out the crucial differences in the host environmental factors between those affected and those not affected. – In short, the epidemiologist weighs, balances and contrasts. Clues to aetiology comes from such comparisons. Epidemiological Approach Cont.
- 14. Conditions for Comparison • Ensure comparability between study and control groups. In other words both groups must be similar, so that ‘like can be compared to like’. • For facts to be comparable, they must be accurate, and they must be gathered in a uniform way. For example, the study and control groups should be similar with regard to age and sex compositions and similar other pertinent variables. • The best known method for ensuring comparability is randomization or random allocation. • Where randomization is not possible, ‘matching’ is done for selected characteristics that might confound the interpretation of results. • Another alternative is standardization which usually has a limited application to a few characteristics such as age, sex or parity. • For comparison to be appropriate, differences in terminology, definitions, classifications criteria and nomenclature must be standardized.