Lecture 1 Definition and uses of Epidemiology PDF

Definition and Uses of Epidemiology Dr. Iman Wahdan Professor of Epidemiology High Institute of Public Health Alexandria University  Definition and uses of Epidemiology The word Epidemiology originates from the Greek words epi...

Definition and Uses of Epidemiology Dr. Iman Wahdan Professor of Epidemiology High Institute of Public Health Alexandria University  Definition and uses of Epidemiology The word Epidemiology originates from the Greek words epi (upon), demos (people) and logy (study of). Epidemiology is "the study of the distribution and determinants of health-related states in specified populations, and the application of this study to control health problems”. Components of the definition:  Study: Epidemiology is the basic science of public health. It is based on principles of statistics and research methodologies.  Distribution: Epidemiologists study the distribution of frequencies and patterns of health events within groups in a population. To do this, they use descriptive epidemiology, which characterizes health events in terms of person, place and time.  Determinants: Epidemiologists also attempt to search for causes or factors (biological, physical, social) that are associated with increased risk or probability of disease. This type of epidemiology, where we move from questions of "who," "what," "where," and "when" and start trying to answer "how" and "why," is referred to as analytical epidemiology.  Health-related states: Epidemiology is applied to the whole spectrum of health- related events, which includes chronic disease, environmental problems, behavioral problems, and injuries in addition to infectious disease.  Populations: One of the most important distinguishing characteristics of epidemiology is that it deals with groups of people rather than with individual patients (population medicine).  Control: Epidemiology has an active role. Epidemiological data steers public health decision making and aids in developing and evaluating interventions to control and prevent health problems. This is the primary function of applied or field epidemiology. Epidemiology is an interdisciplinary field that draws from biostatistics, social and behavioral science, toxicology, pathology, virology and microbiology, genetics and clinical medicine. 2  Uses of Epidemiology There are seven uses of Epidemiology: 1. Study the history of health of populations 2. Diagnose the health of the community 3. Study the functioning of health services 4. Estimate the individual risks 5. Complete the clinical picture of diseases 6. Identify syndromes 7. Search for causes 1. Study the history of health of populations and the rise and fall of diseases in the population. Useful ‘projections' into the future may also be possible. It is also necessary to investigate changes in various factors affecting health and in causes of death. Changes in factors affecting health: - Recent increase in the number of motor vehicles - The change in food and feeding habits - More smoking among women - More women going to work - Less physical activities - Exposure to multiple chemicals and physical agents - Increased use of medicines - Increasing trends of crimes - Increasing use of television, hundreds of channels - Increasing use of computers 3 Changes in causes of death: The leading causes of death have shown marked changes. The reasons of changes could be:  Variations in diagnosis or reporting e.g. new methods of diagnosis.  Changes in the fatal course of the disease due to modern methods of early diagnosis and discovery of effective drugs.  Aging of the general population as a result of reduced impact of infectious diseases and improved medical care. 2. Diagnose the health of the community which can provide a key to: - Types of problems that require attention. - Need for specific health services. 3. Study the functioning of health services: - How they are working, - Whether the community needs are covered, - If the services are utilized. 4. Estimate the individual risks of acquiring diseases: Epidemiology is useful to estimate the risks of suffering from a disease, an accident or a defect and the chances of avoiding them. 5. Complete the clinical picture of diseases: It is important to find all kinds of patients whether symptomatic (clinical cases) or symptomless (subclinical cases). Early detection of subclinical cases may offer opportunities for prevention. 4 6. Identify syndromes: A syndrome is a group of signs and symptoms that occur together and characterize a particular abnormality. It could be identified by describing the distribution and associated phenomena in the population. There are several examples of syndromes connecting many diseases together e.g. AIDS and Down syndrome. 7. Search for causes: The main use of Epidemiology is to discover causes of health and disease so as to increase understanding and help improve the people's health. Finding causes is easy in acute infectious diseases and difficult in chronic diseases which are usually a product of interaction between host and environment. Important definitions in Epidemiology Health: It is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity. Public Health: Field of medicine and hygiene dealing with the prevention of disease and the promotion of health. Disease: Deviation from normal health. Sporadic cases: Occasionally occurring cases. 5 Endemic: The constant presence of a disease or infectious agent within a certain population at a given geographic area. Epidemic: The occurrence in a community or region of cases of an illness clearly in excess of normal expectancy for the area, the specific population and the season of the year. Pandemic: Worldwide epidemic. Outbreak: Localized epidemic. Contamination: The presence of an infectious agent on a body surface or on or within articles or substances including water, milk or food. Pollution: The presence of offensive, but not necessarily infective matter, in the environment. Infection: Entry, development or and multiplication of an infectious agent in the body of man or animal, not necessarily resulting in overt disease or apparent illness. Infectious disease: A disease of man or animals resulting from an infection with a pathogen. 6 Communicable disease: An illness due to a specific infectious agent or its toxic products which arises through direct or indirect transmission of that agent from a reservoir to a susceptible host. Incubation period: The time interval between exposure to an infectious agent and the appearance of the first sign and symptom of the disease in question. Period of communicability: Time during which the causative agent may be transmitted directly or indirectly from a reservoir to a susceptible host. Non communicable disease: A miscellaneous group of health related conditions that are not communicated through infective pathogens and may cause impairment, disability, handicap or even premature death i.e. a disease that is not infectious or contagious e.g. hypertension, cancer, diabetes, asthma, allergy and cardiovascular diseases. Such diseases may result from genetic or lifestyle factors. Risk factor: An aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or inherited characteristic that, on the basis of scientific evidence, is known to be associated with meaningful health related conditions. It is an attribute or exposure that is associated with an increased probability of a specified outcome, such as the occurrence of disease Risk factors may be: - non modifiable such as age, gender, race, family history and genetic factors - modifiable such as smoking, alcohol, nutrition and exercise. 7 Latent period: A delay between exposure to a disease causing agent and the appearance of manifestations of disease e.g. exposure to ionizing radiation and appearance of leukemia. Chemoprophylaxis: The administration of a chemical, including antibiotics to prevent the development of an infection to active manifest disease. Chemotherapy: The use of a chemical, including anti-cancer drugs to cure a clinically recognizable disease or to limit its further progress. 8