Introduction to Epidemiology PDF

Introduction to Epidemiology Edric D. Estrella, PhD, MPH, RPh Diploma in International Health Program Faculty of Management and Development Studies University of the Philippines Open University  Learning Objectives At the end of the session, the learner should be a...

Introduction to Epidemiology Edric D. Estrella, PhD, MPH, RPh Diploma in International Health Program Faculty of Management and Development Studies University of the Philippines Open University  Learning Objectives At the end of the session, the learner should be able to: define epidemiology and its branches, enumerate the objectives and uses of epidemiology, enumerate important historical developments in epidemiology, and enumerate the core epidemiologic functions. Definition of Epidemiology demos (common people) epi logos (on or upon) (study) Epidemiology  Definition of Epidemiology Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems. Last, 1988  Study a scientific discipline with sound methods of scientific inquiry at its foundation data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data  Study often described as the basic science of public health – quantitative discipline that relies on a working knowledge of probability, statistics, and sound research methods – a method of causal reasoning based on developing and testing hypotheses grounded in such scientific fields as biology, behavioral sciences, physics, and ergonomics to explain health-related behaviors, states, and events  Study Epidemiology is not just a research activity but an integral component of public health, providing the foundation for directing practical and appropriate public health action based on this science and causal reasoning.  Distribution Epidemiology is concerned with the frequency and pattern of health events in a population.  Frequency refers not only to the number of health events such as the number of cases of meningitis or diabetes in a population, but also to the relationship of that number to the size of the population The resulting rate allows epidemiologists to compare disease occurrence across different populations.  Pattern refers to the occurrence of health-related events by time, place, and person Person Place Time  Personal characteristics (Who) include demographic factors which may be related to risk of illness, injury, or disability such as age, sex, marital status, and socioeconomic status, as well as behaviors and environmental exposures  Place patterns (Where) include geographic variation, urban/rural differences, and location of work sites or schools  Time patterns (When) may be annual, seasonal, weekly, daily, hourly, weekday versus weekend, or any other breakdown of time that may influence disease or injury occurrence  Descriptive Epidemiology Characterizing health events by time, place, and person are activities of descriptive epidemiology. Who is getting the disease, where is it occurring, and how is it changing over time?  Determinants any factor, whether event, characteristic, or other definable entity, that brings about a change in a health condition or other defined characteristic  Determinants factors that bring about a change in a person’s health (both causal and preventive factors) – individual determinants: genetic makeup, gender, age, immunity level, diet, behaviors, existing diseases – environmental and societal determinants – encompass a wide range of natural, social, and economic events and conditions  Determinants Epidemiologists assume that illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual.  Analytic Epidemiology To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events.  Analytic Epidemiology Epidemiologists assess whether groups with different rates of disease differ in their demographic characteristics, genetic or immunologic make-up, behaviors, environmental exposures, or other so-called potential risk factors. Ideally, the findings provide sufficient evidence to direct prompt and effective public health control and prevention measures.  Health-related states or events Epidemiology was originally focused exclusively on epidemics of communicable diseases but was subsequently expanded to address endemic communicable diseases and non-communicable infectious diseases. By the middle of the 20th Century, additional epidemiologic methods had been developed and applied to chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health.  Health-related states or events Then epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise and seat belt use. Now, with the recent explosion in molecular methods, epidemiologists can make important strides in examining genetic markers of disease risk.  Health-related states or events Indeed, the term health-related states or events may be seen as anything that affects the well-being of a population. Nonetheless, many epidemiologists still use the term “disease” as shorthand for the wide range of health-related states and events that are studied.  Population group of people with a common characteristic (such as place of residence, gender, age or use of certain medical services) Patient – Clinical→ individual – Epidemiology → community  Application Epidemiology is not just “the study of” health in a population; it also involves applying the knowledge gained by the studies to community-based practice.  Application Epidemiologist uses the scientific methods of descriptive and analytic epidemiology as well as experience, epidemiologic judgment, and understanding of local conditions in “diagnosing” the health of a community and proposing appropriate, practical, and acceptable public health interventions to control and prevent disease in the community. Branches of Epidemiology Descriptive Analytical Epidemiology Epidemiology Who? How? When? Why? Where?  Objectives of Epidemiology 1. study the natural course of disease from onset to resolution, 2. determine the extent of disease in a population, 3. identify patterns and trends in disease occurrence, 4. identify the causes of disease, and 5. evaluate the effectiveness of measures that prevent and treat disease  Historical Development of Epidemiology Circa 400 B.C. – Hippocrates attempted to explain disease occurrence from a rational rather than a supernatural viewpoint. – He suggested that environmental and host factors such as behaviors might influence the development of disease. (On Airs, Waters, and Places)  Historical Development of Epidemiology 1662 (London) – John Graunt (haberdasher and councilman) published the Bills of Mortality → first to quantify patterns of birth, death, and disease occurrence, noting disparities between males and females, high infant mortality, urban/rural differences, and seasonal variations.  Historical Development of Epidemiology mid-1700s James Lind (ship surgeon) conducted one of the earliest experimental studies on the treatment of scurvy  Historical Development of Epidemiology 1800 – William Farr systematically collected and analyzed Britain’s mortality statistics. – He is considered the father of modern vital statistics and surveillance, as he developed many of the basic practices used today in vital statistics and disease classification. – He concentrated his efforts on collecting vital statistics, assembling and evaluating those data, and reporting to responsible health authorities and the general public.  Historical Development of Epidemiology 1847 – Ignaz Semmelweis discovered that the incidence of puerperal fever/childbed fever (common in mid-19th-century hospitals and often fatal)could be drastically cut by use of hand washing standards in obstetrical clinics – Vienna General Hospital's First Obstetrical Clinic - doctor wards had 3 times the mortality of midwife wards  Historical Development of Epidemiology 1854 – John Snow (anesthesiologist) conducted a series of investigations in London’s cholera outbreaks both to discover the cause of disease and to prevent its recurrence. – His work illustrated the classic sequence from descriptive epidemiology to hypothesis generation to hypothesis testing (analytic epidemiology) to application.  Historical Development of Epidemiology An epidemic of cholera erupted in the Golden Square of London. Historical Development of Epidemiology Historical Development of Epidemiology Historical Development of Epidemiology  Historical Development of Epidemiology In the mid- and late-1800s – Epidemiological methods began to be applied in the investigation of disease occurrence on acute infectious diseases. In the 1930s and 1940s – Epidemiologists extended their methods to noninfectious diseases and an explosion in the development of research methods and the theoretical underpinnings of epidemiology was seen post-WWII. – Epidemiology has been applied to the entire range of health-related outcomes, behaviors, and even knowledge and attitudes.  Historical Development of Epidemiology In 1947 Framingham Heart Study – 5,209 men and women (aged of 30-62) from the town of Framingham, Massachusetts, who had not yet developed overt symptoms of CVD or suffered a MI or CVA were carefully monitored to identify major CVD risk factors.  Historical Development of Epidemiology In 1950s – Richard Doll and Andrew Hill studied the relationship between tobacco use and lung cancer – 34,440 male British MDs surveyed about their smoking habits and followed for 20 years.  Historical Development of Epidemiology In the 1960s and early 1970s – Health workers applied epidemiologic methods to eradicate naturally occurring smallpox worldwide In the 1980s – Epidemiology was extended to the studies of injuries and violence.  Historical Development of Epidemiology In the 1990s, – The related fields of molecular and genetic epidemiology (expansion of epidemiology to look at specific pathways, molecules and genes that influence risk of developing disease) took root. – Infectious diseases continued to challenge epidemiologists as new infectious agents emerged (Ebola virus, Human Immunodeficiency virus (HIV)/ Acquired Immunodeficiency Syndrome (AIDS)), were identified (Legionella, Severe Acute Respiratory Syndrome (SARS)), or changed (drug-resistant Mycobacterium tuberculosis, Avian influenza).  Historical Development of Epidemiology In the 1990s and accelerating after the terrorist attacks of September 11, 2001 – Epidemiologists have had to consider not only natural transmission of infectious organisms but also deliberate spread through biologic warfare and bioterrorism. Today, public health workers throughout the world accept and use epidemiology regularly to characterize the health of their communities and to solve day-to-day problems, large and small.  Core Epidemiologic Functions public health field analytic surveillance investigation studies evaluation linkages