What is Epidemiology Part 1

Chapter 1 1. What is epidemiology? The word “epidemiology” comes from three Greek words: Epi= “on, upon, or befalls” Demo = “people or populus” Logos = “study or count” So, epidemiology can be defined as the study of the people’s health. 2. Epidemiology seeks to answer →What is the status of the population’s health? →What are the causes of disease? →What interventions can prevent disease and improve wellbeing? 3. Definition of Epidemiology The study of the distribution and determinants of health-related states or events in the population • Some groups of people are affected more than others → How frequent is the health condition? → Among whom? → Where? → When? 4. Determinant: any factor that brings about change in a health condition or other defined characteristic: Bacteria, Diet, Exercise, Medications, Ergonomics, Environmental factors, Socioeconomic factors 5. The study of the distribution and determinants of health-related states or events in the population  Disease  Death  Injury  Disability  Behaviors 6. The study of the distribution and determinants of health-related states or events in the population, and the application of this study to protect and promote public health.  Application: Using epidemiologic information to make recommendations about interventions to: →Prevent disease →Cure disease →Improve wellbeing 7. Scientific Method & Observation: a. Epidemiology uses scientific research methods similar to basic sciences b. Epidemiology is an observational science that capitalizes upon naturally occurring situations 8. Natural Experiments: Naturally occurring circumstances in which groups of people have different levels of exposure to a factor causal in a way that is similar to an actual experiment 9. Epidemiology and Medicine: a. Epidemiology:  Concerned with populations.  Uses information to make associations between exposures and diseases.  Confirms findings (associations) using analytical studies.  Recommends community intervention to prevent health problem. b. Medicine:  Concerned with individuals.  Uses information to make a diagnosis.  Confirms findings (diagnosis) by conducting additional diagnostic tests.  Recommends a prescribed medical treatment to treat health problem 10. Key Terms in Epidemiology A. Epidemic:  “The occurrence in a community or region of cases of an illness, specific health-related behavior, or other health related events clearly in excess of normal expectancy.” B. Endemic:  “An expected, constant level of disease in a population.”  Annual occurrence, normal expectancy, and epidemic frequency of a hypothetical disease C. Pandemic:  “An epidemic occurring worldwide, or over a very wide area, crossing international boundaries, and usually affecting a large number of people.” 11. Terminology  Communicable: Infectious (transmissible) from person-to-person.  Non-communicable (NCD) Non-infectious. Sometimes known as chronic  Morbidity: Illness, injury or disability  Mortality: Death 12. History of Epidemiology:  Classical antiquity (before 500 a.d.): Thought that disease was caused by supernatural forces  Renaissance (1200-1699): Disease can be prevented. In Italy, “purification” and isolation were used by governments to protect wealthy citizens.  Quantitative reasoning o Made possible by… o Routine collection of population-based data (e.g., vital statistics system) o Mathematical tools to calculate chance & probabilities  Comparative Studies: “The effect of any potentially beneficial treatment, or of any toxic substance, can only be assessed by a comparison of closely similar subjects receiving and not receiving it.” (Alexandro Louis) 13. John Snow (1813-1858) o o o o o Considered the father of epidemiology because he pioneered methods of collecting and analyzing population-based data Considered the father of epidemiology because he pioneered methods of collecting and analyzing population-based data English physician, anesthesiologist Innovated key epidemiologic methods still in use today Believed cholera was transmitted by contaminated water & was able to demonstrate this association Snow’s “Natural Experiment”  Two different water companies supplied water from the Thames River to this area.  In 1852, the Lambeth Company relocated its sources of water to a less polluted portion of the river.  In 1854, another outbreak occurred. Snow noted that residents served by the Lambeth Company had fewer cases of cholera than those served by the Southwark & Vauxhall Company. John Snow’s Contributions   Powers of observation and written expression Application of epidemiologic methods Role of epidemiologic studies in public health   Sanitary Reform Movement Bacteria discovered (1870) and linked with disease Disease now defined by lab-based diagnoses rather than patient complaint Increased effectiveness of public health action (e.g., control of cholera, typhoid fever, tuberculosis) 14. Alexander Fleming (1881-1955) discovered the antimicrobial properties of the mold Penicillium notatum  The antibiotic became available toward the end of World War II.  “Office of Malaria Control in War Areas” established in 1942  Became “Centers for Disease Control” in 1946- 1950s – Today 15. Noteworthy Epidemiologic Findings  Sanitation and hygiene  Vaccination  Antibiotics  CHD risk factors  Smoking & lung cancer  Growth in understanding of social determinants of health 16. Epidemiology past & present: New ways of thinking about disease, and new diseases & events, have motived epidemiologic innovation   1. Five majors of using epidemiology: Historical, Community health, Health services, Risk assessment, Disease causality 2. Historical: Study history of health of populations E.g., Decline in infectious disease mortality a. Epidemiology transition: A shift in patterns of morbidity and mortality from determinants related primarily to infectious and communicable diseases to determinants associated with chronic, degenerative diseases. b. Demographic transition: The epidemiologic transition– a shift in patterns of morbidity and mortality from communicable diseases to non- communicable diseases Coincides with The demographic transition– a shift from high birth & death rates (found in agrarian societies) to much lower birth & death rates (found in developed countries) 3. Community health use a. Diagnose health of community     Health Services Use: Study the working of health services Examples: Operations research, Disease management Risk assessment use: Estimate individuals’ risks of health conditions Risk: probability an event will occur Risk factors and risk assessment: Risk factor: an exposure associated with an adverse health outcome. Risk assessment: a method used to provide quantitative measurements of risk. What is the exposure? What is the chance I will be exposed? If I’m exposed, what is the chance I will become ill? Search for the causes of health & disease (analyticalepidemiology) What exposures are associated with outcome X? What are the determinants of diseaseY? Genetic factors? Behavioral factors? Physical environment? Social environment? Natural History of use Distal and Proximal Determinants Outcomes: Gun-related homicides and asthma Proximal (“Near”) Determinants: Access to guns, Gang affiliation Air quality in neighborhood, Time spent outside Distal “far” Determinants: Gun laws, Social norms, Law regulating, air pollutants and enforcement of these laws 4. Three types of prevention From a public health standpoint, there are three types of prevention: A. Primary: before disease occurs (prevent exposure) B. Secondary: during progression of disease (prevent symptoms) C. Tertiary: during later stages of disease (minimize severity) 5. Relationship between natural history of disease, levels of prevention, and distal vs. proximal determinants Stage 1: Pre-disease -> Primary prevention -> Focus on distal determinants Stage 2: Underlying disease -> Secondary prevention -> Focus on proximal & distal determinants Stage 3: Apparent disease -> Tertiary prevention -> Focus on proximal determinants Example: 1. Focus on distal determinants: Prevent sun exposure (sunscreen, shade) 2. Focus on proximal & distal determinants: Prevent symptoms (screen & remove suspicious moles) 3. Focus on proximal determinants: Minimize severity (treatment) Conclusion:  Epidemiologists study distribution and determinants of health- related states and events in populations to improve public health.  Uses of epidemiology include historical, community health, health services, risk assessment, and disease causality research.  Natural history of disease is related to proximal and distal determinant and levels of prevention 12. Research question in Epidemiology: Descriptive epidemiology is concerned with the amount and distribution of health conditions within a population. (How many? Who? Where? When?) Analytic epidemiology examines associations between exposures and health conditions. (Why? How?) 13. Descriptive Epidemiology A. Describes patterns of disease or health- related exposures by  Person variables (sex, age, race, income etc.)  Place variables (neighborhood, state, country, etc.)  Time variables (e.g. 1980 compared to 2020?  Asks: “Who, where, and when does disease occur? B. Disease and health factors are not uniformly distributed in the population and in time. C. Descriptive epidemiology helps us identify who disease or health factor most effects, where it is most common, and when it is most problematic. D. A descriptive epidemiology research question, therefore, takes the form: How does (disease distribution), (health factor) differ by (person: age, sex…) (place: state, country…) (time: decade, year)? 14. Analytical question: A. Seeks to identify causes of disease or health, examining how disease occurrence relates to particular exposures Asks: “Does X cause Y?” B. When epidemiologists ask an analytic epidemiology question, it is usually of the format: Does (exposure) cause (outcome)? C. Exposure vs outcome  Exposure: Refers to a factor we think may cause an outcome that we are studying. Could be an environmental agent, a personal characteristic or a behavioral factor.  Outcome: Refers to a factor that we think may be a consequence of the exposure that we are studying. Could be any kind of medical or social problem D. Note: outcomes can also be positive, e.g., recovery or full-term birth Part 1 TYPES & SOURCES OF EPIDEMIOLOGIC DATA What is “epidemiologic” data? o Population-based data containing information about health Qualitative vs. Quantitative Data o Qualitative- uses words Quantitative- uses numbers Primary and Secondary Data Primary o You collect data for analysis Secondary o Someone else collected data Most common Drawback: lack of control over how data were collected Types of Descriptive Epidemiologic Data o Vital statistics: Births, deaths, marriages, divorces o Surveillance data: Incidence and prevalence of health-related states and events by person, place, and time variables o Registry data: Aggregated (compiled) databases about specific health-related states or events Vial statistics: From vital records: o Birth certificates o Death certificates o Marriage & divorce certificates o Surveillance Data: Surveillance data are collected by “surveillance systems,” which monitor the distribution of health- related states or events by person, place, and time Communicable & emerging diseases o NCD/Chronic diseases o Other health events (pregnancy, injury, etc.) Steps in a disease surveillance system o Step 1: Occurrence of health event in the individual(s) o Step 2: Health event recognized by reporting source (hospital, healthcare provider, etc.) o Step 3: Health event reported to responsible public health agency (local, state, federal) o Step 4: Control and prevention activities Notifiable/Reportable Diseases Some communicable diseases are “notifiable” (aka “reportable”) Reporting is mandatory by law List of Notifiable Diseases Registry Data: A registry is an organized system for the collection, storage, retrieval, analysis, and dissemination of information on individual persons who have: o A particular disease, or A risk factor that predisposes them to the occurrence of a health condition, or o Prior exposure to substances or circumstances known or suspected to cause adverse health events Characteristics of registries o Focus on a particular disease or exposure o Collect and link data from multiple sources (e.g., various types of medical records, vital statistics) Ascertain cases by combing through likely sources (e.g., examining hospital discharge records for evidence of birth defects) o Conduct follow-up investigations on enrolled person Examples of Registry Data and Usage o Registries of blind persons used to determine extent of blindness within a population due to preventable or treatable conditions o Brain cancer registries used to investigate suspected cancer clusters o Bone marrow donor registries keep data on individuals who are willing to donate bone marrow o Exposure registries keep data on persons living near toxic waste sites who may be exposed to substances with Part Two: INTRODUCTION TO EPI MEASURES General information: o In epidemiology, quantitative measures of frequency are used to describe the occurrence of disease, morbidity, mortality, and other health issues in populations. o Prevalence o The proportion of existing cases of a disease or health condition, or deaths in a population at some designated time. o “Burden” of disease o Prevalence Primarily used to describe chronic conditions (e.g. HIV infection, diabetes) or risk factors/behaviors (e.g. cigarette smoking, bike helmet use, etc.)  The most helpful measures for determining health spending and service provision  Generally measured in surveys or cross- sectional studies 1. Incidence  Refers to the occurrence of new disease or mortality within a defined period of observation (e.g., a week, month, year, or other time period) in a population at risk. o Population at risk  The members of the population who are capable of developing the disease or condition being studied are known as the population at risk.  E.g. only women with an in tact uterus are counted in the population “at risk” of uterine cancer