Introduction to Epidemiology PDF

Introduction to Epidemiology Lissa Luz C. Calimag, MD, MPM-HSD, DFM Objectives At the end of the session, the participants shall be able to: 1. Define epidemiology 2. Identify selected activities performed in epidemiology 3. Explain the importance and application of epidemiology in the practice...

Introduction to Epidemiology Lissa Luz C. Calimag, MD, MPM-HSD, DFM Objectives At the end of the session, the participants shall be able to: 1. Define epidemiology 2. Identify selected activities performed in epidemiology 3. Explain the importance and application of epidemiology in the practice of medicine 4. Understand the basic vocabulary used in epidemiology Epidemiology Study of the distribution and determinants of health-related states or events in human populations and the application of this study to the prevention and control of health problems Greek epi meaning “on, upon, or befall”, demos meaning “the people” and logos meaning “the study of” Epidemiology Epidemiologic investigations involve descriptive and analytic methods that draw on statistical techniques for describing data and evaluating hypotheses, biological principles, and causal theory. Epidemiology Disease is not randomly distributed throughout a population, but rather that groups differ in the frequency of various diseases. Knowledge of this uneven distribution can be used to investigate etiologic factors and to lay the groundwork for programs of prevention and control Historic Developments of Epidemiology Hippocrates 460-377BC Father of medicine First epidemiologist Observations on how diseases affected populations and how disease spread Introduced terms like epidemic and endemic James Lind Book: A Treatise on Scurvy (1754) Identified the symptoms of scurvy and the fact that the disease became common in sailors after as little as a month at sea Clinical Trial in Scurvy (James Lind) 12 ill patients who had all of the classic symptoms of scurvy were assigned different supplemental dietary interventions: A quart of cider a day on an empty stomach Two spoonfuls of vinegar three times a day on an empty stomach Half-pint of sea water every day Lemons and oranges to eat on an empty stomach Elixir recommended by a hospital surgeon Combination of garlic, mustard seed, and horseradish John Snow Anesthesiologist for Queen Victoria of England Father of modern epidemiology Observed and recorded important factors related to the course of disease in cholera in the 1850s Spot Map by John Snow Comparison of two water companies by John Snow Compared death rates from the disease to where the sufferers got their water. The death rate was 71 per 10,000 in Southwark and Vauxhall households and 5 per 10,000 for Lambeth households. Lambeth was able to draw water free from London’s sewage. Proved his hypothesis that contaminated water passing down the sewers into the river, then being drawn from the river and distributed through pipes into people’s homes, produced cholera throughout the community. John Graunt 1620-1674 A systematic recording of deaths commenced and was called the “bills of mortality” Systematically recorded ages, gender, who died, what killed them, and where and when thedeaths occurred. Recorded how many persons died each year and the cause of death William Farr 1807-1883 Father of Modern Vital Statistics and Surveillance International Classification of Diseases Concepts and Terms in Epidemiology Broad Categories in Epidemiology Descriptive Epidemiology Study of the amount/frequency & distribution of disease, etc. in populations Analytic Epidemiology Study of the determinants or etiology of disease & related conditions Aim of Descriptive Epidemiology Permit evaluation of trends in health and disease Provide a basis for planning, provision, and evaluation of health services Identify problems to be studied by analytic methods and suggest areas that may be fruitful for investigation Descriptive Epidemiology For almost all diseases / illnesses, three basic epidemiologic questions may be asked: Who develops the disease? PERSON variables When does the disease occur? TIME variables Where does the disease occur? PLACE variables Descriptive Epidemiology Person – Age, Sex, Race and Ethnicity, Civil Status Place – Global, National, Local Time - Seasonal/Cyclic, Secular, Epidemic Activities in Epidemiology Identifying risk factors for disease, injury, and death Describing the natural history of disease Monitoring diseases and other health-related events over time Evaluating the efficacy and effectiveness of prevention and treatment programs Providing information that is useful in health planning and decision making for establishing health programs with appropriate priorities Assisting in carrying out public health programs Being a resource person Communicating public health information Uses of Epidemiology in Public Health Policy and Individual Decision-Making Assessment Identify who is at greatest risk for experiencing the public health problem Identify where the public health problem is greatest Identify when the public health problem is greatest Monitor potential exposures over time Monitor intervention-related health outcomes over time Uses of Epidemiology in Public Health Policy and Individual Decision-Making Cause Identify the primary agents associated with disease, disorders, or conditions Identify the mode of transmission Combine laboratory evidence with epidemiologic findings Uses of Epidemiology in Public Health Policy and Individual Decision-Making Clinical picture Identify who is susceptible to the disease Identify the types of exposure capable of causing the disease Describe the pathologic changes that occur, the stage of subclinical disease, and the expected length of this subclinical phase of the disease Identify the types of symptoms that characterize the disease Identify probable outcomes (recovery, disability, or death) associated with different levels of the disease Uses of Epidemiology in Public Health Policy and Individual Decision-Making Evaluate Identify the efficacy of the public health program Measure the effectiveness (considering cost, availability of resources, and feasibility) of the public health program Behavior of Disease in the Community Epidemic - occurrence of cases of an illness, specific health-related behavior, or other health-related events clearly in excess of normal expectancy in a community or region Outbreak - epidemic that is confined to a localized area Endemic - ongoing, usual, or constant presence of a disease in a community or among a group of people Pandemic - an epidemic affecting or attacking the population of an extensive region, country, or continent Behavior of Disease in the Community Behavior of Disease in the Community Case Concepts in Epidemiology Case - a person in a population who has been identified as having a particular disease, disorder, injury, or condition Case definition - standard set of criteria ensures that cases are consistently diagnosed, regardless of where or when they were identified and who diagnosed the case Primary case - the first disease case in the population Index case - the first disease case brought to the attention of the epidemiologist Triangle of Epidemiology (Traditional) Triangle of Epidemiology (Advanced Model) Disease Transmission Concepts Fomite - A fomite is an object that can harbor an infectious agent and is capable of being a means of transmission Vehicle - nonliving intermediary such as a fomite, food, or water that conveys the infectious agent from its reservoir to a susceptible host. Disease Transmission Concepts Vector - an invertebrate animal (e.g., tick, mite, mosquito, bloodsucking fly) that transmits infection by conveying the infectious agent from one host to another; mechanical or biological transmission Zoonosis - an infectious organism in vertebrate animals (e.g., rabies virus, bacillus anthracis, Ebola virus, influenza virus) that can be transmitted to humans through direct contact, a fomite, or a vector. Disease Transmission Concepts Reservoir - the habitat (living or nonliving) in or on which an infectious agent lives, grows, multiplies, and on which it depends for its survival in nature Carrier - a person who harbors the infective agent/s without showing signs of disease, but is capable of transmitting the agent to other persons. Modes of Disease Transmission Direct Transmission - the direct and immediate transfer of an infectious agent from one person to another. Requires physical contact between an infected host and a susceptible person, and the physical transfer of a pathogen. Ex: STD, perinatal mother-to-child, skin-to-skin Modes of Disease Transmission Indirect Transmission - an agent is transferred or carried by some intermediate item, organism, means, or process to a susceptible host, resulting in disease. Ex: Air currents, dust particles, water, food, oral–fecal contact, and other mechanisms Vector-borne, Vehicle-borne Airborne transmission – can be direct or indirect transmission Summary Description in epidemiology begins with the assumption that diseases do not occur at random. Pioneers of Epidemiology Typically, three standard questions are posed to characterize the nonrandom distribution of a disease: Who gets the disease? (person) Where does the disease occur? (place) When does the disease occur? (time)