Principles of Epidemiology and Disease Surveillance PDF

PRINCIPLES OF EPIDEMIOLOGY AND DISEASE SURVEILLANCE INTRODUCT ION TO EPIDEMIOL OGY 2 OUTLINE ▪Introduction ▪Historical development ▪Definition ▪Scope and application ▪Basic principles and methods 3 INTRODUCTION Objectives of the course ▪To acquir...

PRINCIPLES OF EPIDEMIOLOGY AND DISEASE SURVEILLANCE INTRODUCT ION TO EPIDEMIOL OGY 2 OUTLINE ▪Introduction ▪Historical development ▪Definition ▪Scope and application ▪Basic principles and methods 3 INTRODUCTION Objectives of the course ▪To acquire basic knowledge, tools and skills on epidemiology, essential for the practice of public health ▪To use the knowledge, tools and skills to plan, manage, monitor and evaluate the success or failure of public health activities ▪To understand how epidemiological principles apply to your own area of study 4 INTRODUCTION ▪Epidemiology is the basic science/cornerstone of public health ▪It is data- driven and involves a systematic and unbiased means of collecting, collating, analyzing and interpreting data in order to draw conclusions ▪It involves a method of causal reasoning based on formulating and testing hypotheses ▪An idea or explanation that is based on a few known facts but has not yet been shown to be true is called a hypothesis (Speculation) 5 HISTORICAL DEVELOPMENT ▪The word epidemiology has Greek origin ▪Epid: Upon or on ▪Demos: People ▪Logos: Study of ▪Initially applied to studying epidemics but subsequently being applied to studying diseases (communicable and non-communicable) and health-related events 6 HISTORICAL DEVELOPMENT There are four main epochs/ historical periods ▪Period of relating diseases to the environment ▪Period of counting numbers ▪Period of natural experiments ▪Period of experimental epidemiology 7 HISTORICAL DEVELOPMENT Period of relating diseases to the environment Hippocrates (460-375 BC, Island of Cos, Greece) ▪Greek physician ▪Father of modern medicine and considered as the first epidemiologist ▪Condiererd as first to draw distinction between “epidemic” and “endemic” ▪He related diseases with the environment 8 INTRODUCTION ▪Postulated that medical investigations should take the seasons, the sun's rising and setting, water supply, and human habits into account (eating, indolence, exercise, labour) ▪Hippocrates thought that an imbalance of the some humours (air, water, fire, earth atoms) was the root cause of illness in humans ▪Hippocrates is presumed to have written “Of the Epidemics” around 400 BC, and “On Airs, Waters, and Places” 9 HISTORICAL DEVELOPMENT Period of counting numbers John Graunt (1620- 1674) ▪English Statistician ▪Quantification of disease patterns ▪First to analyze bills of mortality in England and Wales (a record of weekly counts of christenings and deaths) ▪Published his findings in 1662 ▪ 10 HISTORICAL DEVELOPMENT ▪Graunt’s findings- High rates of infant mortality, an excess of male births and deaths, seasonal patterns of mortality, and the effects of the plague in London were all revealed by his analysis ▪He constructed the first life table- a statistical table that makes use of death rates of a cohort (group) of persons to determine the group’s average life expectancy 11 HISTORICAL DEVELOPMENT Period of natural experiments William Farr (1807-1883) ▪A Statistician ▪In 1839, first Registrar General, Office of Vital Statistics in Britain ▪Person-years concept ▪ICD- International Classification of Diseases ▪Herd immunity- general level of immunity to a specific disease in a community 12 HISTORICAL DEVELOPMENT Period of natural experiments William Farr (1807-1883 ▪Relationship between incidence and prevalence rates (Period Prevalence= Incidence X average duration of a disease) ▪Dose- response relationship- when changes in the level of a possible cause are associated with changes in the prevalence or incidence of the effect ▪Prospective and retrospective studies 13 HISTORICAL DEVELOPMENT Period of natural experiments John Snow 1813- 1858 ▪A British Physician, had administered chloroform to Quuen Victiria to ease labour pains in 1853 and 1857 ▪Widely considered the father of contemporary epidemiology ▪With others, founded the London Epidemiological Society 14 HISTORICAL DEVELOPMENT Period of natural experiments John Snow 1813- 1858 ▪Investigated London’s Broad Street pump cholera outbreak in 1854 which led to many deaths in the Soho neighbourhood. Using reasoning, graphs and maps, he demonstrated the effect of the contaminated water coming from the Broad Street pump ▪Grand Experiment- comparing waterborne cholera cases in two regions of the city—one receiving sewage-contaminated water and another receiving relatively clean water- 1954 15 HISTORICAL DEVELOPMENT Period of natural experiments Semmelweiss, Ignaz (1818- 1865) ▪Hungarian physician ▪He did an observational study at the Vienna General Hospital- Obstetric division ▪He had observed high maternal mortality rates 9.9% in the older of the two obstetric divisions- staffed by physicians and medical students, compared to the division staffed by only midwives which was 3.9% 16 HISTORICAL DEVELOPMENT Period of natural experiments Semmelweiss, Ignaz (1818- 1865) ▪He speculated that the high mortality was associated with the infectious agents introduced by medical studebts from autopsy rooms ▪He introduced the practice of handwashing with chlorinated water (May 1847) ▪This led to drop in mortality to 1.9% in both divisions 17 HISTORICAL DEVELOPMENT Period of natural experiments Doll and Hill (1950s) ▪Correlation between smoking and lung cancer among British doctors (association between number of cigarettes smoked per day and annual lung cancer deaths) 18  HISTORICAL DEVELOPMENT Period of experimental epidemiology James Lind (1716- 1794) ▪Scottish physician ▪Conducted one of the forst ever clinical trials ▪Studied effect of administration of diet containing lemon on the incidence of scurvy- A disorder arising from lack of vitamin C, characterized by general weakness, anaemia, gum disease, and skin bleeding ▪His reported experiment on board a naval ship in 1747 showed that oranges and lemons cured scurvy 19 HISTORICAL DEVELOPMENT Period of experimental epidemiology Edward Jenner (1749- 1823) ▪English physician and scientist ▪Vaccine pioneer, developed small pox vaccine- first vaccine in the world ▪Showed that cowpox offered immunity against small pox 20 - Public health is defined by CDC as “organized community efforts aimed at the prevention of disease and the promotion of health. It links many disciplines and rests upon the scientific core of epidemiology.” - Epidemiology is the basic science of Public Health - It is the study of the distribution of health outcomes or disease within populations - And Factors that determine spread of health outcomes and diseases - Factors that determine whether someone gets a certain health outcome or disease are called risk factors. - The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of. Thus, the word epidemiology has its roots in the study of what befalls a population 21 DEFINITION The study of the distribution and determinants of health-related states and events in a specified population and the application of the study to the control of health problems. (John Last, 1988) 22 DEFINITION ▪Distribution- frequency, time, magnitude, pattern, person ▪Determinants- aetiology ▪Deterrents- interventions that can prevent or cure the disease and their effectiveness 23 Health states or events usually refer to infection, illness, disability, or death but may equally be used to refer to a positive outcome (e.g. survival). Epidemiological studies describe the distribution of these health outcomes in terms of frequency and pattern. The frequency is the number of occurrences of an outcome within a given time period, and the pattern refers to the occurrence of the outcome by time, place and personal or population characteristics. Determinants influence the frequency and pattern of health outcomes and are known as risk factors or protective factors, depending on whether they result in a negative or positive health outcome respectively. Epidemiological research also involves the testing of preventive interventions (e.g. vaccines, improved hygiene)and therapeutic interventions (e.g. medicines, surgery) to improve health and survival. An intervention may be evaluated either under ideal (research-controlled) conditions to assess its effi cacy or through a routine delivery system to assess its effectiveness. 24 Distribution. EPDM relates the frequency and pattern of health events and outcomes in a population of interest: Frequency refers to the number of health events, such as the number of cases of chicken pox or cholera or diabetes in a population, and 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 person, time, and place. Time patterns are those found in particular periods of time influencing the occurrences of injury or disease, such as annual, seasonal, weekly, daily, hourly, weekday versus weekend, and so on. Place patterns include geographic variations, urban versus rural differences, and location of work sites or schools. 25  Personal characteristic patterns include demographic factors that are or may be related to the risk of illness, injury, or disability, such as age, gender, marital status, and socioeconomic status, as well as behaviors and environmental exposures. Determinants. Determinants are factors—whether events, characteristics, or other things—that bring about a change in health conditions or other defined characteristics. In this area of investigation, the causes of diseases are closely studied, identified, and correlated with expected and measured health outcomes. Health-related states or events: Communicable diseases (such as cholera), Noncommunicable infectious diseases(such as Diabetes), injuries, chronic diseases, maternal–child health and birth defects, environmental health, and occupational health. 26 DEFINITION Epid is about studying risks and making inferences ▪Risk to individuals ▪Risk to populations/communities ▪Behaviours or exposures predisposing to risks of particular diseases ▪Drawing inferences based on risk studies 27 DEFINITION ▪Everyone is an amateur epidemiologist ▪We all take decisions daily based on risk 28  SCOPE AND APPLICATION Aims ▪To describe distribution of disease and health-related conditions ▪To identify etiological factors in the pathogenesis of disease ▪To provide data essential for planning, implementation and evaluation of the prevention and control of disease, and health conditions ▪To control, eliminate or eradicate diseases or health conditions using effective strategies 29 SCOPE AND APPLICATION Uses of epidemiology ▪Description of the health status of population (determining variations in disease pattern over time, and between places and persons) ▪Determinants of health, diseases and health conditions (studying exposures or behaviours and they increase or decrease risks of developing diseases or health conditions) 30 SCOPE AND APPLICATION Uses of epidemiology ▪Discover the agent, host and environment factors that affect health; Description of the natural history of diseases(across the spectrum of progression from health to sub-clinical changes to clinical signs/symptoms and recovery/death) ▪Determine the relative importance of causes of illness, disability and death ▪identify those segments of the population that have the greatest risk from specific causes of ill health ▪Achieving disease control, elimination or eradication ▪Determining outcomes of health interventions and services (effectiveness, acceptability) in improving population health ▪Provides basis for formulating public health policies ▪For disease classification; 31 SUMMARY...USES OF EPID. Population or Community health Assessment: To set policy and plan programs, public health officials must assess the health of the population or community they serve and must determine whether health services are available, assessible, effective, and efficient; Immunization uptake efficiency to combact vaccine preventable diseases, evaluation of the use of technological innovations on vaccine uptake...improving immunization coverage. Hence, the need to ask: What are the actual and potential health problems in the community? Where are they? Who is at risk? Which problems are declining over time? Which ones are increasing or have the potential to increase? How do these patterns relate to the level and distribution of services available ? Individual decisions: Change in lifestyle, behavious... Walking instead of taking a bus, stop smoking and taking of canned drinks, choosing a method of contraception instead of another, Abstinece. We are influenced, consciously or unconsciously by epidemiologists Completing the clinical picture: Study of outbreaks, epidemiologists contribute to understanding the natural history of diseases: HIV, smoking and lung cancer, pulmonary and heart disease, cervical cancer.... Search for causes: search for factors which influence one’s risk of disease so that appropriate public health action can be taken e. brand of tampon was linked by epidemiologist to toxic shock syndrome. Laboratory scientists and epidemiologists collaborating to provide evidence needed to establish causation 32 BASIC PRINCIPLES AND METHODS Strategies ▪Surveilance ▪Research 33 THE EPIDEMIOLOGIC/PUBLIC HEALTH APPROACH Surveillance: What is the Problem? Problem Risk Factor identification: What is the Cause? Intervention Evaluation: What works? Implementation: How do you do it Response 34 BASIC PRINCIPLES AND METHODS Epidemiological reasoning progression ▪Suspicion ▪Hypothesis formulation ▪Hypothesis testing and evidence validation ▪Action: Interventions, policies... 35 Case Definition: is a set of standard criteria for deciding whether a person has a particular disease or other health-related condition. By using a standard case definition we ensure that everyt case is diagnosed in the same way regardless of when or where it occurred. Cluster: group of cases in a specific time ad place that might be more than expected EPIDEMIC or OUTBREAK: disease occurence among a population that is in excess of what is expected in a given time and place ENDEMIC: disease or condition present among a population at all times PANDEMIC: a disease or condition that spreads across regions RATE: number of cases occurring during a specific period; always dependent on the size of the population during that period. 36 BASIC PRINCIPLES AND METHODS Methods ▪Descriptive (What or what magnitude?) ▪Analytic (What is the cause?) ▪Risk (How much harm can this exposure cause?) ▪Prognosis (How long has the sufferer got?) ▪Effectiveness (What is the best treatment?) ▪Value for money (What provides the best outcome for the least cost?) 37  BASIC PRINCIPLES AND METHODS Methods Descripitive: Descriptive EPDM: It covers time, place, and person. It may be summarized in terms of the “five Ws”: What = health issue of concern Who = person Where = place When = time Why/how = causes, risk factors, and transmission modes(determinants) ▪Ecological ▪Cross-sectional ▪Survey ▪Prevalence study 38 BASIC PRINCIPLES AND METHODS Methods Analytical; analytic EPDM is concerned with the search for causes and effects, or the why and the how. It seeks to quantify the association between exposures and outcomes and to test hypotheses about causal relationships ▪Case-control ▪Cohort 39 In an experimental study, the investigator determines through a controlled process the exposure for each individual (in a clinical trial) or community (in a community trial), and then tracks the individuals or communities over time to detect the continuing effects of the exposure. Intervention Studies ▪Clinical trials ▪Field trials ▪Community trials 40 REFERENCES Epidemiology lecture notes https://www.cdc.gov/training-publichealth101/php/training/introduction-to-epidemio logy.html Principles of Epidemiology: An Introduction to Applied Epidemiology and Biostatistics. Second Edition. It is available at: http://www.phppo.cdc.gov/PHTN/catalog/pdffile/Epi_Course.pdf 41 THANK YOU 42