wk1 intro for epi - Epidemiology Learning Objectives for...

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Unformatted text preview: Epidemiology Learning Objectives for the Unit Having completed this unit, the student should be able to: Define epidemiology and list its uses Describe the key features of epidemiology Describe the basic measures used in epidemiology Calculate measures of disease frequency Interpret epidemiological data Define and calculate measures of association Learning Objectives for the Unit Describe study types used in epidemiology Identify the major sources of bias in research studies Define the keys elements of a health surveillance system Describe the key aspects of an outbreak investigation Assess information on the effectiveness of screening programs Assess the overall quality of a published report of an epidemiological study Unit 4 credit points Average student input per week: 5-6 hours Lectures (2 hours each week) Tutorials (1 hour each week). It is expected that students will attend classes. Assessment Sectional Test Group Assignment (2 hours) Week 9 Week 12 25% 25% 50% Final Examination Week 15/16 All assessments must be completed and submitted to pass the unit. Text Gordis, L. Epidemiology. WB Saunders Co., Philadelphia, 2004 (3rd Edition) Other Readings Contact details Dr Aditi Dey Room T337, Level 3, T Block Phone 9351 9058, 9351 9494 Email [email protected] Lecture Outline Introduction Population Health & Disease Measures Causation and Epidemiological Study Types Cohorts and Case- Control Studies and measures of association Randomised Controlled Trials Ecological studies and Cross Sectional Surveys Lecture Outline Sources of Error: Confounding Selection & Measurement Health Surveillance Disease Outbreaks Critical Appraisal Screening Using Epidemiology to Evaluate Health Services/Review Learning Objectives for today Define epidemiology List the uses of epidemiology Describe key historical epidemiological studies Explain the key features of epidemiological studies Origin of the term `epidemiology' epi - `on, upon, at, by, near, over, on top of, against, among' demos - `common people or citizenry' ology - `the study of' epidemiology =`Study of disease among the population' Definition of Epidemiology `study of the distribution and determinants of health related states or events in specified populations and the application of this study to the control of health problems' Last, 1995 Epidemiology is about Populations Groups of people not individuals It answers population questions aetiology of disease prevention of disease Extent/distribution of disease (allocation of effort & resources in health facilities and communities) Epidemiology and Clinical Practice Practice of medicine is dependent on population data. For example: A physician hears a apical systolic murmur and knows it represents mitral regurgitation. How does this knowledge originate? The diagnosis is based on association of auscultatory findings with the findings of surgical pathology or autopsy in a large group of patients. Hence, diagnosis is population based Example: Prognosis A patient may ask a doctor, "How long will I live?'' The doctor usually answers on the basis of : Experience with large groups of patients who had the same disease Were observed at the same stage of disease and received the same treatment Relationship between Epidemiology and Clinical Medicine Diagnosis Treatment Cure Care Studies/Assessments Prevention Evaluation Planning Examples of Epidemiological Studies (Use of observational data for prevention of disease) Vaccination: Prevention of smallpox Edward Jenner observed that dairy maids (women who milked cows) developed a mild disease called cowpox. Later, in outbreaks of smallpox, these dairy maids did not develop smallpox and overheard one of them say, "I can't take smallpox for I already had the cowpox.'' This information was observational. Jenner decided to test the hypothesis that cowpox could provide protection against smallpox. Examples of Epidemiological Studies Vaccination Edward Jenner & the smallpox vaccination First vaccination Jenner took cowpox material from a dairy maid (Sarah Nelmes) and administered to an 8year old James Phipps 6 weeks later, Jenner inoculated the child with material now taken from a smallpox pustule. The child did not develop smallpox Jenner knew nothing about the biology of the disease or about viruses He based his hypothesis from purely observational data Examples of Epidemiological Studies 1854 Outbreak of Cholera in London: sign at cemetery in Dudley, England Epidemiology of cholera John Snow and epidemiology of cholera John Snow: anaesthesiologist who administered chloroform to Queen Victoria in childbirth In the 1st week of September, 1854 about 600 people died from cholera. These people lived within a few blocks of the Broad Street pump in London Cholera outbreak map John Snow believed that cholera was caused by contaminated water (others had other theories: miasmatic theory) In London at that time, a person obtained water by signing up with one of the water supply companies. The intake for the water companies was a very polluted part of Thames river. One of the companies (Lambert Company) shifted its water intake upstream in the Thames to a less polluted part of the river but the others didn't. Snow hypothesised that: mortality from cholera would be lower in people getting water from Lambert Company than those getting water from other companies Rates of cholera deaths Water Supply Southwalk & Vauxhall Lambeth Co Other districts in London Cholera Deaths per 10,000 houses 315 38 56 The Broad Street pump After the panic stricken officials followed Snow's advice to remove the handle of the Broad Street Pump that supplied the water to this neighbourhood, the epidemic was contained. Examples of Epidemiological Studies Link between smoking and lung cancer Doll & Hill, 1964 Examples of Epidemiological Studies Water fluoridation: Communities that had low natural water fluoride levels had high levels of dental caries Communities that had high natural water fluoride levels had low levels of dental caries Trial in New York communities: Newburg and Kingston DMF (decayed, missed and filled) index was used. Baseline information from both communities collected Water in Newburg was fluoridated and children reexamined DMF index in Newburg had dropped after 10 years Rate of decayed teeth regional differences Water fluoridation is a controversial issue so after fluoride was added to its water supply, it was discontinued after a referendum in Wisconsin (USA) The next figure shows that after fluoride was removed, the DMF index rose This provided further evidence that fluoride acted to prevent dental caries Decayed teeth after fluoridisation Epidemiological Questions When can we expect the next flu epidemic? Are the number of AIDS cases increasing or decreasing? Should we screen the male population for prostate cancer? How can cervical cancer best be prevented? Has the slip, slap, slop campaign reduced skin cancers rates? Uses of Epidemiology(Gordis, 2000) Identifies aetiology or causes of disease including the risk factors for the disease. Determine the extent of the disease in the community Examines natural history of disease and prognosis of disease Investigates and controls disease outbreaks Uses of Epidemiology(Gordis, 2000) Describes and monitors the population health and the patterns of disease Evaluates new preventive and therapeutic interventions and modes of health care delivery Provides information to inform public policy decisions Identifies aetiology or causes of disease including the risk factors for the disease. Doll and Hill,1964 Determine the extent of the disease in the community NSW Health Survey,1997 Examines natural history of disease and prognosis of disease Figure 1: The Natural History of NIDDM Modifiable: Poor glucose control Inactivity Obesity Fat Intake Hypertension Dyslipidaemia Poor Footcare Smoking Non-Modifiable: Genetics Disease Duration Onset of complications Onset of NIDDM (Often asymptomatic) Population at Risk Primary Prevention Increase Activity Improve Nutrition Weight Control Manage NIDDM Glucose Control Education Increase Activity Reduce Obesity Diet Modification Treat Hypertension Treat Hyperlipidaemia Self care Reduce Smoking Ongoing Screening for complications Eyes Feet CVD Kidneys Treat Complications Glucose Control Education Increase Activity Reduce Obesity Treat Hypertension Treat Hyperlipidaemia Treat Retinopathy Treat Vascular Problems Self care Reduce Smoking Rehabilitation and Palliation Dialysis Post Amputation Rehab Cardiac Rehab Stroke Rehab Aids Support Risk Factors Modifiable: Inactivity Obesity Non-Modifiable: Genetics Age Modifiable: Undiagnosed onset of complications Untreated progression of complications Poor glucose control Hypertension Dyslipidaemia Poor Footcare Smoking Non-Modifiable: Genetics Natural History of NIDDM Healthy Population Development of End-Stage Complications (Blindness, ESRF, Heart Attack, Amputations) Possible Intervention Points Screen for NIDDM in at risk populations Investigates and controls disease outbreaks Describes and monitors the population health and the patterns of disease NSW Cancer Registry, 2002 Describes and monitors the population health and the patterns of disease breast cancer NSW Cancer Registry, 2002 Evaluates new preventive and therapeutic interventions and modes of health care delivery Has growth of managed care and other new approaches to health care delivery had an impact on the patients' QOL? Does screening women with MRI for breast cancer improve survival for women? Provides information to inform public policy decisions Smoking in restaurants Smokefree Environment Bill, 2000 NSW Health Survey,1997 Determining Causation Disease has been classically described as a result of an epidemiological triad It is the product of an interaction of the human host, an agent (eg infectious) and the environment that promotes the exposure For such an interaction to occur, the host must be susceptible Determining Causation Agent(s) eg microorganisms, chemicals, psychological factors Agent Disease Environment Host Environment Factors physical, social or biological environment circumstances Host Factors susceptibility eg immunity, behaviours Vectors of diseases: insects such as mosquitoes, arthropods (ticks) etc Determining Causation Infection Agent: Beta-haemolytic streptococcus Disease Host: Low immunity Environment Poverty, climate Disease: Acute rheumatic fever (polyarthritis, subcutaneous nodules over bony prominences, myocarditis which may cause acute cardiac failure & endocarditis) Determining Causation Chronic Disease - can be more complex - usually the result of many factors (referred to as risk factors) acting in sequence, or together that result in disease in an individual. Causal Pathway or Causal Web Source: Stallones, R.A. (1966) Risk Factor is: An aspect of personal behaviour or Lifestyle or environmental exposure or an inborn or inherited characteristic that is associated with an increased occurrence of disease or other health related event or condition. Risk Factor (major categories) BEINGS model by Jekel et al 2001 Biological & behavioural factors Environmental factors Immunological factors Nutritional factors Genetic factors Services, Social & Spiritual factors Defining Populations in Epidemiology Epidemiology focuses on defined population and measures disease outcomes & health in relation to a population at risk Population at Risk = People, healthy or sick have potential to develop a particular health state or illness. They would be counted as cases if they had the disease being studied In a survey of hang-gliding accidents it was Example recommended that flying should be banned between 11am and 3pm because this was when the greatest number (86%) of accidents occurred During the month of May 1995: 200 hang-gliders flew between the hours of 11am and 3pm 50 accidents occurred during this time 10 people flew outside the hours of 11am & 3pm 8 accidents occurred during this time Given this information, determine what time you are most likely to have an accident? Example Accidents during 11am and 3pm 50 accidents per 200 people gliding 1 in 4 people = 25% Accidents outside the hours of 11am & 3pm 8 accidents 10 people flew occurred during this time 4 in 5 people = 80% Types of Populations Population at Risk = People, healthy or sick who have the potential to develop a particular health state or illness. cohort or Populations may also be defined as: dynamic populations Cohort Populations Also called fixed populations Criteria for membership: experienced an event or set of events Once the qualifying events have been experienced by the person, membership of the cohort becomes a permanent Examples: a birth cohort may consist of all people born in 1973; people who have a tertiary degree. Dynamic Population Have to meet certain criteria to be part of the population Membership only lasts while the qualifying criteria are present, membership may be only temporary Examples: people attending university membership is temporary Dynamic Population Can be in a steady state when a specific feature remains constant despite changing membership. Example: Are people in clinical trials a cohort or dynamic population? if 51% of a dynamic population is female and this remains constant over time (eg some women die and some women are born) the population has a steady state in respect to gender composition Key components of epidemiological studies Target Population Exposure to a study factor Study Population/ Sample Exposed Outcome Unexposed Key components of epidemiological studies Target population is the population a researcher wants to make generalizations about Study population is the group a researcher wishes to study (sometimes the same as the target population) Study sample is a group of subjects chosen for study to represent the study population Key components of epidemiological studies Target Population Exposure to a study factor Study Population/ Sample Exposed Outcome Unexposed Key components of epidemiological studies Study factor is a element that is being investigated to see if it is a determinant of a particular health problem or if it reduces the impact of a particular health problem. Study factors can include risk factors for a health problem, interventions (therapeutic or preventative) to ameliorate a health condition, diagnostic tests or techniques and environmental exposures. Exposure is contact with or possessing a particular study factor Exposed group is a group whose members have had contact with or possess a study factor Key components of epidemiological studies Unexposed group is a group that has not had contact with a cause of, or possess a characteristic that is a determinant of, a particular health problem. Outcome is any or all of the possible results that may stem from an exposure or study factor. Conclusions Based on Comparisons Clues to aetiology come from comparing disease rates in groups with differing levels of exposure Clues will be missed or false clues created if comparisons are biased by unequal collection of cases or exposure levels Proportion of Deaths Attributable to Tobacco, NSW, 19961998 (Close & Achat) Cause of Death Western Sydney NSW Lung Cancer Other cancer Coronary heart disease Respiratory disease 31.3 8.5 22.9 24.9 29.3 9.0 20.6 27.7 Next week Population Health and Disease Measures incidence prevalence death rates standardisation Text: P31-59 ...
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This note was uploaded on 04/08/2008 for the course HIMT 3055 taught by Professor J during the Three '08 term at University of Sydney.

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