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244531187-Epidemiology.pptx
- 1. Basic Epidemiology Concepts for Public Health and Community Health Assessment 1
- 2. Objectives 1. Define epidemiology (Epi) 2. Describe how epidemiology has developed over time 3. Describe the essential elements of Epi and an epidemiological approach 4. Explain the basic Epidemiological concepts 5. Differentiate between descriptive and analytical epidemiology 6. Explain how nurses use epidemiology in community health practice 7. Identify terms that are used to measure and characterize disease frequency in human populations 2
- 3. How is Public/Community Health Different From Medicine? • Public health is population- based • Medicine is based on the individual 3
- 4. 4 Epidemiology • The study of the distribution of health and illness and the factors that determine (determinants) the population’s health status
- 5. Purpose of Epidemiology • To search for causal relationships in health and illness • To control illness by understanding causality Goal: Preventing disease and maintaining health 5
- 6. History of Epidemiology • Jenner • Snow • Nightingale
- 7. Goals 7 Medical Care Individual Health Public Health Population Health Best outcome for individual Healthy community Balance of individual autonomy vs. limitations on individual Balance in allocation of resources Focus on prevention
- 8. Analytic Epidemiology • Investigates origins and causal factors • Looks at etiology • Looks at factors, exposures, characteristics and behaviors • Why are some affected more than others Example – Smoking……………
- 9. Analytic Epidemiology • Search for determinants of disease or injury • Research on cause-effect relationships that tests specific hypotheses: ▫ Case-control studies ▫ Cohort studies ▫ Randomized clinical trials 9
- 10. Descriptive Epidemiology • Looks at health outcomes in terms of who, what where, when and why. • Discusses diseases in terms of person, place and time. Example – H1N1 ………………
- 11. Descriptive Epidemiology • Studies the distribution of disease and other health-related states and events in terms of: ▫ personal characteristics, (person) ▫ geographical distribution (place), and ▫ temporal patterns (time). 11
- 12. Patterns Relative to Person • Age • Education • Race • Gender • Occupation • Income • Ethnicity • Behavior Person: Who has the lowest / highest disease rates in the population? 12
- 13. Descriptive Epidemiology: Patterns of Health Events Patterns Relative to Place • Where (place) is the health outcome occurring most frequently? 13
- 14. Patterns Relative to Place • Define in terms of traditional political boundaries ▫ States ▫ Counties ▫ Municipalities • Census track data/zip codes 14
- 15. Descriptive Epidemiology • geographic unit ▫ state ▫ county ▫ census tract 15 population density migration Place: Where are the lowest / highest disease rates for a population?
- 16. Example of Census Track Map 16
- 18. Descriptive Epidemiology • short-term trends • long-term or secular trends 18 cyclic trends age, period, and birth cohort effects Time: Are the disease rates changing over time for a population?
- 19. Patterns Relative to Time • Is the frequency of the health outcome changing over time? 19
- 20. Patterns Relative to Time • Annual trends • Seasonal occurrence • Daily or hourly changes 20
- 21. 21
- 22. Descriptive Epidemiology (DE) • Used to understand the pattern and frequency of health events in a population, e. g., childhood asthma 22 How often are kids hospitalized for asthma compared to other conditions? Which groups are at high risk for being hospitalized for asthma? Are childhood asthma hospitalization increasing or decreasing? Identify emerging problems and track known public health issues (CH Nurse)
- 23. Descriptive Epidemiology • Prioritize public health problems • Target resources and interventions • Provides information for policy and program development • Evaluate programs and practices • Advocate for additional resources ▫ Human Resources ▫ Financial and physical resources 23
- 24. Epidemiology: Two broad concepts • Control of health problems through an understanding of their contributing factors • Application of epidemiologic techniques to health-related conditions other than acute communicable disease 24
- 25. Epidemiology: Causality and Control • Health Outcomes are characterized in terms of: ▫ What is the outcome? ▫ Who is affected? ▫ Where are they? ▫ When do events occur? ▫ Why? 25
- 26. 26 Epidemiologic Triangle (Fig. 9-2, p. 167)
- 28. Epidemiologic Triangle (Box 9-1; p. 168) • Agent- animate or inanimate factor that must be lacking or present for a disease or condition to develop • Examples: ▫ Infectious agents: virus, bacteria ▫ Chemical agents: pesticides ▫ Physical agents: radiation, heat, machinery 28
- 29. Epidemiologic Triangle • Host – human or animal species capable of being infected and affected by an agent • Examples: ▫ Genetic susceptibility ▫ Age, sex ▫ Acquired characteristics (immunological status) ▫ Life style factors 29
- 30. Epidemiologic Triangle • Environment - all that is internal or external to a given host or agent and that is influenced and influences the host and/or agent • Examples: ▫ Climate ▫ Plant and animal life ▫ Socio economic status ▫ Populations – distribution and density 30
- 31. Determinants of health events • The determinants of health events refers to those factors, exposures, characteristics, behaviors, and contexts that determine or influence the patterns. ▫ How does it occur? ▫ Why are some affected more than others? Individual Relational or social Communal or environmental 31
- 32. Determinants • Focus is on investigation of causes and associations (analytic epidemiology) • Understanding the etiology or natural history of the disease 32
- 33. Distribution • Refers to patterns of health events in populations. • Health-related events in human populations : ▫ Diseases ▫ Conditions ▫ Injuries 33
- 34. CH Nurse and Epidemiology • Epidemiologist—a health detective who links observed problems with potential causes, to arrive at a diagnosis and design and implement a mitigating response. 34
- 35. How CHN Use Epidemiology • Identifying causative factors • Identifying risk factors • Diagnosing the health status of population groups • Describing S & S and the course of a disease • Evaluating the effectiveness of existing and proposed interventions and modes of health care delivery • Providing a basis for health policy 35
- 36. Epidemiologic Investigation • Three Basic Concepts: ▫ Causality ▫ Risk ▫ Rates of occurrence 36
- 37. Causality • One event is the result of another event • Theories of causation (single cause) ▫ Religious Era - disease caused by punishment ▫ Environmental Era – disease caused by harmful substances in the environment ▫ Bacteriologic Era – disease caused by specific organisms ▫ Current Era – multiple causation 37
- 38. Causality: Example • Important to know the potential for various sources of exposure • Evidence-based ▫ Lead: Paint Water pipes Contaminated Soil 38
- 39. Criteria for Determining Causality • Consistency of association • Strength of association • Specificity • Temporal relationship between events • Coherence with other known facts 39
- 40. Determining Causality: Criteria 1. Consistency of association ▫ Association between the factor in question and the problem must be consistent • Example: ▫ People can not develop measles without being exposed to the virus 40
- 41. Determining Causality: Criteria 2. Strength of association ▫ The greater the correlation between the occurrence of the factor and the health condition, the greater the association (cause and effect) • Example: ▫ Measles: some develop it some don’t 41
- 42. Determining Causality: Criteria • Strength of the association may reflect: ▫ Dose-response gradient - the greater the exposure to the presumed cause, the greater the likelihood of developing the problem (Gordis, 2000) 42
- 43. Criteria for Determining Causality 3. Specificity – present when the factor in question results in one specific condition • Example: exposure to the measles virus result only in measles not in mumps of chickenpox 43
- 44. Criteria for Determining Causality 4. Temporal relationship between events: ▫ Refers to the time relationship between the factor and the resulting condition • Example: one must be exposed to measles virus before, not after, one gets the measles 44
- 45. Criteria for Determining Causality 5. Coherence with other known facts: ▫ The idea that one condition causes another must be logical and congruent with other known facts. • Example: alcohol consumption and car accidents ▫ Increases the time required for voluntary muscles to react to stimuli ▫ Slow response to changing driving conditions ▫ Causative factor in many accidents 45
- 46. Epidemiological Key Terms (WHO) ▫ Epidemic: An outbreak of a contagious disease or condition that spreads rapidly and widely. 46
- 47. Epidemiological Key Terms • Endemic: of or relating to a disease (or anything resembling a disease) constantly present to greater or lesser extent in a particular locality; • Examples of endemic diseases/conditions: "endemic malaria“ in the tropics "food shortages and starvation are endemic in certain parts of the world“ Botulism in Alaska Cholera among some Asian/Pacific Islanders 47
- 48. Epidemiological Key Terms • Point epidemic: a time-and-space-related pattern which is an indicator for toxic exposures. ▫ Outbreak of a GI illness due to contaminated food • Example: E-coli infection due to contaminated spinach in summer 2007 in Western USA 48
- 49. Epidemiological Key Terms ▫ Pandemic - an epidemic that is geographically widespread or over a wide geographical area; occurring throughout a region or even throughout the world AIDS in Africa 49
- 50. Obesity Epidemic in US BMI>25% 50
- 52. 52
- 53. Measures of Morbidity and Mortality • Rates –Frequency of a health event • Proportions – Fraction of population affected • Risk –Probability that an event will occur
- 54. Rates (Rates of Occurrence) • Rates of occurrence are statistical measures that indicate the extent of health problems in a group • An expression of events relative to the size of the population in which they occurred. • Enables us to compare the risk of health events across different groups of people, places, and time periods 54
- 55. Types of Rates • Crude rates • Category-specific rates: age, gender, race • Age-adjusted rates • Prevalence rates • Incidence rates 55
- 56. Rates A measurement of the frequency of a health event in a specific population over a specific period of time • Mortality rate is expressed as an annual death rate or mortality rate from all causes: Total no. of deaths from all causes in 1 yr. X 1,000 No. of persons in the population at mid year
- 57. Expression of Rates • Rate is a measure of a part • A portion of the population experiencing an event • It is expressed per 1,000 people because that is easier to relate to 51 per 1,000 rather than 0.051 cases per person
- 58. Case Fatality Rate Case fatality is the number of people who die of a disease over the total number of people with the disease. Die from disease X 100 Total with disease Find the case fatality rate for 20 women diagnosed with ovarian cancer if 18 die in one year.
- 59. Crude Rates • Total number of events divided by total population • For mortality, crude rates can either be deaths from all causes OR cause-specific (e. g., deaths from coronary heart disease) 59
- 60. 60 Crude Rates: Total Mortality Place Total Death Population Rate per 100K Mercer Island (1991-95) 736 103,805 709.0 Snoqualamie Valley (1991-95) 707 157,750 448.2
- 61. Problem with Crude Rates • They don't account for underlying demographic differences AGE LOCATION TIME
- 62. 62 Age-adjusted rates • Age-adjustment is a statistical process applied to rates of disease, death, injuries or other health outcomes that allows communities with different age structures to be compared.
- 63. 63 Age-Adjusted Rates • Applies the observed age-specific rates to a standard population ▫ 1950 U.S. population ▫ 2000 projected U.S. population • Represents the hypothetical rate that would have been observed if the population of interest had the same age distribution as the standard population
- 64. What rates tell us • How quickly things are happening • How things are changing • Moving form one state of being to another
- 65. Proportion • Example: In 2008, there were 31,753,000 persons 65 or older in a population of 252, 177,000 31,753,000 __________ 252,177,000 = .126 or 12.6% 65
- 66. Deaths per live Births • A proportion that indicates the portion of a population who experience an event during some specified period of time, e.g. the annual infant mortality rate. 66
- 67. Incidence • The incidence of disease is the number of NEW cases of a disease that occur within a specified time period. • Expressed as a fraction: Number of new cases of a disease occurring in the population during a specified period of time ______________________________ X 1,000 Number of persons at risk of developing the disease during that time period
- 68. Incidence Rate • Example 1 • Incidence rate = 5 new people with a diagnosis of HIV= 0.50 • Population of 10 people • Example 2: • Incidence rate = 5 new people with a diagnosis of HIV= 0.05 • Population of 100 people • 5% or 5 of 100 people 68
- 69. 69 Incidence Rates • It is very important to know the number of new people infected with a disease (incidence) in relation to the total population at risk of contracting that disease *during a specified time period. *Point Prevalence
- 70. Incident Rates • Tell us 3 things The occurrence of NEW cases during a specified time period QUANITFIES the rate of development of NEW cases Tells us the probability that a person at risk will develop the disease
- 71. Prevalence Rates • Measures the presence of a disease or attribute in a population at a given time (Point Prevalence) • Probability that an individual in the population has a disease/condition 71
- 72. 72 Prevalence data • Provide an indication of the extent of a condition and may have implications to the provision of services needed in a community. • Prevalence is most useful for measuring the burden of chronic diseases such as tuberculosis, malaria and HIV in a population.
- 73. Calculate HIV Prevalence Rate • In 2003 (specific point in time) Clinic B gave service to 1000 patients (population at risk) • 200 of these patients were HIV + • The HIV prevalence rate among the clinic’s patients at the end of 2003: ▫ Existing # of pt. with HIV = 200 ▫ Divided by population at risk 1000 = 0.20 (20%) 73
- 74. 74 Examples of Prevalence Rates • Disease/violence risk factors (e.g., tobacco use, firearm ownership) • Health care access (e.g., health insurance coverage, unmet medical need) • Health screening (e.g., mammography. Pap test, cholesterol, blood pressure)
- 75. 75 The Relationship Between Prevalence & Incidence Prevalence Incidence (New Cases)
- 76. 76 Distinguishing between I & P* • Incidence gives us a barometer of how many new cases of a disease are being detected, • While prevalence gives us a barometer of how long people are living with a disease. *I: Incidence *P: Prevalence
- 77. 77 Hepatitis A Cases: Hypothetical Location # of Cases Time Period Annual Population Union County 33 1992-95 17,715 Essex County 44 1994-95 394,923 Where is the risk of Hepatitis A higher?
- 78. 78 Hepatitis B occurred more frequently in which County? Location # of Cases/Pop/Year Average Annual Rate Orange County 33/ 17,715/3 years (11 cases per year, on average) 62.1 / 100,000 people per year Dale County 55/394,923/3 years (22 cases over 2 years, on average) 46.4 / 100,000 people per year *When comparing rates in different places use the same time period for each place.
- 79. 79 • Public health surveillance is the ongoing collection and timely analysis, interpretation, and communication of health information for public health action • Public health surveillance systems are important tools for collecting and disseminating descriptive epidemiologic data Surveillance
- 80. 80 Surveillance Method • population-based • representative sample • convenience sample Example -- vital statistics -- BRFSS -- survey at local mall Different surveillance collection methods provide varying levels of confidence in the data.
- 81. 81 Sampling Types • Simple random sampling = every sampling unit has an equal chance of being sampled • Systematic sampling = every ith sampling unit is sampled
- 82. 82 Surveillance Vital Statistics • births • deaths Reportable Diseases • childhood • food borne • infectious • sexually transmitted
- 83. 83 Surveillance Registries • cancers • birth defects Surveys • NHIS • NHANES • BRFSS
- 84. 84 Surveillance Data on the Internet • Centers for Disease Control and Prevention (www.cdc.gov) ▫ CDC Wonder ▫ Behavioral Risk Factor Surveillance System • National Center for Health Statistics (www.cdc.gov/nchs)
- 85. 85
- 86. 86 National Center for Health Statistics (NCHS) • http://www.cdc.gov/nchs • What parts of this site are useful for fact lookup, research and indicators?
- 87. 87 Public Health Surveillance Loop Data Program Interpretation Evaluation Data Information Program Analysis Dissemination Implementation Data Program Collection Planning
- 88. 88 Screening • Screening is defined as the testing of groups of individuals who are at risk for certain conditions but are as yet asymptomatic. • CHN strategies ▫ Know latest guidelines ▫ Link to referral mechanisms ▫ Follow-up
- 89. 89 Screening Tools: Reliability • Reliability is the precision or reproducibility of a measure.
- 90. 90 Validity • In a screening test is measured in terms of the probability of correctly classifying an individual with regard to the disease or outcome of interest • Usually measured by sensitivity and specificity.
- 91. 91 Sensitivity • Quantifies how accurately the test identifies those with the condition or trait • Represents the proportion of persons with the disease whom the test correctly identified as positive (True Positive)
- 92. 92 Specificity • Indicates how accurately the test identifies those without the condition or trait • Represents the proportion of persons who do not have (without) the disease whom the test correctly identified as negative for the disease (True Negative)
- 93. 93 Sensitivity and Specificity • Determined by comparing the results from the test with results from a definitive diagnostic procedures ▫ Diabetes ▫ Pap smear • Combination of two or more tests are used to enhance sensitivity or specificity ▫ ELISA and Western Blot tests for HIV
- 94. 94 Series Testing • Used to enhance sensitivity or specificity • Sequence is important • The final result is considered positive only if all tests in the series were positive • It is considered negative if any test was negative • Series testing enhances specificity, producing fewer false positives, but sensitivity will be lower
- 95. 95 Applications of epidemiology in community and public health nursing. • Community-oriented nurses work in diverse settings and agencies, with a range of responsibilities. • The practice of community-oriented nursing is enhanced by the understanding and application of epidemiological concepts and methods.
- 96. 96 Applications of epidemiology in community and public health nursing. • Epidemiological measures are used to assess the health needs of a population. • Planning and implementation of health care services, interventions, and policies depend on understanding factors that influence health and disease and on the ability to evaluate interventions, programs, and policy.
- 97. Levels of prevention • Primary prevention involves interventions to reduce the incidence or prevent disease by promoting health and preventing disease processes from developing. • CHN Strategies: ▫ General Health Promotion Activities Health education Counseling ▫ Prevention Immunization 97
- 98. 98 Levels of prevention • Secondary prevention includes programs designed to detect disease in the early stages, before signs and symptoms are clinically evident, to allow early diagnosis and treatment. • CHN Strategies: ▫ Health screenings (community settings) ▫ Examples: Diabetes, cholesterol, skin cancer
- 99. 99 Levels of prevention • Tertiary prevention provides interventions directed toward persons with clinically apparent disease, with the aim of curing, ameliorating the course of disease, reducing disability, or rehabilitating. • Clinics, hospitals, homes
- 100. 100 Levels of Prevention: Examples • Primary- Discuss with client low-fat diet and the need for regular exercise • Secondary- Implement BP and cholesterol screening; give treadmill stress test • Tertiary- Provide cardiac rehabilitation, medication, out-patient post-cardiac surgery care, community exercise program
- 101. 101 Summary • Epidemiology: is a core component of public health, ▫ studies populations to understand causes of disease and to develop and evaluate effective interventions to prevent disease and maintain health. ▫ multidisciplinary enterprise, encompassing clinical medicine and laboratory sciences, quantitative methods, such as biostatistics, and public health policy and goals.
- 102. 102 Summary • Clinical medicine: ▫ focuses on the diagnosis and treatment of disease in individuals • Community and public health nursing: ▫ bridges these disciplines in its focus on individual clients and services, and in its use of epidemiological methods and findings in community health nursing practice.