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Chapter 2

Chapter 2. Practical Applications of Epidemiology. Seven Uses of Epidemiology. To study the history of the health of populations. To diagnose the health of the community. To study the working of health services-operations research.

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Chapter 2

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  1. Chapter 2 Practical Applications of Epidemiology

  2. Seven Uses of Epidemiology • To study the history of the health of populations. • To diagnose the health of the community. • To study the working of health services-operations research. • To estimate the individual risks of disease and other conditions.

  3. Uses, continued... • To identify syndromes. • To complete the clinical picture of chronic diseases. • To search for causes of health and disease.

  4. Historical Use of Epidemiology • Refers to the study of past and future trends in health and illness. • Secular trends--changes in disease frequency over time.

  5. Examples of Trends • Chronic diseases have replaced acute infectious diseases as the major causes of morbidity and mortality. • Leading causes of U.S. deaths are heart disease, cancer, and stroke.

  6. Factors Affecting Reliability of Observed Changes • Lack of comparability over time due to altered diagnostic criteria. • Aging of the general population. • Changes in the fatal course of the condition.

  7. Four Trends in Disorders • Disappearing • Residual • Persisting • New epidemic

  8. Disappearing Disorders • This category refers to conditions that were once common but are no longer present in epidemic form; an example is smallpox.

  9. ResidualDisorders • Conditions for which the key contributing factors are largely known. • Methods of control not implemented effectively. • Examples: STDs, alcohol abuse, tobacco use.

  10. Persisting Disorders • Diseases for which there is no effective method of prevention or no known cure. • Examples: certain types of cancer.

  11. New Epidemic Disorders • Diseases that are increasing in frequency. • Examples: lung cancer, HIV.

  12. Predictions About the Future • About 20 percent of the U.S. population in 2030 will be age 65 and older. • The need for health- and aging-related services will grow.

  13. Population Dynamics • Three factors that affect the size of populations are births, deaths, and migration. • When these factors do not contribute to net increases or decreases, the population is in equilibrium.

  14. Population Terms • Fixed population--adds no new members and, as a result, decreases in size due to deaths only. • Dynamic population--adds new members through migration and births or loses members through emigration and deaths.

  15. Demographic Transition • Shift from high birth and death rates found in agrarian societies to lower birth and death rates found in developed countries.

  16. Steady Population • A population is in steady state when the number of members exiting equals the number entering.

  17. Epidemiology and the Health of the Community • Provides a key to the types of problems requiring attention. • Determines the need for specific health services.

  18. Demographic and Social Variables • Age and sex distribution • Socioeconomic status • Family structure • Racial, ethnic, and religious composition

  19. Variables Related to Community Infrastructure • Availability of social and health services • Quality of housing stock • Social stability (residential mobility)

  20. Health-Related Outcome Variables • Homicide and suicide rates • Infant mortality rate • Selected mortality rates • Drug and alcohol abuse rates • Teen pregnancy rates • Birth rate

  21. Healthy People 2010, Goal 2 • “ . . . To eliminate health disparities among segments of the population, including differences that occur by gender, race, or ethnicity, . . .”

  22. Epidemiology and Policy Evaluation • Using epidemiologic methodologies to evaluate public health policies • Examples: tobacco control policies, drug treatment systems, food sold to schoolchildren

  23. Operations Research (OR) • The study of the placement and optimum utilization of health services in a community.

  24. Epidemiology and OR • Methods for selecting target populations • Data analysis techniques • Research designs • Measurement procedures

  25. Program Evaluation • Uses epidemiologic tools to determine how well a health program meets certain stated goals.

  26. Examples of OR • Coordination of programs for the developmentally disabled • Studies of health care utilization • Minority access to health insurance

  27. Epidemiology and Disease Etiology • Applications include: • Search for causes • Individual risks • Specific clinical concerns

  28. Modern Concepts of Causality • Five criteria for causality (source: 1964 Surgeon General’s Report): • Strength of association • Time sequence • Consistency upon repetition • Specificity • Coherence of explanation

  29. Further Consideration of Causality • Sir Austin Bradford Hill expanded the list of criteria to include: • Biologic gradient • Plausibility • Experiment • Analogy

  30. Risk Factors • Due to the uncertainty of “causal” factors the term risk factor is used. • Definition: exposure that is associated with a disease. • Example of a risk factor: smoking.

  31. Three Criteria for Risk Factors • The frequency of the disease varies by category or value of the factor, e.g., light smokers vs. heavy smokers. • The risk factor precedes onset of the disease. • The observation must not be due to error.

  32. Etiologic Study Designs • Case control • Cohort

  33. Case Control Design • A type of design that compares persons who have a disease (cases) with those who are free from the disease (controls). • This design explores whether differences between cases and controls result from exposures to risk factors.

  34. Cohort Design • A group of people free from a disease is assembled according to a variety of exposures. • The group (cohort) is followed over a period of time for development of disease.

  35. How Results Impact Clinical Decisions • The following considerations determine a study’s influence: • Criteria of causality • Relevance to each patient • Size of the risk • Public health implications • Individual vs. population

  36. Natural History of Disease • Prepathogenesis--before agent reacts with host. • Pathogenesis--after agent reacts with host. • Later stages include development of active signs and symptoms. • Clinical end points are: recovery, disability, or death.

  37. Primary Prevention • Occurs during prepathogenesis phase. • Designed to reduce the occurrence of disease. • Examples are education and immunization.

  38. Secondary Prevention • Occurs during pathogenesis phase. • Designed to reduce the progress of disease. • Examples are screening programs for cancer and diabetes.

  39. Tertiary Prevention • Designed to limit disability from disease. • Also directed at restoring optimal functioning. • An example is physical therapy for stroke patients.

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