1. Applications of Epidemiology in Communities

2. Epidemiology The study of the distribution of health and of the determinants of deviations from health in populations

3. Purpose of Epidemiology To obtain necessary data to prevent and control disease through Community Health Intervention Epi - “on or upon” Demos - “the people” Logos - “Knowledge”

4. Uses of epidemiology §study effects of disease states in populations over time and predict future health needs §diagnose the health of the community §evaluate health services §estimate individual risk from group experience

5. Uses of epidemiology (con’t) §Identify syndromes §complete the clinical picture so that prevention can be accomplished before disease is irreversible §search for cause

6. Epidemiologic investigations focus on: §Infectious disease §Non-infectious chronic conditions §Acute events §Emotional/Mental Health conditions §Normal characteristics of populations

7. 2 Models to describe the factors necessary to make an epidemiologic event happen §Web of Causation §Ecological (or epidemiologic) Model

8. Example of a Web of Causation Susceptible Host InfectionTuberculosis Vaccination Genetic Overcrowding Malnutrition Tissue Invasion and Reaction Exposure to Mycobacterium

9. Agent: Amount, infectivity, pathogenicity, virulence, chemical composition, cell reproduction Environment: Physical, biological, social Host: Intrinsic factors, physical factors, psychological factors, immunity Health or Illness ?

10. Examples of Agents of Disease §Nutritive excesses or deficiencies (Cholesterol, vitamins, proteins) §Chemical agents (carbon monoxide, drugs, ragweed, medications) §Physical agents (Ionizing radiation §Infectious agents (hookworm, amoebae, malaria, tuberculosis, syphilis, histoplasmosis, polio, rabies, mumps)

11. Examples of Host Factors §Genetic (Sickle cell disease) §Age §Gender §Ethnic group §Physiologic state (fatigue, pregnancy, puberty) §Prior immunologic experience (maternal antibodies, immunization, prior infection) §Intercurrent or preexisting disease §Human behavior (Food handling, diet, hygient, recreation, use of resources)

12. Examples of Environmental Factors §Physical environment (geology, climate §Biologic environment (population density, sources of food, influence of vertebrates and arthropods §Socioeconomic (exposure to chemical agents, urban crowding, tensions/ pressures, cooperative efforts in health education, wars, floods

13. Epidemiology within the U.S. Health Care System IndividualAggregate Curative Preventive Basic Nursing Community Health Nursing/Public Health MedicineEpidemiology

14. Levels of Prevention §Primary:Activities to decrease the probability of specific illnesses or dysfunctions No Disease Present §Secondary: Early Diagnosis and prompt intervention allowing early return to ADLs. Disease has occurred §Tertiary: A defect or disability is fixed, stabilized or irreversible. Rehabilitation. Disease has advanced

15. Natural History of Disease The process by which diseases occur and progress in humans

16. Natural History of Disease Primary Prevention Secondary Prevention Tertiary Prevention Pre-exposure Stage: Factors present leading to problem development Preclinical Stage: Exposure to causative agent: no symptoms present Clinical Stage: Symptoms present Resolution Stage: Problem resolved. Returned to health or chronic state or death Exposure to Agent Symptom Development

17. Epidemiologic Control Measures §Rapid identification of isolated disease outbreaks §Notification to local health authority l Local l District or state l National l WHO

18. Relative Risk (Risk Ratio) §The ratio of the risk of death among those exposed to a factor to the risk among those not exposed. = Incidence of disease in exposed group -------------------------------------------------- Incidence of disease in nonexposed group

19. Calculating Relative Risk Daily avg # drinksCirrhosis Cases (per 1,000) Relative Risk 07 126 2-348 4+40

20. Attributable Risk Attributable Risk: Rate of a disease among exposed individuals that can be attributed to the exposure and not to other causes rate of outcome (incidence or mortality) among exposed - rate among the unexposed per K

21. Calculating Attributable Risk Exposed Rate-Unexposed Rate =

22. Basic Definitions §Morbidity §Mortality §Epidemic §Endemic §Pandemic

23. Rates §Allows comparison between populations §Frequency in numerator §Comparison population in denominator §X/Y x K §Usually per 1,000 or 100,000 (NOT %)

24. Incidence # of new cases of disease in a place from Time 1 to Time 2 ___________________________________ x K # of persons in a place at midpoint of time period

25. Prevalence # of existing cases in a place at a given time _________________________________ x K # of persons in a place at midpoint of year

26. Crude Mortality Rate # of deaths during a year ___________________________ Average (midyear) population /per 100,000 population

27. Cause-Specific Mortality Rate # of deaths from a stated cause in a year _______________________________ Average (midyear) population /per 100,000 population

28. Age-specific mortality rate # of deaths of a given age group in a year ____________________________________ Average (midyear) population of same group /per 100,000

29. Standardized Mortality Rates Adjusts for differences in populations so that comparisons are interpretable. §Age-adjusted §Race-adjusted §Gender-adjusted

30. Maternal Mortality Rate # of maternal deaths during a year __________________________________ # of live births in same year per 100,000 live births

31. Infant Mortality Rate # of deaths of children < 1 year during a year __________________________________ # of live births in same year per 100,000 live births

32. Crude Birth Rate # of live births during year _____________________________ Total midyear population per 100,000

33. Case Fatality Percentage # of deaths from specific disease ___________________________ # of cases TIMES 100%

34. Interpreting Epidemiological Information §Indices of population change are fertility, mortality, and migration §Indices of overall health status are IMR and MMR §To plan for future health needs, look at age distribution, “at-risk” groups, screening protocols, treatment modalities, and referral mechanisms

35. Screening Validity §Sensitivity §Specificity §Positive and Negative Predictive Values

36. The Ideal Screening Test Normal Diabetic Blood Glucose

37. Sensitivity §Test’s ability to identify correctly those who do have disease §= True positives/All those with the disease §= TP /TP + FN

38. Specificity §Test’s ability to identify correctly those who do not have disease §= True negatives/All without the disease §=TN/ TN + FP

39. Indices to evaluate accuracy of Screen or diagnostic test TestDisease PresentDisease Absent Positive ResultA (True positives)B (False positives) Negative ResultC (False Negatives)D (True negatives) TotalsA+CB+D

40. Application of Sensitivity & Specificity Blood Glucose Level (mg/100 ml) using screening test Actual diabetics; n=70) Actual nondiabetics; n=510) 80 90 100 110 100.0 (n=1) 98.6 (n=1) 97.1 (n=3) 92.9 (n = 3) 1.2 (n=6) 7.3 (n=31) 25.3 (n=91) 48.4 (n=116) 120 130 140 150 160 170 180 190 200 88.6 (n=4) 81.4 (n= 5) 74.3 (n=7) 64.3 (n= 6) 55.7 (n= 3) 52.9 (n=2) 50.0 (n=4) 44.3 (n=5) 37.1 (n=26) 68.2 (n=101) 82.4 (n=71) 91.2 (n=45) 96.1 (n=25) 98.6 (n=12) 99.6 (n=5) 99.8 (n=6) 99.8 (n=0) 100.0 (n=1)

41. Application (Continued) Blood Glucose Level (mg/100 ml) True Diabetics (%)True Nondiabetics (%) All over 110mg/100 ml are classified as diabetics (True positives) (False positives) All under 110mg/100 ml are classified as non-diabetics (False Negatives)(True negatives) Totals100.0

42. Application (Continued) §Sensitivity = §Specificity =

43. Predictive Values §Determines relationship between sensitivity, specificity, and prevalence §When prevalence is low, even a highly specific test will give a relatively large number of false positives because of the many nondiseased persons being tested.

44. Positive Predictive Value §Likelihood that an individual with a positive test has the disease §TP/TP+FP

45. Negative Predictive Value §Likelihood that an individual with a negative test does not have the disease §TN / TN + FN

46. Predictive Value of Diabetes Application §Positive Predictive Value = §Negative Predictive Value =

47. Considerations for Selection of Screens §Prevalence §Financial §Availability/ Feasibility of Treatment §Relative costs of classifying persons as FN and FP