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Epidemiology
Epidemiology
Epidemiology
Epidemiology
Epidemiology
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Epidemiology
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Epidemiology

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Epidemiology

Epidemiology

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  • 1. EPIDEMIOLOGY Crisbert I. Cualteros, M.D. http://crisbertcualteros.page.tl
  • 2. DEFINITION
    • Study of the distribution and determinants of health and disease among populations and the application of such study to the prevention and control of health problems.
    • Determination of the nature, extent and determinants of disease or health problems
    • among populations
  • 3. COMPONENTS OF EPIDEMIOLOGY
    • Descriptive Epidemiology
        • study of the distribution of disease
        • variables commonly examined are descriptive of person, place and time
    • Analytic Epidemiology
        • use of epidemiologic methods to explain disease occurrence or elucidate causal mechanisms
  • 4. CHARACTERISTICS / FEATURES OF EPIDEMIOLOGY
    • It is a quantitative science.
    • It is an applied science.
    • Its methods are generally observational.
    • Its focus is the group or community of persons.
    • Its methods are systematic and orderly.
  • 5. DESCRIPTIVE EPIDEMIOLOGY
    • I. Definition
        • study the amount and distribution of disease within a population
    • II . Uses
        • evaluate trends in health and make comparisons
        • health planning
        • identify problems to be studied by analytical methods = hypothesis
  • 6. DESCRIPTIVE EPIDEMIOLOGY
    • III. Community Reaction to Disease
        • Absence of disease
            • No cases on current record
            • Disease absent from the beginning or has been eradicated
        • Sporadic
            • Occurrence of few and unrelated cases
        • Endemic
            • Constant occurrence of disease
        • Epidemic
            • Occurrence of a number of cases of disease in excess of the normal expectancy
  • 7. DESCRIPTIVE EPIDEMIOLOGY
    • IV. Descriptive Variables
    • A. Person
    • 1. Age
            • Different diseases show different age patterns
      • Disease Characteristic Pattern of Magnitude
      • Confers long lasting immunity decreasing with age
      • Degenerative diseases or increasing with age
      • w/ long latency
      • Reflects low resistance high at extreme ages
      • of young and old
      • Reflects high exposure high in middle age groups
      • during middle age
  • 8. VARIABLES OF PERSON
    • 2. Sex
      • Difference in sexual constitutional, e.g. hormonal balance
      • Greater exposure of males due to habits,
      • recreation, occupation, lifestyle
      • Greater health consciousness of females:
        • Early consultation, diagnosis and treatment
        • Better compliance with treatment
        • More cases recorded – artifactual reason
  • 9. VARIABLES OF PERSON
    • 3. Civil Status
      • Differences in lifestyle that are causally related to particular diseases
      • Self-selection
      • Concordance between marital partners
      • Greater family support among the married
    • 4. Socio-economic class – affects state of nutrition,
    • level of health awareness or knowledge, etc
    • 5. Genetics
  • 10. DESCRIPTIVE VARIABLES
    • B. Place
    • 1. Variables Of Place
          • geographic divisions
          • physical environment
            • climate, altitude, soil, vegetation, fauna
            • biological environment: infectious disease agents, animal reservoirs, vectors
          • socio-cultural-political-economic environment
            • related to level of development
  • 11. VARIABLES OF PLACE
      • population characteristics
          • density
          • urban vs. rural
          • mobility
          • herd immunity
  • 12. PLACE
    • 2. Etiology of Disease Variations
      • Real Causes - reflect true increase in risk
        • deteriorating or improving environment
        • quality, availability and distribution of medical care
      • Artifactual Causes
        • reliability of diagnosis
        • completeness of reporting and recording of diseases, births and deaths
  • 13. DESCRIPTIVE VARIABLES
    • C. Time
      • Temporal variations – changes / fluctuations in disease frequency with the passage of time
      • 1. Types of Temporal Variations:
        • Secular Trends
        • Cyclic Fluctuations
        • Short-term Irregular – e.g. Epidemics / outbreaks
  • 14. TEMPORAL VARIATIONS
    • Secular Trend Cyclic Fluctuations
    • Measure of frequency Mortality rates Incidence Rates
    • Nature of change Increase or Almost regular rises
    • decrease
    • Period of observation 10 years or hours, days, weeks,
    • longer months, years (≤5)
    • Type of Disease Chronic Acute
  • 15. TIME
    • 2. Reasons for Changes in Mortality Rates
      • Artifactual or non-etiologic
        • Error in the numerator
          • guess diagnosis / misdiagnosis
          • inaccurate counting
          • change in the International Classification of Diseases
        • Error in the denominator
          • over or underestimate of the population
  • 16. TIME
    • Change in Case Fatality Rate, w/o change in Incidence Rate
        • change in availability or utilization of health care services
        • change in treatment modalities
        • change in risk to superimposed infections
  • 17. TIME
    • Change in Incidence Rate, w/o change in Case Fatality Rate
        • Artifactual or non-etiologic
        • Real or etiologic
          • change in disease agent
          • change in herd resistance
          • change in the environment
  • 18. TIME
    • 3. Types of Cyclic Fluctuations
        • Cyclic Intrinsic Fluctuation
            • change/s in the host
            • change in herd resistance
            • accumulation of susceptibles
        • Cyclic Extrinsic Fluctuation (seasonal variation)
            • change in the environment
            • change in the disease agent
  • 19. Analytic Epidemiology
    • Definition
        • study the determinants of disease or reasons for low and high frequency in specific groups
        • employs Epidemiologic Methods :
            • Definition of the problem
            • Appraisal of existing facts
            • Formulation of hypothesis
            • Testing of hypothesis
            • Conclusion and practical application
  • 20. ANALYTIC EPIDEMIOLOGY
    • II. Principal Uses
        • Community diagnosis
        • Investigation of epidemics
        • Determination of disease etiology
        • Evaluation of community intervention and programs
  • 21. COMMUNITY DIAGNOSIS
    • Definition of the Problem
          • Determining the extent and magnitude of the problem using statistical indices
          • Comparison of the statistical indices with those of other places and other diseases
          • computation of economic burden of disease: cost of losses due to disability, death, treatment and prevention
  • 22. COMMUNITY DIAGNOSIS
    • II. Appraisal of Existing Facts
          • Determining the:
            • state of knowledge of disease or health problem etiology
            • distribution of the disease/ problem in terms of person, place and time
            • factors associated with the disease/ problem
  • 23. COMMUNITY DIAGNOSIS
    • III. Formulation of Hypothesis
        • Explanations for the existence and magnitude of the disease / problem
    • IV. Testing of Hypothesis
    • V. Conclusion and Practical Solutions to the
    • Problem
  • 24. EPIDEMICS
    • Definition
        • the occurrence of any number of cases of a disease clearly in excess of the normal expectancy or what usually prevails
  • 25. EPIDEMICS
    • II. Causes of Epidemics
      • flare up of an old or existing disease
        • increased virulence of existing strain
        • introduction of a new strain of the existing agent
        • increased capacity to multiply
        • decreased resistance of the population
        • dilution of herd resistance with a susceptible population
        • changes in the environment favoring disease transmission, e.g. calamities destroying health facilities, factors favoring survival and multiplication of vectors, changes in climate, temperature, etc.
  • 26. Causes of Epidemics
    • new disease
        • introduction of a disease not previously present in the community
        • disease previously affecting lower animals affecting man for the first time
        • recognition for the first time of previously occurring disease known by another name
  • 27. EPIDEMICS
    • III. Classification of Epidemics according to:
    • 1. Onset (of epidemic)
            • explosive , abrupt, sudden – majority of cases occurring within one incubation period
            • staggering , insidious, gradual
          • 2. Exposure (of cases)
            • mass or simultaneous – exposure occurred about the same time
            • progressive – cases were exposed one after the other from a primary case
  • 28. CLASSIFICATION OF EPIDEMICS
    • 3. Transmission
      • common vehicle – single or multiple exposure
      • propagated
          • contact-transmitted: person to person
          • vector-transmitted
  • 29. CLASSIFICATION OF EPIDEMICS
    • 4. Epidemic Curve
      • classical – short ascending, long descending limbs; water-borne
      • inverted – long ascending, short descending limbs; vector-borne
  • 30. Epidemic Curve
    • bell-shaped – ascending and descending limbs about equal, peak is rounded; contact-transmitted
    • point - ascending and descending limbs about equal, peak is pointed; food poisoning
  • 31. EPIDEMICS
    • IV. Termination of Epidemics
        • eradication / killing of disease agents at the source or reservoirs
        • interruption or closure of transmission
        • exhaustion of susceptibles
  • 32. EPIDEMICS
    • V. Steps in the Investigation of Epidemics
    • 1. Definition of the problem
            • verify the diagnosis
            • establish existence of an epidemic
      • 2. Appraisal of existing facts
            • characterize the distribution of cases by person, place and time
  • 33. INVESTIGATION OF EPIDEMICS
    • 3. Formulation of hypothesis
      • as to source of infection, mode of transmission, factors that may have given rise to the epidemic
    • 4. Testing of hypothesis
        • conduct an epidemiological investigation (case control)
    • 5. Conclusion and recommendations for control
    • and prevention
  • 34. DETERMINATION OF DISEASE ETIOLOGY
    • I. Types of Epidemiologic Studies
    • A. Descriptive Studies
    • 1. Uses
            • determination of distribution of disease according to person, place and time
            • delineation of syndrome as a disease entity
            • establishment of the natural history of disease
            • classification of disease
          • manifestational: pathologic and symptomatic
            • experiential: based on similarity of experience
  • 35. Descriptive Studies
    • 2. Types
        • Case report
            • unit of study: single person with a disease
            • limitation: based on experience of a single person
            • provides first clues in the identification of a disease or adverse effects of exposure
  • 36. TYPES OF DESCRIPTIVE STUDIES
    • Case series
        • unit of study: group of persons with a similar disease
        • Uses:
          • formulation of criteria for diagnosis
          • formulation of indications for treatment
          • identification of prognostic factors
          • determination of survival rates
  • 37. CASE SERIES
    • Limitation
      • limited generalizability because of unrepresentativeness of subjects and absence of comparison group
  • 38. TYPES OF DESCRIPTIVE STUDIES
    • Prevalence/Cross-sectional/ Surveys
        • measures prevalence of disease or an event
        • information about exposure and outcome are obtained simultaneously in a well-defined population
  • 39. PREVALENCE/CROSS-SECTIONAL/ SURVEYS
    • Uses
      • determination of prevalence of risk factors
      • determination of frequency of prevalent
      • cases
      • determination of health status and health
      • needs
      • formulation of hypothesis
  • 40. PREVALENCE/CROSS-SECTIONAL/ SURVEYS
    • Advantages
      • quick and easy to perform
    • Disadvantages
      • temporality cannot be ascertained
      • selects for longer-lasting and indolent cases
  • 41. TYPES OF DESCRIPTIVE STUDIES
    • Ecological Studies
      • crude way of exploring relationship between environment or occupation and disease
      • unit of study: populations or groups of people rather than individuals
      • hypothesis generating rather than hypothesis testing
  • 42. ECOLOGICAL STUDIES
    • Advantage
      • simple to conduct
    • Disdavantage
      • individual link between exposure and effect cannot be made (ecologic fallacy)
  • 43. Types of Epidemiologic Studies
    • B. Analytic Studies
    • Use
        • to determine whether a factor is causally associated with disease
        • to test epidemiologic hypotheses
    • 2. Categories
        • observational/ non-experimental
            • observes natural course of events
            • case control study, cohort study, cross-sectional study
  • 44. CATEGORIES OF ANALYTIC STUDIES
    • Experimental/ Interventional
      • exposure to the factor or treatment under study controlled by investigator
      • randomized clinical trial (rct), community trial, laboratory trial
  • 45. ANALYTIC STUDIES
    • 3. Types
      • Case-control Studies
        • cases (with disease) and controls (no disease) are selected from a chosen population
        • both are questioned or records are reviewed about presence or absence of a suspected cause/risk factor in the past
  • 46. CASE-CONTROL STUDIES
    • 1. Uses
      • to test risk factors
      • preferred if disease is rare
      • preferred if several factors are associated with disease of interest
  • 47. CASE-CONTROL STUDIES
    • 2. Requirements for valid results
      • Cases must be representative of all those with disease and clearly defined.
      • Controls must be representative of all those without the disease and come from same community or source as the cases .
  • 48. CASE-CONTROL STUDIES
    • 3. Analysis
      • Odd’s Ratio (OR)
        • proportion of those with history of exposure to the factor among the cases (a/a+c) is compared to those with history of exposure (b/b+d) to the factor among the controls
        • OR = ad/bc
  • 49. ANALYSIS OF CASE CONTROL STUDIES
            • Outcome (Disease)
    • + -
    • + a b
    • Exposure
    • (Factor)
    • - c d
    • a+c b+d
    • * statistical association between factor and outcome
    • exists if (a/a+c) ≠ (b/b+d)
    • * association is probably causal , if OR > 1
  • 50. CASE-CONTROL STUDIES
    • 4. Advantages
      • more economical
      • smaller sample size required
      • suitable for rare diseases
      • suitable for diseases associated with multiple exposures
  • 51. CASE-CONTROL STUDIES
    • 5. Disadvantages
        • more susceptible to bias of recall
        • estimate of risk is indirect
        • controls more difficult to assemble
        • temporal relationship between factor and outcome cannot be ascertained
  • 52. TYPES OF ANALYTIC STUDIES
    • Cohort Studies
        • groups of subjects are chosen on the basis of having been exposed to a factor or not
        • groups are followed up to identify those who develop the disease or outcome
  • 53. COHORT STUDIES
    • Uses
        • to test prognostic factors
        • to directly measure risk of development of disease or outcome
        • provide more definitive information about disease etiology
        • preferred for study of rare exposures
  • 54. COHORT STUDIES
    • 2. Requirement for valid results
      • Similarity of comparison groups
    • 3. Types
        • concurrent
          • Subjects are free of disease or outcome of interest at the time of initiation of the study.
          • Investigator follows-up the groups or cohorts from exposure to appearance of disease or outcome.
  • 55. TYPES OF COHORT STUDIES
    • . Non-concurrent
        • Subjects who are free of the disease or outcome of interest at some point in the past are identified in terms of their exposure level.
        • Disease or outcome status is determined through existing records.
        • At the time the study is conducted, the specified follow-up period has elapsed.
  • 56. COHORT STUDIES
    • 4. Analysis
      • Relative Risk or Risk Ratio(RR)
        • proportion of subjects with the disease or outcome among the exposed (a/a+b) is compared to proportion of subjects with the disease or outcome among the unexposed (c/c+d)
        • RR = a/a+b ÷ c/c+d
  • 57. ANALYSIS OF COHORT STUDIES
            • Outcome (Disease)
    • + -
    • + a b
    • Exposure
    • (Factor)
    • - c d
    • a+c b+d
    • * statistical association between factor and outcome
    • exists if (a/a+b) ≠ (c/c+d)
    • * association is probably causal , if RR > 1
  • 58. ANALYSIS OF COHORT STUDIES
    • Attributable Risk (AR)
      • estimate of the amount of risk that is attributable to the risk factor
      • AR = a/(a+b) - c/(c+d)
  • 59. COHORT STUDIES
    • 5. Advantages
        • provides direct estimate of risk
        • temporality can be ascertained (for concurrent
    • studies)
        • less biases of recall and observation
        • allows for determination of population-based rates
        • controls easier to assemble
        • variations in exposure can be followed-up
        • unsuspected effects of the exposure may be observed
  • 60. COHORT STUDIES
    • 6. Disadvantages
        • more expensive
        • follow-up period may be long
        • high attrition rate
        • large sample size required
        • change in exposure rates over long periods of time
  • 61. COMPARISON OF CHARACTERISTICS OF CASE CONTROL AND COHORT STUDIES
    • Case Control Cohort
    • Starting population diseased group exposed group
    • Control Group non-diseased unexposed
    • Information Sought frequency of disease rate
    • exposure to
    • risk factor
    • Principal bias knowledge of knowledge of
    • disease influences exposure influences
    • report of exposure diagnosis
  • 62. COMPARISON OF CHARACTERISTICS OF CASE CONTROL AND COHORT STUDIES
    • Case Control Cohort
    • Time to Complete short usually long
    • Study
    • Measure of Odd’s Ratio Relative Risk
    • Association
  • 63. TYPES OF ANALYTIC STUDIES
    • Experimental Studies
      • Requirement for validity: complete comparability of comparison groups
        • 1. Types
          • Clinical Trial - Randomized Controlled Trial (RCT)
            • investigator randomly places the subjects to one of the intervention groups
            • ex. drug or surgical trials
            • used if strong evidence for association already exists
  • 64. TYPES OF EXPERIMENTAL STUDIES
    • Field or community trials
      • subjects are people in the general population
    • who are disease-free but are presumed to be
    • at risk
      • ex. trials of preventive measures, e.g.
    • immunization
  • 65. FIELD OR COMMUNITY TRIALS
    • Requirements
      • high incidence of disease under study
      • availability of facilities for observation
      • accessibility of subjects
      • availability of resources for precise diagnosis
      • and follow-up
  • 66. EXPERIMENTAL STUDIES
    • 2. Analysis
      • comparison of disease or outcome rate in
    • experimental (P 1 ) = (a/a+c) and control
    • groups (P 2 ) = (b/b+d)
  • 67. ANALYSIS OF EXPERIMENTAL STUDIES
    • Therapeutic / Preventive
    • Measure + -
    • + a b
    • Disease/
    • Outcome - c d
    • a+c b+d
  • 68. ANALYSIS OF EXPERIMENTAL STUDIES
    • Protective Value = P 2 – P 1
    • P 2
  • 69. EXPERIMENTAL STUDIES
    • 3. Advantage
      • Provide the strongest evidence for testing hypothesis
    • 4. Limitation
      • ethical issues, especially for clinical trials
  • 70. Determination of Disease Etiology
    • II. Assessment of Results
      • 1. determine if statistical association between factor and outcome occurs
      • 2. if association exists, determine if due to:
        • chance
          • perform significance testing
        • extraneous or confounding variables
          • matching
          • specification or restriction
          • standardization of rates
          • stratified analysis
  • 71. Assessment of Results
    • if association exists, determine if due to:
      • causal relationship
        • criteria:
            • 1. measures of strength of association – OR, RR, Protective Value
            • 2. temporality – exposure occurred prior to outcome
            • 3. dose-response relationship
  • 72. CRITERIA FOR CAUSAL ASSOCIATION
    • 4. specificity – factor associated with only 1 or
    • limited number of diseases
    • 5. consistency of association – distribution of factor and disease is similar in different
    • sub-groups
    • 6. biologic plausibility – consistency with existing knowledge

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