EPIDEMIOLOGY Crisbert I. Cualteros, M.D. http://crisbertcualteros.page.tl
DEFINITION <ul><li>Study of the  distribution  and  determinants  of health and disease among  populations  and the applic...
COMPONENTS OF EPIDEMIOLOGY <ul><li>Descriptive Epidemiology </li></ul><ul><ul><ul><li>study of the distribution of disease...
CHARACTERISTICS / FEATURES OF EPIDEMIOLOGY <ul><li>It is a quantitative science. </li></ul><ul><li>It is an applied scienc...
DESCRIPTIVE EPIDEMIOLOGY <ul><li>I.  Definition </li></ul><ul><ul><ul><li>study the  amount  and  distribution  of disease...
DESCRIPTIVE EPIDEMIOLOGY <ul><li>III. Community Reaction to Disease </li></ul><ul><ul><ul><li>Absence of disease   </li></...
DESCRIPTIVE EPIDEMIOLOGY <ul><li>IV. Descriptive Variables </li></ul><ul><li>A. Person </li></ul><ul><li>1.   Age </li></u...
VARIABLES OF PERSON <ul><li>2. Sex </li></ul><ul><ul><li>Difference in sexual constitutional, e.g. hormonal balance </li><...
VARIABLES OF PERSON <ul><li>3. Civil Status </li></ul><ul><ul><li>Differences in lifestyle that are causally related to pa...
DESCRIPTIVE VARIABLES <ul><li>B. Place </li></ul><ul><li>1. Variables Of Place </li></ul><ul><ul><ul><ul><li>geographic di...
VARIABLES OF PLACE <ul><ul><li>population characteristics </li></ul></ul><ul><ul><ul><ul><li>density </li></ul></ul></ul><...
PLACE <ul><li>2. Etiology of Disease Variations </li></ul><ul><ul><li>Real Causes - reflect true increase in risk   </li><...
DESCRIPTIVE VARIABLES <ul><li>C. Time </li></ul><ul><ul><li>Temporal variations –  changes / fluctuations in disease frequ...
TEMPORAL VARIATIONS <ul><li>Secular Trend   Cyclic Fluctuations </li></ul><ul><li>Measure of frequency   Mortality rates  ...
TIME <ul><li>2. Reasons for Changes in Mortality Rates </li></ul><ul><ul><li>Artifactual or non-etiologic </li></ul></ul><...
TIME <ul><li>Change in Case Fatality Rate, w/o change in Incidence Rate </li></ul><ul><ul><ul><li>change in availability o...
TIME <ul><li>Change in Incidence Rate, w/o change in Case Fatality Rate </li></ul><ul><ul><ul><li>Artifactual or non-etiol...
TIME <ul><li>3. Types of Cyclic Fluctuations </li></ul><ul><ul><ul><li>Cyclic Intrinsic Fluctuation </li></ul></ul></ul><u...
Analytic Epidemiology   <ul><li>Definition </li></ul><ul><ul><ul><li>study the  determinants  of disease or  reasons  for ...
ANALYTIC EPIDEMIOLOGY <ul><li>II. Principal Uses </li></ul><ul><ul><ul><li>Community diagnosis </li></ul></ul></ul><ul><ul...
COMMUNITY DIAGNOSIS <ul><li>Definition of the Problem </li></ul><ul><ul><ul><ul><li>Determining the extent and magnitude o...
COMMUNITY DIAGNOSIS <ul><li>II.  Appraisal of Existing Facts </li></ul><ul><ul><ul><ul><li>Determining the: </li></ul></ul...
COMMUNITY DIAGNOSIS <ul><li>III.   Formulation of Hypothesis </li></ul><ul><ul><ul><li>Explanations for the existence and ...
EPIDEMICS <ul><li>Definition </li></ul><ul><ul><ul><li>the occurrence of  any number of cases  of a disease clearly  in ex...
EPIDEMICS <ul><li>II. Causes of Epidemics </li></ul><ul><ul><li>flare up of an old or existing disease </li></ul></ul><ul>...
Causes of Epidemics <ul><li>new disease </li></ul><ul><ul><ul><li>introduction of a disease not previously present in the ...
EPIDEMICS <ul><li>III. Classification of Epidemics according to: </li></ul><ul><li>1. Onset (of epidemic) </li></ul><ul><u...
CLASSIFICATION OF EPIDEMICS <ul><li>3. Transmission </li></ul><ul><ul><li>common vehicle – single or multiple exposure </l...
CLASSIFICATION OF EPIDEMICS <ul><li>4. Epidemic Curve </li></ul><ul><ul><li>classical – short ascending, long descending l...
Epidemic Curve <ul><li>bell-shaped – ascending and descending limbs about equal, peak is rounded; contact-transmitted </li...
EPIDEMICS <ul><li>IV. Termination of Epidemics </li></ul><ul><ul><ul><li>eradication / killing of disease agents at the so...
EPIDEMICS <ul><li>V. Steps in the Investigation of Epidemics   </li></ul><ul><li>1. Definition of the problem </li></ul><u...
INVESTIGATION OF EPIDEMICS <ul><li>3. Formulation of hypothesis </li></ul><ul><ul><li>as to source of infection, mode of t...
DETERMINATION OF DISEASE ETIOLOGY <ul><li>I. Types of Epidemiologic Studies </li></ul><ul><li>A. Descriptive Studies </li>...
Descriptive Studies <ul><li>2. Types </li></ul><ul><ul><ul><li>Case report </li></ul></ul></ul><ul><ul><ul><ul><ul><li>uni...
TYPES OF DESCRIPTIVE STUDIES <ul><li>Case series </li></ul><ul><ul><ul><li>unit of study: group of persons with a similar ...
CASE SERIES <ul><li>Limitation </li></ul><ul><ul><li>limited generalizability because of unrepresentativeness of subjects ...
TYPES OF DESCRIPTIVE STUDIES <ul><li>Prevalence/Cross-sectional/ Surveys </li></ul><ul><ul><ul><li>measures prevalence of ...
PREVALENCE/CROSS-SECTIONAL/ SURVEYS <ul><li>Uses </li></ul><ul><ul><li>determination of prevalence of risk factors </li></...
PREVALENCE/CROSS-SECTIONAL/ SURVEYS <ul><li>Advantages </li></ul><ul><ul><li>quick and easy to perform </li></ul></ul><ul>...
TYPES OF DESCRIPTIVE STUDIES <ul><li>Ecological Studies </li></ul><ul><ul><li>crude way of exploring relationship between ...
ECOLOGICAL STUDIES <ul><li>Advantage </li></ul><ul><ul><li>simple to conduct </li></ul></ul><ul><li>Disdavantage </li></ul...
Types of Epidemiologic Studies <ul><li>B. Analytic Studies </li></ul><ul><li>Use </li></ul><ul><ul><ul><li>to determine wh...
CATEGORIES OF ANALYTIC STUDIES <ul><li>Experimental/ Interventional </li></ul><ul><ul><li>exposure to the factor or treatm...
ANALYTIC STUDIES <ul><li>3. Types </li></ul><ul><ul><li>Case-control Studies </li></ul></ul><ul><ul><ul><li>cases (with di...
CASE-CONTROL STUDIES <ul><li>1. Uses </li></ul><ul><ul><li>to test risk factors   </li></ul></ul><ul><ul><li>preferred if ...
CASE-CONTROL STUDIES <ul><li>2. Requirements for valid results </li></ul><ul><ul><li>Cases must be representative of all t...
CASE-CONTROL STUDIES <ul><li>3. Analysis </li></ul><ul><ul><li>Odd’s Ratio (OR) </li></ul></ul><ul><ul><ul><li>proportion ...
ANALYSIS OF CASE CONTROL STUDIES <ul><ul><ul><ul><ul><li>Outcome (Disease) </li></ul></ul></ul></ul></ul><ul><li>  +   - <...
CASE-CONTROL STUDIES <ul><li>4. Advantages </li></ul><ul><ul><li>more economical  </li></ul></ul><ul><ul><li>smaller sampl...
CASE-CONTROL STUDIES <ul><li>5. Disadvantages </li></ul><ul><ul><ul><li>more susceptible to bias of recall </li></ul></ul>...
TYPES OF ANALYTIC STUDIES <ul><li>Cohort Studies </li></ul><ul><ul><ul><li>groups of subjects are chosen on the basis of h...
COHORT STUDIES <ul><li>Uses </li></ul><ul><ul><ul><li>to  test prognostic factors </li></ul></ul></ul><ul><ul><ul><li>to d...
COHORT STUDIES <ul><li>2. Requirement for valid results </li></ul><ul><ul><li>Similarity of comparison groups </li></ul></...
TYPES OF COHORT STUDIES <ul><li>.  Non-concurrent </li></ul><ul><ul><ul><li>Subjects who are free of the disease or outcom...
COHORT STUDIES <ul><li>4. Analysis </li></ul><ul><ul><li>Relative Risk or Risk Ratio(RR) </li></ul></ul><ul><ul><ul><li>pr...
ANALYSIS OF COHORT STUDIES <ul><ul><ul><ul><ul><li>Outcome (Disease) </li></ul></ul></ul></ul></ul><ul><li>  +   - </li></...
ANALYSIS OF COHORT STUDIES <ul><li>Attributable Risk (AR) </li></ul><ul><ul><li>estimate of the amount of risk that is att...
COHORT STUDIES <ul><li>5. Advantages </li></ul><ul><ul><ul><li>provides direct estimate of risk </li></ul></ul></ul><ul><u...
COHORT STUDIES <ul><li>6. Disadvantages </li></ul><ul><ul><ul><li>more expensive </li></ul></ul></ul><ul><ul><ul><li>follo...
COMPARISON OF CHARACTERISTICS OF CASE CONTROL AND COHORT STUDIES <ul><li>  Case Control   Cohort </li></ul><ul><li>Startin...
COMPARISON OF CHARACTERISTICS OF CASE CONTROL AND COHORT STUDIES <ul><li>  Case Control   Cohort </li></ul><ul><li>Time to...
TYPES OF ANALYTIC STUDIES <ul><li>Experimental Studies </li></ul><ul><ul><li>Requirement for validity: complete comparabil...
TYPES OF EXPERIMENTAL STUDIES <ul><li>Field or community trials </li></ul><ul><ul><li>subjects are people in the general p...
FIELD OR COMMUNITY TRIALS <ul><li>Requirements </li></ul><ul><ul><li>high incidence of disease under study </li></ul></ul>...
EXPERIMENTAL STUDIES <ul><li>2. Analysis </li></ul><ul><ul><li>comparison of disease or outcome rate in  </li></ul></ul><u...
ANALYSIS OF EXPERIMENTAL STUDIES <ul><li>Therapeutic / Preventive </li></ul><ul><li>  Measure    +   - </li></ul><ul><li> ...
ANALYSIS OF EXPERIMENTAL STUDIES <ul><li>Protective Value = P 2  – P 1 </li></ul><ul><li>  P 2 </li></ul>
EXPERIMENTAL STUDIES <ul><li>3. Advantage </li></ul><ul><ul><li>Provide the strongest evidence for testing hypothesis </li...
Determination of Disease Etiology <ul><li>II. Assessment of Results </li></ul><ul><ul><li>1. determine if statistical asso...
Assessment of Results <ul><li>if association exists, determine if due to:   </li></ul><ul><ul><li>causal relationship </li...
CRITERIA FOR CAUSAL ASSOCIATION <ul><li>4. specificity – factor associated with only 1 or  </li></ul><ul><li>limited numbe...
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Epidemiology

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Epidemiology

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Epidemiology

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

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