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Epidemiology: Challenges and Answers in the Context of Globalization

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Epidemiology: Challenges and Answers in the Context of Globalization

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  1. Epidemiology: Challenges and Answers in the Context of Globalization Moyses Szklo Professor of Epidemiology and Medicine The Johns Hopkins Bloomberg School of Public Health and School of Medicine

  2. Genetic Epidemiology • Resurgence of Social Epidemiology

  3. Genetic Epidemiology • Resurgence of Social Epidemiology *Relevant to Public Health

  4. Genetic Epidemiology • Resurgence of Social Epidemiology *Relevant to Public Health

  5. Genetic Epidemiology • Resurgence of Social Epidemiology *Relevant to Public Health

  6. Host Increase the host’s resistance to the agent (e.g., vaccination) Kill the agent and/or the vector (e.g., use of pesticides, prophylactic anti-Tb therapy) Render the environment hostile to the agent’s or the vector’s growth (e.g., eliminate poverty, store food in cold temperatures) Primary Prevention Strategies Vector Agent Environment THE EPIDEMIOLOGIC TRIAD: AGENT, HOST AND ENVIRONMENT

  7. Genetic Epidemiology • Resurgence of Social Epidemiology *Relevant to Public Health

  8. Detection based on symptoms or signs occurring at the beginning of the clinical phase Delayed detection Detection based on symptoms and signs after the beginning of the clinical phase Onset of exposure to risk factor(s) -or- -or- Biologic onset of disease PRIMARY PREVENTION SECONDARY PREVENTION TERTIARY PREVENTION Level of effectiveness TIME NATURAL HISTORY Early Detection (if possible) TIME

  9. Genetic Epidemiology • Resurgence of Social Epidemiology *Relevant to Public Health

  10. Causal Components and Sufficient Causes* of Stroke: Hypothetical Causality Chain *Sufficient cause: a set of minimal conditions and events that inevitably produce disease (Rothman K. Modern Epidemiology. Boston, Toronto: Little Brown and Company,1986)

  11. High Salt Intake Obesity Arterial Hypertension Low Levels of Physical Activity Stress Stroke Genetic Susceptibility Intermediate Sufficient Cause Proximal Sufficient Cause STROKE PREVENTION Population-wide strategy:  per capita salt intake= 33% stroke incidence ~ 22% (Law MR, et al. Br Med J 1991;302:819-24) “In order to implement preventive measures, it is not necessary to understand the causal mechanisms in their entirety” (MacMahon B, Pugh TF, Ipsen J. Epidemiology: Principles and Methods. Boston: Little, Brown and Co., 1960, p. 18) Poor access to healthy foods Low Social Class Excessive salt content of processed foods Distal Sufficient Cause

  12. Poor access to healthy foods Low Social Class Arterial Hypertension Excessive salt content of processed foods Stroke Stroke Genetic Susceptibility Distal Sufficient Cause Proximal Sufficient Cause STROKE PREVENTION No. of individuals Systolic Blood Pressure High Salt Intake Obesity Low Levels of Physical Activity Stress Intermediate Sufficient Cause

  13. Poor access to healthy foods Low Social Class High Salt Intake Obesity Arterial Hypertension Low Levels of Physical Activity Excessive salt content of processed foods Stress Stroke Genetic Susceptibility Distal Sufficient Cause Intermediate Sufficient Cause Proximal Sufficient Cause STROKE PREVENTION High risk strategy: identification, treatment and control of all patients with hypertension   stroke incidence ~ 15% (Law MR, et al. Br Med J 1991;302:819-24) BP levels with high RR, low ARPOP No. of individuals Systolic Blood Pressure

  14. Poor access to healthy foods Low Social Class High Salt Intake Obesity Arterial Hypertension Low Levels of Physical Activity Excessive salt content of processed foods Stress Stroke Genetic Susceptibility Distal Sufficient Cause Intermediate Sufficient Cause Proximal Sufficient Cause STROKE PREVENTION Blood pressure levels with low RR and high ARPOP High risk strategy: identification, treatment and control of all patients with hypertension   stroke incidence ~ 15% (Law MR, et al. Br Med J 1991;302:819-24) BP levels with high RR, low ARPOP No. of individuals Systolic Blood Pressure

  15. Poor access to healthy foods Low Social Class High Salt Intake Obesity Arterial Hypertension Low Levels of Physical Activity Excessive salt content of processed foods Stress Stroke Genetic Susceptibility Distal Sufficient Cause Intermediate Sufficient Cause Proximal Sufficient Cause STROKE PREVENTION Risk of Stroke Systolic Blood Pressure

  16. Poor access to healthy foods Low Social Class High Salt Intake Obesity Arterial Hypertension Low Levels of Physical Activity Excessive salt content of processed foods Stress Stroke Genetic Susceptibility Distal Sufficient Cause Intermediate Sufficient Cause Proximal Sufficient Cause STROKE PREVENTION Population-wide strategy:  per capita salt intake= 33% stroke incidence ~ 22% (Law MR, et al. Br Med J 1991;302:819-24) Blood pressure levels with low RR and high ARPOP BP levels with high RR, low ARPOP No. of individuals Systolic Blood Pressure

  17. Poor access to healthy foods Low Social Class High Salt Intake Obesity Arterial Hypertension Low Levels of Physical Activity Excessive salt content of processed foods Stress Stroke Genetic Susceptibility Distal Sufficient Cause Intermediate Sufficient Cause Proximal Sufficient Cause STROKE PREVENTION Population-wide strategy:  per capita salt intake= 33% stroke incidence ~ 22% (Law MR, et al. Br Med J 1991;302:819-24) Blood pressure levels with low RR and high ARPOP BP levels  high RR, low ARPOP No. of individuals Systolic Blood Pressure

  18. High Salt Intake Obesity Arterial Hypertension Low Levels of Physical Activity Stress Stroke Genetic Susceptibility Intermediate Sufficient Cause Proximal Sufficient Cause STROKE PREVENTION Population-wide strategy:  per capita salt intake= 33% stroke incidence ~ 22% (Law MR, et al. Br Med J 1991;302:819-24) (Rose G, Int J Epidemiol 1985;14:32-38) No. of individuals Kenia nomads Civil servants Systolic Blood Pressure Poor access to healthy foods Low Social Class Excessive salt content of processed foods Distal Sufficient Cause

  19. BRCA1 Breast cancer - often early age at onset (50%-85%) Second primary breast cancer (40%-60%) BRCA2 ovarian cancer (15%-45%) male breast cancer (6%) breast cancer (50%-85%) Possible increased risk of other cancers (eg, prostate, colon) ovarian cancer (10%-20%) Increased risk of prostate, laryngeal, and pancreatic cancers (magnitude unknown) Life Time Associated Risks of Cancer

  20. How Much Breast and Ovarian Cancer Is Hereditary? 15%-20% 5%–10% 5%–10% Breast Cancer Ovarian Cancer Sporadic Hereditary GENETIC INHERITANCE: - High Relative Risk - Low Population Attributable Risk

  21. False Negatives True Positives 278 128 150 10 140 150 1st Phase: Sensitivity of Family History = 0.54* 2nd Phase: Sensitivity of Mammography = 0.93** High Risk Screening  Program Sensitivity= 0.54 × 0.93 = 0.50 • SENSITIVITY OF A HIGH RISK SCREENING PROGRAM FOR INCIDENT BREAST CANCER CASES DURING ONE YEAR IN A TARGET POPULATION OF 100 000 WOMEN¶ • Average yearly incidence in S. Paulo, 1998-2000  278/100 000§ 1st Phase: Sensitivity of Family History of Breast Cancer = 0.54*; 2nd Phase: Sensitivity of Mammography = 0.93** §Câncer no Brasil- Dados do Registro de Câncer de Base Populacional. Disponível em http://www.inca.gov.br/vigilancia/ CONPREV-INCA-MS e IBGE-MP ¶Szklo M. J Gen Intern Med 1990; 5(Suppl):S47-S49 *Hartmann et al, New Eng J Med 2005;353:229-37 **Mushlin et al, Am J Prev Med 1998;14:143-53

  22. False Negatives True Positives 278 278 128 20 170 150 10 140 150 258 Total Target Population-Wide Screening: Sensitivity of Mammography= 0.93 1st Phase: Sensitivity of Family History = 0.54* 2nd Phase: Sensitivity of Mammography = 0.93** High Risk Screening  Program Sensitivity= 0.54 × 0.93 = 0.50 • SENSITIVITY OF A HIGH RISK SCREENING PROGRAM FOR INCIDENT BREAST CANCER CASES DURING ONE YEAR IN A TARGET POPULATION OF 100 000 WOMEN¶ • Average yearly incidence in S. Paulo, 1998-2000  278/100 000§ 1st Phase: Sensitivity of Family History of Breast Cancer = 0.54*; 2nd Phase: Sensitivity of Mammography = 0.93** Total No. of False Negatives at the End of the 2nd Phase= 128 + 10= 138 §Câncer no Brasil- Dados do Registro de Câncer de Base Populacional. Disponível em http://www.inca.gov.br/vigilancia/ CONPREV-INCA-MS e IBGE-MP ¶Szklo M. J Gen Intern Med 1990; 5(Suppl):S47-S49 *Hartmann et al, New Eng J Med 2005;353:229-37 **Mushlin et al, Am J Prev Med 1998;14:143-53

  23. Use of Genetic Epidemiology in Public Health • Identification of genotypes that are effect modifiers: equivalent to selective screening – two steps: (1) identification of susceptibility gene, and (2) prevention or cessation of risk factor in those with the gene. • Possible negative consequence: shifts the responsibility of prevention to the individual [“Genetic Epidemiology: the epidemiology of the individual” (Wynder, personal communication)]. • Advantages: study of disease mechanisms, pharmacogenetics, vector resistance, etc.

  24. ONE OF THE MAIN FOUNDATIONS OF THE POPULATION-WIDE PREVENTION STRATEGY: SOCIAL EPIDEMIOLOGY

  25. Excessive salt content of processed foods High crime rate High Salt Intake Absence of supermarkets selling healthy foods Obesity Arterial Hypertension Low Levels of Physical Activity Stress Stroke Distal Sufficient Cause of the Intermediate Cause Genetic Susceptibility Intermediate Sufficient Cause GROUP LEVEL Example: reduction of salt content in processed foods Proximal Sufficient Cause STROKE PREVENTION INDIVIDUAL LEVEL INDIVIDUAL LEVEL

  26. INCIDENCE OF CORONARY EVENTS IN WHITES AND BLACKS, ARIC STUDY* (Diez Roux et al, New Engl J Med 2001;345:99-106) *Adjusted for center and age (5-year categories. CI, confidence interval Neighborhood groups correspond to 3 race-specific groups of neighborhoods defined according to summary socioeconomic scores. Group 1 (scores in the lower third): most disadvantaged neighborhood. Group 3 (highest third): most advantaged neighborhoods

  27. (J Epidemiol Community Health 2002;56:588-594)

  28. Genetic Epidemiology • Resurgence of Social Epidemiology *Relevant to Public Health

  29. Genetic Epidemiology • Resurgence of Social Epidemiology *Relevant to Public Health

  30. Examples of Epidemiologic Research Findings that Influenced Policy • Seatbelts • Active smoking • Indoor smoking (environmental tobacco smoking) • Salt content in baby foods • Disclosure of saturated fat content of food items • Radiation standards • Screening for cervical cancer

  31. Better Worse RULES OF EVIDENCE TO ASSESS THE EFFECTIVENESS OF A PREVENTIVE OR CURATIVE INTERVENTION OR PROGRAM ARE BASED ON EPIDEMIOLOGIC STUDY DESIGNS • LEVELS • META-ANALYSIS OF RANDOMIZED CLINICAL TRIALS WITH HOMOGENEITY • AT LEAST ONE RANDOMIZED CLINICAL TRIAL • TEMPORAL TREND DEMONSTRATING A DRAMATIC EFFECT OF THE INTERVENTION (“NATURAL EXPERIMENT”) – E.G., INSULIN IN DIABETES • META-ANALYSIS OF OBSERVATIONAL STUDIES WITH HOMOGENEITY • AT LEAST ONE OBSERVATIONAL STUDY (COHORT STUDIES ARE ASSIGNED A HIGHER LEVEL THAN CASE-CONTROL STUDIES) • QUASI-EXPERIMENTAL STUDIES • TEMPORAL TREND NOT SHOWING DRAMATIC EFFECT (WITHOUT CONTROLS) • CASE SERIES • EXPERT OPINION NOT BASED ON THE ABOVE STUDIES Based on: US Task Force on Preventive Services; Canadian Task Force on Periodic Health Examination Bigby M, Szklo M: Evidence-Based Dermatology. In : Fitzpatrick’, Dermatology in General Medicine (ed. By Freedberg IM et al). Vol. II; 2003: McGraw-Hill Medical Publishing Division, New York, pp. 2301-2311, 2003

  32. Better Worse RULES OF EVIDENCE TO ASSESS THE EFFECTIVENESS OF A PREVENTIVE OR CURATIVE INTERVENTION OR PROGRAM ARE BASED ON EPIDEMIOLOGIC STUDY DESIGNS • LEVELS • META-ANALYSIS OF RANDOMIZED CLINICAL TRIALS WITH HOMOGENEITY • AT LEAST ONE RANDOMIZED CLINICAL TRIAL • TEMPORAL TREND DEMONSTRATING A DRAMATIC EFFECT OF THE INTERVENTION (“NATURAL EXPERIMENT”) – E.G., INSULIN IN DIABETES • META-ANALYSIS OF OBSERVATIONAL STUDIES WITH HOMOGENEITY • AT LEAST ONE OBSERVATIONAL STUDY (COHORT STUDIES ARE ASSIGNED A HIGHER LEVEL THAN CASE-CONTROL STUDIES) • QUASI-EXPERIMENTAL STUDIES • TEMPORAL TREND NOT SHOWING DRAMATIC EFFECT (WITHOUT CONTROLS) • CASE SERIES • EXPERT OPINION NOT BASED ON THE ABOVE STUDIES Based on: US Task Force on Preventive Services; Canadian Task Force on Periodic Health Examination Bigby M, Szklo M: Evidence-Based Dermatology. In : Fitzpatrick’, Dermatology in General Medicine (ed. By Freedberg IM et al). Vol. II; 2003: McGraw-Hill Medical Publishing Division, New York, pp. 2301-2311, 2003

  33. PUBLICATION BIAS: SELECTION BIAS THAT OCCURS WHEN PUBLICATION OF A PAPER REPORTING FINDINGS OF A STUDY IS BASED ON FACTORS OTHER THAN THE QUALITY OF THE STUDY (Chan AW et al. Empirical evidence for selective reporting of outcomes in randomized trials: comparison of protocols to published articles. JAMA 2004;291:2457-65)

  34. Valid sample of studies BIASED sample of studies SAMPLING A “POPULATION” OF STUDIES: PUBLICATION BIAS Number of studies Total population of studies -60 -40 -20 0 20 40 60 Efficacy of an intervention (%)

  35. *p≤0.05 **p>0.05 105 RANDOMIZED TRIALS Identification of published RCTs approved for funding by the Canadian Institutes of Health Research from 1990-98 (Chan AW et al. CMAJ 2004;171:735-740)

  36. QUESTIONS: • IS PUBLICATION BIAS ENCOURAGED BY PEER REVIEWED JOURNALS? • PUBLICATION BIAS MAY BE THE RESULT OF THE JOURNAL’S EDITORIAL POLICY… • ARE AUTHORS AFRAID OF REJECTION OF “NEGATIVE” REPORTS?

  37. Factors Associated with the Odds of Publication: Multivariate Analysis (No. of studies= 285) (Easterbrook et al, 1991)

  38. Direction of findings in published trials by source of support (Davidson, 1986)

  39. ODDS RATIO= 3.8 (95% CI= 1.3, 11.3) Language Bias: Egger M, et al. Lancet. 1997;350:326–329. • Randomized trials published by German investigators in either German or English journals from 1985 through 1994 • No differences in quality between German- and English-written papers • Statistically significant results: • English-written papers: 63% • German-written papers: 35% • Conclusion: using language as a criterion for inclusion in a systematic review or meta-analysis may result in publication bias

  40. ODDS RATIO= 3.8 (95% CI= 1.3, 11.3) Language Bias: Egger M, et al. Lancet. 1997;350:326–329. • Randomized trials published by German investigators in either German or English journals from 1985 through 1994 • No differences in quality between German- and English-written papers • Statistically significant results: • English-written papers: 63% • German-written papers: 35% • Conclusion: using language as a criterion for inclusion in a systematic review or meta-analysis may result in publication bias

  41. ODDS RATIO= 3.8 (95% CI= 1.3, 11.3) Language Bias: Egger M, et al. Lancet. 1997;350:326–329. • Randomized trials published by German investigators in either German or English journals from 1985 through 1994 • No differences in quality between German- and English-written papers • Statistically significant results: • English-written papers: 63% • German-written papers: 35% • Conclusion: using language as a criterion for inclusion in a systematic review or meta-analysis may result in publication bias

  42. Genetic Epidemiology • Resurgence of Social Epidemiology *Relevant to Public Health

  43. Sensitivity Analysis: a Tool for Public Health Policy • Approach to examine the changes in the output (results) of a given model resulting from varying certain model parameters (or assumptions) over a reasonable range (Szklo & Nieto. Epidemiology: Beyond the Basics. 2nd Edition, Jones & Bartlett, In press).

  44. Probability of the Event (E) that Vaccines S (standard) and N (new) Are Expected to Prevent. Assume That, In Order To Determine Eligibility, Individuals in Whom Side Effects Occur Can be Identified in Advance

  45. Probability of the Event (E) that Vaccines S (standard) and N (new) Are Expected to Prevent. Assume That, In Order To Determine Eligibility, Individuals in Whom Side Effects Occur Can be Identified in Advance