Disease causation. lecture 2021 2022 class-1
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Dr. Muhammad Tauseef Javed discusses the rising prevalence of non-communicable diseases in developing and developed nations and presents various disease causation models, including the epidemiological triangle and the web of causation. He underscores the importance of understanding multifactorial causation and presents criteria for establishing causal relationships in epidemiology, such as strength, consistency, and biological plausibility. The document outlines how these principles can aid in the development of effective disease prevention and control measures.
![Chronic Disease Epidemiology
• Studies are undertaken to
demonstrate a link [relationship or
association] between a
condition/agent and disease
Exposure Disease
[ Condition – e.g. gene, environment ]
Dr Muhammad Tauseef Jawaid 12
5/27/2021](https://image.slidesharecdn.com/diseasecausation-210527110443/85/Disease-causation-lecture-2021-2022-class-1-12-320.jpg)
Disease causation. lecture 2021 2022 class-1
- 1. Dr Muhammad Tauseef Javed. MBBS. DPH,MSc Medical Addm. Dip-Card, M.Phil, FCPS,PhD Asct Professor Community Medicine Services Institute Of Medical Sciences Lahore. Ex-Prof Umulqurah University Makah KSA
- 2. • Q.NO.. From the past two decades Non Communicable diseases are increasing in both developing and developed countries due to which developing are experiencing double burden of diseases. • Show with diagram minimum two disease-Causation models for non Communicable disease . • Enlist the various Intervention for prevention of non Communicable disease under these causation models. Dr Muhammad Tauseef Jawaid 2 5/27/2021
- 3. The Epidemic Triangle A helpful conceptual model to frame our thoughts about infectious diseases Agent Environment Host 5/27/2021 3 Dr Muhammad Tauseef Jawaid
- 4. The Epidemiologic Triangle Agent Factors Host Factors Environmental Factors A Multi-Causal Model Agent, Host, and Environment interact This interaction is a necessary cause for infection to occur 5/27/2021 4 Dr Muhammad Tauseef Jawaid
- 5. EPIDEMIOLOGICAL / ETIOLOGICAL / ECCOLOGICAL TRIAD (contd..) • AGENT FACTORS • (PATHOGENCITY, INFECTIVITY, ) • BIOLOGICAL • NUTRIENT • CHEMICAL • PHYSICAL • MECHENICAL Dr Muhammad Tauseef Jawaid 5 5/27/2021
- 6. EPIDEMIOLOGICAL / ETIOLOGICAL / ECCOLOGICAL TRIAD (contd..) • HOST FACTORS • AGE • SEX • RACE • GENETICS • MARITAL • NUTRITION • OCCUPATION • IMMUNITY • SOCIO ECONOMIC FACTORS • LIFE STYLE Dr Muhammad Tauseef Jawaid 6 5/27/2021
- 7. EPIDEMIOLOGICAL / ETIOLOGICAL / ECCOLOGICAL TRIAD (contd..) • ENVRONMENTAL FACTORS • PHYSICAL (air, water, housing, radiation, noise etc) • BIOLOGICAL (virus, bacteria, parasites, plants, etc) • SOCIAL (religion, caste, laws, social systems, values etc) Dr Muhammad Tauseef Jawaid 7 5/27/2021
- 8. Conclusion: The Epidemiologic Triangle A model we use to frame our ideas about infection transmission Focus on it as a flexible concept Forces a big-picture approach to infectious disease epidemiology 5/27/2021 8 Dr Muhammad Tauseef Jawaid
- 9. Multifactorial causation • The concept that disease is due to multiple factors is not a new one. Pettenkofer of Munich (1819-1901) was an early proponent of this concept. But the "germ theory of disease" or "single cause idea" in the late 19th century overshadowed the multiple cause theory. Dr Muhammad Tauseef Jawaid 9 5/27/2021
- 10. Web of Causation; Exposure and Disease Outcomes
- 11. Purpose of Epidemiology • To provide a basis for developing disease control and prevention measures for groups at risk. This translates into developing measures to prevent or control disease. Dr Muhammad Tauseef Jawaid 11 5/27/2021
- 12. Chronic Disease Epidemiology • Studies are undertaken to demonstrate a link [relationship or association] between a condition/agent and disease Exposure Disease [ Condition – e.g. gene, environment ] Dr Muhammad Tauseef Jawaid 12 5/27/2021
- 13. How do we establish cause? Exposure Disease General Models of Causation Additional Factors Dr Muhammad Tauseef Jawaid 13 5/27/2021
- 14. Web of Causation • There is no single cause • Causes of disease are interacting • Illustrates the interconnectedness of possible causes RS Bhopal Dr Muhammad Tauseef Jawaid 14 5/27/2021
- 15. • Web of causation • This model of disease causation was suggested by MacMahon and Pugh in their book: "Epidemiologic Principles and Methods" (96). This model is ideally suited in the study of chronic disease, where the disease agent is often not known, but is the outcome of interaction of multiple factors. Dr Muhammad Tauseef Jawaid 15 5/27/2021
- 16. • The "web of causation" considers all the predisposing factors of any type and their complex interrelationship with each other. Fig.3 illustrates the complexities of a causal web of myocardial infarction (which is by no means complete). The basic tenet of epidemiology is to study the clusters of causes and combinations of effects and how they relate to each other ,It can be visualized that the causal web (Fig.3) provides a model which shows a variety of possible interventions that could be taken which might reduce the occurrence of myocardial infarction. Dr Muhammad Tauseef Jawaid 16 5/27/2021
- 17. Web of Causation Dr Muhammad Tauseef Jawaid 17 5/27/2021
- 18. Web of Causation - CHD Dr Muhammad Tauseef Jawaid 18 5/27/2021
- 19. Hills Criteria of Causation 5/27/2021 19 Dr Muhammad Tauseef Jawaid
- 20. Bradford Hill • Bradford Hill (1965) suggested that the following aspects of an • association be considered in attempting to distinguish causal • from non-causal associations: 5/27/2021 20 Dr Muhammad Tauseef Jawaid
- 21. Epidemiological case study • Bradford-Hill criteria Strength of association Temporality Consistency Biological plausibility Coherence Specificity Dose-response relationship Experimental evidence Analogy 5/27/2021 21 Dr Muhammad Tauseef Jawaid
- 22. 1.Temporal Relationship • Exposure always precedes the outcome. If factor "A" is believed to cause a disease, then it is clear that factor "A" must necessarily always precede the occurrence of the disease. This is the only absolutely essential criterion. 5/27/2021 22 Dr Muhammad Tauseef Jawaid
- 23. • This refers to the necessity for the exposure to precede the outcome (effect) in time • Any claim of causation must involve the cause preceding in time the presumed effect • Easier to establish in certain study designs Prospective cohort study Temporality Exposure Outcome Normal lung Cancer TIME 5/27/2021 23 Dr Muhammad Tauseef Jawaid
- 24. • This criterion negates the validity of all functional explanations used in the social sciences, including the functionalist explanations that dominated British social anthropology for so many years and the ecological functionalism that pervades much American cultural ecology. 5/27/2021 24 Dr Muhammad Tauseef Jawaid
- 25. Temporality • Temporality refers to the question of whether exposure to a risk factor precedes the disease outcome. • This criterion is important since a cause must precede an effect. Studies that fail to clarify the temporal relationship between exposure and disease therefore fail to quantify a necessary feature of a causal relationship. • Some study designs are inherently better at clarifying the issue of temporality than others. 5/27/2021 25 Dr Muhammad Tauseef Jawaid
- 26. 2. Strength: • This is defined by the size of the association as measured by appropriate statistical tests. The stronger the association, the more likely it is that the relation of "A" to "B" is causal. 5/27/2021 26 Dr Muhammad Tauseef Jawaid
- 27. • For example, the more highly correlated hypertension is with a high sodium diet, the stronger is the relation between sodium and hypertension. 5/27/2021 27 Dr Muhammad Tauseef Jawaid
- 28. Expressions of Strength of Association • Quantitatively: Effect measure (OR, RR): away from unity (the higher, the stronger the association) P-value (at 95% confidence level): less than 0.05 (the smaller, the stronger the association) • Qualitatively: Accept alternative hypothesis: an association between the studied exposure and outcome exists Reject null hypothesis: no association exists 5/27/2021 28 Dr Muhammad Tauseef Jawaid
- 29. 3.Dose-Response Relationship: • An increasing amount of exposure increases the risk. If a dose- response relationship is present, it is strong evidence for a causal relationship. 5/27/2021 29 Dr Muhammad Tauseef Jawaid
- 30. • Dose-response (‘biological gradient’) the relationship between the amount of exposure (dose) to a substance and the resulting changes in outcome (response) • If an increase in the level of exposure increases the risk of the outcome this strengthens the argument for causality Dose-response relationship < 5 cigs/day > 20 cigs/day 0 cigs/day 5 - 20 cigs/day R I S K R I S K R I S K R I S K 5/27/2021 30 Dr Muhammad Tauseef Jawaid
- 31. Percentage of people with hearing loss relative to workplace noise exposure Dose-Response Dose-response relationship Average noise level during an 8-hour working day (decibels) Exposure time (years) 5 10 40 <80 0 0 0 85 1 3 10 90 4 10 21 95 7 17 29 100 12 29 41 105 18 42 54 110 26 55 62 115 36 71 64 5/27/2021 31 Dr Muhammad Tauseef Jawaid
- 32. 4.Consistency: • The association is consistent when results are replicated in studies in different settings using different methods. 5/27/2021 32 Dr Muhammad Tauseef Jawaid
- 33. • Repeated observation of an association in studies conducted on different populations under different circumstances • If studies conducted by…. different researchers at different times in different settings on different populations using different study designs ……all produce consistent results, this strengthens the argument for causation e.g. The association between cigarette smoking and lung cancer has been consistently demonstrated in a number of different types of epidemiological study (ecological, case-control, cohort) Consistency study Epidemiological studies (1 - 14) 5/27/2021 33 Dr Muhammad Tauseef Jawaid
- 34. Consistency (II) • Meta-analysis is an good method for testing consistency. It summarizes odds ratios from various studies, excludes bias • Consistency could either mean: Exact replication (as in lab sciences, impossible in epidemiological studies) Replication under similar circumstances (possible) 5/27/2021 34 Dr Muhammad Tauseef Jawaid
- 35. 5. Plausibility: • The association agrees with currently accepted understanding of pathological processes. 5/27/2021 35 Dr Muhammad Tauseef Jawaid
- 36. Biological plausibility • This criterion links the interpretation of epidemiological information to biological data from basic science. • If an epidemiological estimate suggests an effect that is not very plausible according to other elements of current biological knowledge, it is likely that the finding represents an artifact rather than truth. 5/27/2021 36 Dr Muhammad Tauseef Jawaid
- 37. • Plausibility refers to the biological plausibility of the hypothesised causal relationship between the exposure and the outcome Is there a logical and plausible biological mechanism to explain the relationship? (Biological) Plausibility 5/27/2021 37 Dr Muhammad Tauseef Jawaid
- 38. < 200 mg caffeine/day “A high dose of caffeine could constrict a mother’s blood vessels reducing the blood flow to the placenta” (Biological Plausibility) 5/27/2021 38 Dr Muhammad Tauseef Jawaid
- 39. 6.Specificity • This is established when a single putative cause produces a specific effect. This is considered by some to be the weakest of all the criteria. • The diseases attributed to cigarette smoking, for example, do not meet this criteria. 5/27/2021 39 Dr Muhammad Tauseef Jawaid
- 40. • When specificity of an association is found, it provides additional support for a causal relationship. However, absence of specificity in no way negates a causal relationship. 5/27/2021 40 Dr Muhammad Tauseef Jawaid
- 41. 7.Coherence: • The association should be compatible with existing theory and knowledge. In other words, it is necessary to evaluate claims of causality within the context of the current state of knowledge within a given field and in related fields. 5/27/2021 41 Dr Muhammad Tauseef Jawaid
- 42. Coherence • This criterion is similar to biological plausibility, but engages a wider field of inquiry, beyond biology. • Coherence refers to the fit of an epidemiological estimate with results from any type of scientific research or theory. • As with the issue of biological plausibility, such considerations are important, but should not be viewed as necessary features of causal interpretation. 5/27/2021 42 Dr Muhammad Tauseef Jawaid
- 43. Specificity • This criterion is rarely used. However, it was included in Hill’s paper and also in the Surgeon General’s report. • In infectious diseases, it was once believed that an infectious agent would rarely be present in healthy individuals (e.g., see Koch’s or Pasteur’s postulates). 5/27/2021 43 Dr Muhammad Tauseef Jawaid
- 44. Analogy • Analogy refers to causal inference drawn from comparison or correspondence to other causal associations. Hill listed this criterion, but its usefulness is questionable and it is rarely used. 5/27/2021 44 Dr Muhammad Tauseef Jawaid
- 45. Type of Study Ability to ‘prove’ causation 1) Randomised Controlled Trial STRONG 2) Cohort Study Moderate 3) Case-control study Moderate 4) Cross-sectional study WEAK 5) Ecological study WEAK STUDY DESIGN Relative ability of different types of study to ‘prove’ causation NB: Assuming study well-designed & conducted & bias etc. minimised 5/27/2021 45 Dr Muhammad Tauseef Jawaid
- 46. Is this association causal? Does consumption of French fries by preschool children cause breast cancer? Strength Consistency Temporality Dose response Biological plausibility Study design 5/27/2021 46 Dr Muhammad Tauseef Jawaid
- 47. Is this association causal? Does consumption of French fries by preschool children cause breast cancer? Strength Weak: OR = 1.27 Consistency No Temporality Yes Dose response No Biological plausibility Yes Study design Case Control Is this association causal? 5/27/2021 47 Dr Muhammad Tauseef Jawaid
- 48. Is this association causal? Does consumption of French fries by preschool children cause breast cancer? Strength Weak: OR = 1.27 Consistency No Temporality Yes Dose response No Biological plausibility Yes Study design Case Control Is this association causal? 5/27/2021 48 Dr Muhammad Tauseef Jawaid
- 49. Is this association causal? Does cigarette smoking cause lung cancer? Strength Strong: OR, RR = 4 - 20 Consistency Yes Temporality Yes Dose response Yes Biological plausibility Yes Study design Ecological, C/S, CC, Cohort Is this association causal? 5/27/2021 49 Dr Muhammad Tauseef Jawaid
- 50. Is this association causal? Does cigarette smoking cause lung cancer? Strength Strong: OR, RR = 4 - 20 Consistency Yes Temporality Yes Dose response Yes Biological plausibility Yes Study design Ecological, C/S, CC, Cohort Is this association causal? 5/27/2021 50 Dr Muhammad Tauseef Jawaid
- 51. • Strength of the association. How large is the effect? • The consistency of the association. Has the same association been observed by others, in different populations, using a different method? • Specificity. Does altering only the cause alter the effect? • Temporal relationship. Does the cause precede the effect? Sir Bradford Hill established the following nine criteria for causation (does factor A cause disorder B). Although developed for use in the field of occupational medicine, these criteria can be used in most situations. 5/27/2021 51 Dr Muhammad Tauseef Jawaid
- 52. • Biological gradient. Is there a dose response? • Biological plausibility. Does it make sense? • Coherence. Does the evidence fit with what is known regarding the natural history and biology of the outcome? • Experimental evidence. Are there any clinical studies supporting the association? • Reasoning by analogy. Is the observed association supported by similar 5/27/2021 52 Dr Muhammad Tauseef Jawaid
- 53. Thank you for your kind attention 5/27/2021 53 Dr Muhammad Tauseef Jawaid
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