The document discusses the web of causation model of disease causation. It proposes that the web of causation model better accounts for the complex interactions between multiple factors that can cause disease. The web of causation explores all predisposing factors and their interactions, rather than assuming linear relationships. It also discusses how disease prevention approaches like primordial, primary, secondary and tertiary prevention can target different points in disease development according to the web of causation model. Primary prevention methods aim to eliminate disease agents or increase resistance by actions like immunization, healthy lifestyle habits and avoiding risk factors.

1. Web of Causation of disease
&
Levels of prevention
By
Dr. Dipayan Banerjee
Dr. Ishant Kumar

2. Introduction
• Causation is an essential concept in epidemiology, yet there
is no single, clearly articulated definition for the discipline.
• From a systematic review of the literature, five categories
can be delineated: production, necessary and sufficient,
sufficient-component, counterfactual, and probabilistic.
• Strengths and weaknesses of these categories are examined
in terms of proposed characteristics of a useful scientific
definition of causation: it must be specific enough to
distinguish causation from mere correlation, but not so
narrow as to eliminate apparent causal phenomena from
consideration.

3. Contd…
• Two categories—production and counterfactual—are
present in any definition of causation but are not themselves
sufficient as definitions.
• The necessary and sufficient cause definition assumes that
all causes are deterministic.
• The sufficient-component cause definition attempts to
explain probabilistic phenomena via unknown component
causes.
• Thus, on both of these views, heavy smoking can be cited as
a cause of lung cancer only when the existence of unknown
deterministic variables is assumed.

4. • The probabilistic definition, however, avoids these
assumptions and appears to best fit the characteristics of a
useful definition of causation.
• It is also concluded that the probabilistic definition is
consistent with scientific and public health goals of
epidemiology.

5. General Models of Causation
•In epidemiology, there are several models of disease
causation that help understand disease process.
•The most widely applied models are:
- The epidemiological triad (triangle),
- The wheel, and
- The web.

6. Web of causation
• This model of disease causation was suggested by MacMahon
and Pugh and Johaness Ipsen in their book “Epidemiologic
principles and methods” in 1960
• 'Multiple causation' is the canon of contemporary epidemiology,
and its metaphor and model is the web of causation.
• the 'web' remains a widely accepted but poorly elaborated
model, reflecting in part the contemporary stress on
epidemiologic methods over epidemiologic theories of disease
causation.
• To better integrate biologic and social understandings of current
and changing population patterns of health and disease, the
essay proposes an Eco social framework for developing
epidemiologic theory.

7. • This model is ideally suited in the study of chronic disease , where the
disease agent is often not known, but is outcome of interaction of
multiple factors.
• The web of causation considers all the predisposing factors of any
kind and their complex interaction with each other.
• Natural history of disease refers to the progress of a disease process
in an individual over time, in the absence of intervention.
• The process begins with exposure to or accumulation of factors
capable of causing disease.
• Without medical intervention, the process ends with
– recovery ,
– disability,
– or death.

8. • MacMahon, Pugh, and Ipsen (1960) and Susser (1973) argued that a
linear causal chain of multiple factors does not take into account
complex precursors to each component of the chain, and these may
well overlap and may have further complex interactions.
• This web of causation explores multiple causative factors, giving each
an equal prominence in identifying determinants and relevant
interventions.
• The web of causation offers a useful way forward in understanding
aetiology and linking social determinants and social factors and
biomedical aetiological factors.

10. • The web of causation offers a useful way forward in
understanding aetiology and linking social determinants and
social factors and biomedical aetiological factors.
• Individual interventions can be employed at individual
technical levels, whereas supraindividual factors can be at
higher or second level intervening at population level health.
• Social inequalities influence the genesis and perpetuation of
certain disorders, and social determinants do affect genetic
endowments, which in turn will influence other
determinants, thus setting up a vicious or virtuous cycle,
depending upon the outcome.

12. Prevention of disease
• Preventive healthcare consists of measures taken for disease
prevention. Just as health comprises a variety of physical and
mental states, so do disease and disability, which are
affected by environmental factors, genetic predisposition,
disease agents, and lifestyle choices.
• Health, disease, and disability are dynamic processes which
begin before individuals realize they are affected. Disease
prevention relies on anticipatory actions that can be
categorized as primordial, primary, secondary, and tertiary
prevention.

13. • Each year, millions of people die of preventable deaths. A
2004 study showed that about half of all deaths in the
United States in 2000 were due to preventable behaviors
and exposures.
• Leading causes included cardiovascular disease, chronic
respiratory disease, unintentional injuries, diabetes, and
certain infectious diseases.
• There are many methods for prevention of disease. It is
recommended that adults and children aim to visit their
doctor for regular check-ups, even if they feel healthy, to
perform disease screening, identify risk factors for disease,
discuss tips for a healthy and balanced lifestyle, stay up to
date with immunizations and boosters, and maintain a good
relationship with a healthcare provider.

14. Levels of prevention
1. Primal and primordial prevention:
•Any measure aimed at helping future parents provide their upcoming
child with adequate attention, as well as secure physical and affective
environments from conception to first birthday.
•Primordial prevention refers to measures designed to avoid the
development of risk factors in the first place, early in life.
•Primal prevention has recently been propounded as a separate
category of "health promotion". This health promotion par excellence is
based on the 'new knowledge' in molecular biology, in particular on
epigenetic knowledge, which points to how much affective - as well as
physical - environment during fetal and newborn life may determine
each and every aspect of adult health

15. 2. Primary prevention:
•Methods to avoid occurrence of disease either through eliminating
disease agents or increasing resistance to disease. Examples include
immunization against disease, maintaining a healthy diet and exercise
regimen, and avoiding smoking.
•Primary prevention consists of traditional "health promotion" and
"specific protection." Health promotion activities are current, non-
clinical life choices.
•For example, eating nutritious meals and exercising daily, that both
prevent disease and create a sense of overall well-being. Preventing
disease and creating overall well-being, prolongs our life
expectancy. Health-promotional activities do not target a specific
disease or condition but rather promote health and well-being on a
very general level. On the other hand, specific protection targets a type
or group of diseases and complements the goals of health promotion.

16. 3. Secondary prevention:
•Methods to detect and address an existing disease prior to the
appearance of symptoms.
•Any screening test is an example of secondary prevention.
•Secondary prevention deals with latent diseases and attempts to
prevent an asymptomatic disease from progressing to symptomatic
disease.
•It consists of "early diagnosis and prompt treatment" to contain the
disease and prevent its spread to other individuals, and "disability
limitation" to prevent potential future complications and disabilities
from the disease.

17. 3. Tertiary prevention:
•Methods to reduce the harm of symptomatic disease, such as disability or
death, through rehabilitation and treatment. Examples include surgical
procedures that halt the spread or progression of disease.
•Tertiary prevention attempts to reduce the damage caused by symptomatic
disease by focusing on mental, physical, and social rehabilitation. Unlike
secondary prevention, which aims to prevent disability, the objective of
tertiary prevention is to maximize the remaining capabilities and functions
of an already disabled patient.
• Goals of tertiary prevention include:
-preventing pain and damage,
-halting progression and complications from disease, and
- restoring the health and functions of the individuals affected by disease.

18. Example

20. • Above figure illustrates the complexities of a causal web of
myocardial infraction.
• The basic theme of epidemiology is to study the clusters of causes
and combinations of effects and how they relate with each other.
• It can be visualized that the causal web provides a model which
shows a variety of possible intervention that could be taken which
might reduce occurance of MI.

21. Prevention in web of causation
• The web of causation does not imply that the disease can not be
controlled unless all the multiple causes or chains of causation or at
least a number of them are appropriately controlled or removed.
• Sometimes removal or elimination of just only one link or chain may
be sufficient to control disease.
• In a multifactorial event therefore individual factors are by no means
all of the equal weight. The relative importance of these factors may
be expressed in terms of “relative risk”.

22. In above example
• The prevention of myocardial infarction is based on some well
designed strategies aimed at treating both asymptomatic high risk
patient ( Primary prevention ) and patient with established CHD
(secondary prevention).
• A positive impact from primary prevention can be basically achieved
through a reduction in high blood pressure and by correcting
dyslipidemia.
• The benefit can be increased by:
-Smoking cessation
-Increase physical exercise
-Reduction of body weight
-Moderate alcohol consumption.

23. Contd..
• Secondary prevention of MI can be obtained by:
- Controlling blood pressure.
- Reducing serum cholesterol in pt. surviving acute MI who can also
benefit from administration of β-blockers , aspirin and ACE-inhibitors.

24. Intervention at different level of
prevention for MI
• Primordial prevention
1. Diet modification : diet rich in soluble fiber , vegetables, fruits and
whole grains and low in saturated fat / trans fat and cholesterol
should be encouraged.
2. Exercise
3. Low alcohol consumption
4. stop smoking

25. • Primary prevention
a.Health promotion:
- Healthy public policy
- Taxes on energy dense foods
- Tobacco and alcohol control
- Subsides for healthy food production .
b.Health education:
- Effects of alcohol and smoking
- Healthy food consumption
- Low salt intake
- Low fat intake
- Daily exercise

26. c. Specific protection:
-Blood pressure
-Lipid management
-Weight management
-Physical activity
-High level of high density lipoprotein, Vitamin D , apolipoprotein B

27. • Secondary prevention
a.Diagnosis:
- Echocardiogram
- Cardiac catheterization
- Blood tests
b. treatment:
- Aspirin
- Thrombolytic therapy
- Heparin
- Antiplatelet drugs
- ACE-inhibitors
- β- blockers

28. • Tertiary prevention
- Percutaneous coronary intervention and coronary artery bypass
grafting.
- Cardiac rehabilitation program

29. Reference:
• https://journals.sagepub.com/doi/pdf/10.1177/0020764015587629
• http://people.oregonstate.edu/~flayb/MY
%20COURSES/H671%20Advanced%20Theory
%20Winter16/Readings/Krieger%2094%20Where%20is%20the
%20spider%20of%20the%20Web%20of%20Causation.pdf
• https://www.nhp.gov.in/causation-of-diseases_mtl
• https://jech.bmj.com/content/55/12/905
• https://www.sciencedirect.com/science/article/abs/pii/02779536949
0202X
• https://www.slideshare.net/singh_br1762/concepts-of-disease-
causation-79098353
• https://en.wikipedia.org/wiki/Preventive_healthcare#Levels_of_prev
ention