This document discusses the "web of causation" model for chronic disease epidemiology. It uses myocardial infarction (MI) as an example of a disease with multiple interacting causes. The model shows various biological and environmental factors that can increase MI risk, and how they are interrelated. It emphasizes that prevention efforts may be most effective by addressing multiple risk factors through public health strategies like health education and policies targeting diet, exercise, tobacco, and alcohol. Both population-wide primary prevention and high-risk patient secondary prevention are important to control disease in this model.

1. Web of causation
Presented by :Kumar Nyaupane

2. Introduction
• This model of disease causation was suggested
by MacMahon and Pugh in their book
“Epidemiologic principles and methods”.
• 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.

4. Contd…
• 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.

5. 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.

6. Contd…
• 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”.

7. Contd..
• Based on this theory it is believed that the
prevention offers a better prospects for health
than cure since, many of these factors can be
modified.
• Since several factors contributes to several
disease , community efforts were shifted to
factors modification ( prevention) rather than
disease treatment.

8. • 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.

9. • 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 B-blockers , aspirin and ace-
inhibitors.

10. 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

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

12. b. Specific protection
- blood [pressure
- Lipid management
- Weight management
- Physical activity
- High level of high density lipoprotein, Vitamin
D , apolipoprotein B

13. B. Secondary prevention
a. Diagnosis
- Echocardiogram
- Cardiac catheterization
- Blood tests
b. treatment
- aspirin
- thrombolytic therapy
- heparin
- Antiplatelet drugs
- ace inhibitors
- B- blockers

14. C. Tertiary prevention
- Percutaneous coronary intervention and
coronary artery bypass grafting.
- cardiac rehabilitation program