Concept of disease

Dr. Rizwan S A, M.D.,Assistant Professor,

Department of Community Medicine,VMCH&RI, Madurai.

24.10.2014

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Outline

• Definition of disease– Distinction between disease, illness, sickness

• Spectrum of disease• Iceberg phenomenon• Theories of causation• Natural history of disease

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Spectrum of disease

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Iceberg phenomenon – 1/2

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Iceberg phenomenon – 2/2

1 Diseased, diagnosed & controlled

2 Diagnosed, uncontrolled

3 Undiagnosed or wronglydiagnosed disease

4 Risk factors for disease

5 Free of risk factors

Diagnosed disease

Undiagnosed orwrongly diagnosed disease

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Theories of causation

• Old theories• Modern theories– germ theory– multifactorial causation – socioeconomic, cultural,

genetic, psychological– epidemiological triad (tetrad) – web of causation– wheel of causation

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Epidemiological triad/tetrad – 1/4

Agent

EnvironmentHost

Time

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Epidemiological triad – 2/4

• Agents– Biological– Physical– Chemical – Mechanical– Insufficiency or excess of factors, hormones,

nutrients, parts, structural defects, chromosomal factors, immunological factors

– Social

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Epidemiological triad – 3/4

• Host– Demographic– Biological – genetic, biochemical, immunological,

physio functions– Social and economic– Lifestyle

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Epidemiological triad – 4/4

• Environment– Physical, – Biological, – Psychosocial

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Risk factors and risk groups

• Risk factors– Modifiable, non-modifiable– Examples for CVD

• Risk groups– Target groups– Risk approach

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Web of causation

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Wheel of causation

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Natural history of disease

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Example - TB

• Agent – types, sources, communicability• Host – age, sex, genetics, nutrition, immunity• Environment – urban slum, rural,

overcrowding, poor ventilation• Other social factors – ignorance, stigma,

health facilities, health habits, beliefs and customs

Thank You

sarizwan1986@outlook.com