Lecture 3: History Of Disease 3 Overview

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Lecture 3 History Of Disease (3) Overview

• CHANGES IN THE CAUSE OF DEATH
• POSSIBLE REASONS FOR CHANGES
• Changes In Causal Organisms
• Medical Advances
• Reduced Exposure To Infections
• Increased Resistance To Infection
• SUMMARY
• ADDITIONAL POINTS

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Changes In Cause Of Death

• McKeown estimated the contribution of different
  diseases to the improvement in life expectancy
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• ¾ of all improvements were directly due to a
  reduction in deaths from infectious diseases.
  However, many of the remaining ¼ were also
  probably due to reductions in infectious diseases.

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McKeowns Estimates Of Contribution Of Different
Diseases To Imprements In Life Expectancy
(Abbreviated)

• Airborne Infectious Diseases 40.3
• Tuberculosis 17.5
• Bronchitis, pneumonia, influenza 9.9
• Scarlet fever, diphtheria 6.2
• Waterborne / Foodborne Infections 21.4
• Cholera, diarrhoea, dysentry 10.8
• Typhoid (typhus) 6.0
• Other Infections 12.6
• Other Causes 25.6
• Old age 8.7
• Prematurity, immaturity 6.2

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Possible Reasons For Improvements

• Changes In Causal Organisms
• Medical Advances
• Reduced Exposure To Infections
• Increased Resistance To Infection

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1. Changes in Causal Organism

• Diseases can spontanously become more or less
  virulent for no obvious reason.
• The decline in deaths from scarlet fever may be
  an example.
• Overall, such changes are probably only a minor
  factor.

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2. Medical Treatment

• The late 19th and 20th century saw major advances
  in the ability of the medical profession to treat
  infectious diseases.
• Marked reductions may be observed in the death
  rates from diphtheria and polio following medical
  interventions.
• Whilst effective, medical interventions for
  tuberculosis, measles, whooping cough and
  pneumonia arrived long after the major decline in
  the death rates.
• McKinley and McKinley reported similar findings
  for the USA.

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3. Reduced Exposure To Infections

• Lower housing densities, made possible by public
  transport and enforced by legislation, resulted
  in exposure to airborne infections.
• Improvements in water supply and sewage disposal
  resulted in reduced exposure to waterborne
  infections. Likewise pasteurisation of milk
  reduced exposure to foodborne infections.
• McKeown argues that these improvements were less
  significant than might be assumed. However, many
  experts disagree.

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4. Increased Resistance To Infection

• Having eliminated the other three possibilities,
  McKeown argues that the improvements must have
  been caused by increased resistance to infection
  due to better diets.

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Summary

• McKeowns critics argue that he underestimated
  the impact of public health reforms.
• He is also criticised for providing no direct
  evidence that improvements were due to increased
  resistance.
• Almost everyone appears to accept his arguments
  that curative medicine played a minor role.

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Additional Observations

• Public reforms with regard to housing quality,
  clean water supply and sewage disposal had the
  right effect but for the wrong reasons. The
  prevailing belief at the time was that diseases
  were caused by miasmas (bad smells).
• Life expectancies have increased in developed
  countries at a much slower rate than the growth
  of investment in curative medicine. This suggests
  that money might be more effective if spent on
  preventive measures.
• The increase in deaths from degenerative diseases
  such as cancer which mostly affect people in old
  age should be seen as positive, indicating a
  reduction in deaths at a younger age from
  infectious diseases.

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