Lecture 16 : The Epidemiological Transition 1 Overview

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Lecture 16 The Epidemiological Transition
(1)Overview

• CHANGES IN CAUSE OF DEATH
• POSSIBLE EXPLANATIONS
• 1. Changes In Host-Agent Relationship
• 2. Immunisation And Therapy

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Changes In Cause Of Death

• Although Sweden and France have longer records on
  the numbers of deaths, Britain has the longest
  record of the cause of death (1838).
• McKeown estimated the contribution of different
  diseases to the improvement in life expectancy
  1848-54 to 1971.
• 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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Contributions To Improvements
AIRBORNE INFECTIOUS DISEASES 40.3 Tuberculosis
17.5 Bronchitis, pneumonia, influenza
9.9 Scarlet fever, diphtheria
6.2 Measles 2.1 Smallpox
1.6 WATERBORNE / FOODBORNE INFECTIONS 21.4 Chole
ra, diarrhoea, dysentry 10.8 Typhoid
(typhus) 6.0 Non-respiratory
tuberculosis 4.6 OTHER INFECTIONS 12.6
Convulsions and teething 8.0 OTHER
CAUSES 25.6 Old age 8.7 Prematurity,
immaturity, infancy 6.2 Other 8.9
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Possible Reasons For Improvements

• Overall about 5/6 of improvement was probably due
  to decline in infections. Why did they decline?
• McKeown suggested 4 possible explanations
• Changes In Host-Agent Relationship
• Immunisation And Therapy
• Reduced Exposure To Infections
• Increased Resistance To Infections

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1. Changes In The Host-Agent Relationship

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

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2. Immunisation And Therapy

• The late 19th and 20th century saw major advances
  in the ability of the medical profession to treat
  infectious diseases.
• McKeown suggests the impact of these advances was
  less important than is generally assumed.
• Diphtheria, polio and smallpox provide examples
  of where medical interventions did make an impact.

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Airborne Diseases

• The evidence for most airborne diseases suggest
  most of the improvement occurred before effective
  medical treatment e.g.
• Tuberculosis
• Measles
• Whooping Cough
• Pneumonia
• Scarlet Fever

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Water- And Food-Borne Diseases

• Much the same conclusions apply to water- and
  food-borne diseases e.g.
• Cholera
• Diarrhoeal diseases
• Non-repiratory tuberculosis
• Typhoid

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Other Infections

• Evidence suggests similar conclusions for
• Typhus
• Tetanus
• However, medical science would appear justified
  in claiming credit for reduced deaths from
• Puerperal fever

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US Evidence

• McKinley and McKinley reported similar findings
  for the USA.
• Medical science can claim credit for at most 20
  per cent of the increase in life expectancy in
  the US in the 20th century.
• Medical science can claim virtually no credit for
  improvements in the 19th century.

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Summary

• Therapeutic medicine has played a useful role in
  the control of infectious diseases, but it did
  not really begin until the introduction of
  sulphonamides and antibiotics around 1935.
• By that time mortality from most infections had
  already fallen to a small fraction of their level
  in the mid-nineteenth century.
• McKeown claims that even after the introduction
  of chemotherapy, with the important exception of
  tuberculosis, it is probably safe to conclude
  that immunization and therapy were not the main
  influences on the further decline of the death
  rate.