Lecture 17 : The Epidemiological Transition (1) Overview

1. Lecture 17 : The Epidemiological Transition (1)Overview CHANGES IN CAUSE OF DEATH POSSIBLE EXPLANATIONS 1. Changes In Host-Agent Relationship 2. Immunisation And Therapy

2. 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.

3. 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% • Cholera, 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%

4. 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

5. 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.

6. 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.

10. 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

16. 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

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

19. 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.

22. 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.